Vulnerability-Lookup

FKIE_CVE-2026-74656

Vulnerability from fkie_nvd - Published: 2026-08-22 16:16 - Updated: 2026-10-14 13:10

Severity

7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Summary

In the Linux kernel, the following vulnerability has been resolved: ipv4: fix use-after-free in fib_nhc_update_mtu() fib_nhc_update_mtu() walks the nexthop exception table under RTNL, but RTNL does not serialize this walk with PMTU exception updates. The walk uses rcu_dereference_protected() with a constant true condition without holding fnhe_lock. The following interleaving can therefore occur: CPU 0 CPU 1 fib_nhc_update_mtu() update_or_create_fnhe() load fnhe spin_lock_bh(&fnhe_lock) fnhe_remove_oldest() unlink fnhe kfree_rcu(fnhe, rcu) <quiescent state> access fnhe after grace period KASAN reported: BUG: KASAN: slab-use-after-free in fib_nhc_update_mtu+0x3df/0x410 Read of size 8 at addr ffff888107d49000 by task poc/90 Call Trace: fib_nhc_update_mtu+0x3df/0x410 fib_sync_mtu+0x7a/0xd0 fib_netdev_event+0x229/0x3f0 netif_set_mtu_ext+0x33a/0x570 dev_set_mtu+0x88/0x120 The same walk updates fnhe_pmtu and fnhe_mtu_locked. These fields form a pair and other writers serialize them with fnhe_lock. RCU alone prevents reclamation, but would still allow concurrent writers to leave a mixed pair. Walk the table under RCU and acquire fnhe_lock only while updating each exception. RCU keeps the current entry alive while the short critical section serializes its paired PMTU fields. This avoids holding the global lock while scanning all 2048 buckets for every nexthop.

References

	URL	Tags
	416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/5a28a4b22dde92f9d293b94236314b8d6181dc4a
	416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/63996ffc594d128ccec8fc0983f91effd2d3adc4
	416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/bc5bde9ce3cc36502839dfe98e068f7303a50982
	416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/dfe388da13aa784851e5ebbea90afbb099075761
	416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/e00f7d2b5f2540a3415a229c982af7a25ff6362e
	416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/e1e602d6b22d5cb1641c4459c487eb18bf569e0a
	416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/ed503eaad62f20cdd5122d7c3078a648a99c8f16
	416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/fd39e711866498ae94fcf9acf6f422a4f045b681

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "include/net/route.h",
            "net/ipv4/fib_semantics.c",
            "net/ipv4/route.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "fd39e711866498ae94fcf9acf6f422a4f045b681",
              "status": "affected",
              "version": "af7d6cce53694a88d6a1bb60c9a239a6a5144459",
              "versionType": "git"
            },
            {
              "lessThan": "e1e602d6b22d5cb1641c4459c487eb18bf569e0a",
              "status": "affected",
              "version": "af7d6cce53694a88d6a1bb60c9a239a6a5144459",
              "versionType": "git"
            },
            {
              "lessThan": "e00f7d2b5f2540a3415a229c982af7a25ff6362e",
              "status": "affected",
              "version": "af7d6cce53694a88d6a1bb60c9a239a6a5144459",
              "versionType": "git"
            },
            {
              "lessThan": "dfe388da13aa784851e5ebbea90afbb099075761",
              "status": "affected",
              "version": "af7d6cce53694a88d6a1bb60c9a239a6a5144459",
              "versionType": "git"
            },
            {
              "lessThan": "5a28a4b22dde92f9d293b94236314b8d6181dc4a",
              "status": "affected",
              "version": "af7d6cce53694a88d6a1bb60c9a239a6a5144459",
              "versionType": "git"
            },
            {
              "lessThan": "63996ffc594d128ccec8fc0983f91effd2d3adc4",
              "status": "affected",
              "version": "af7d6cce53694a88d6a1bb60c9a239a6a5144459",
              "versionType": "git"
            },
            {
              "lessThan": "ed503eaad62f20cdd5122d7c3078a648a99c8f16",
              "status": "affected",
              "version": "af7d6cce53694a88d6a1bb60c9a239a6a5144459",
              "versionType": "git"
            },
            {
              "lessThan": "bc5bde9ce3cc36502839dfe98e068f7303a50982",
              "status": "affected",
              "version": "af7d6cce53694a88d6a1bb60c9a239a6a5144459",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "b427832009b97a3ee412ef643a80b15372a7754d",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "2b7e4c735933be79882aba2bed9afa789e03c62f",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "8d59c3a6376bbc6dd3f7303968a719ffba75a4f1",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "9b4869cf385aa16f89c0f019eed4ec4e36aa441c",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "ff34695ced21e2dfa04d0fa1c5f6c35011fa8117",
              "versionType": "git"
            },
            {
              "lessThan": "3.17",
              "status": "affected",
              "version": "3.16.62",
              "versionType": "semver"
            },
            {
              "lessThan": "4.5",
              "status": "affected",
              "version": "4.4.162",
              "versionType": "semver"
            },
            {
              "lessThan": "4.10",
              "status": "affected",
              "version": "4.9.134",
              "versionType": "semver"
            },
            {
              "lessThan": "4.15",
              "status": "affected",
              "version": "4.14.77",
              "versionType": "semver"
            },
            {
              "lessThan": "4.19",
              "status": "affected",
              "version": "4.18.15",
              "versionType": "semver"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "include/net/route.h",
            "net/ipv4/fib_semantics.c",
            "net/ipv4/route.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "4.19"
            },
            {
              "lessThan": "4.19",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.10.*",
              "status": "unaffected",
              "version": "5.10.265",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.216",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.183",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.152",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.104",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.45",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.9",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nipv4: fix use-after-free in fib_nhc_update_mtu()\n\nfib_nhc_update_mtu() walks the nexthop exception table under RTNL, but\nRTNL does not serialize this walk with PMTU exception updates. The walk\nuses rcu_dereference_protected() with a constant true condition without\nholding fnhe_lock.\n\nThe following interleaving can therefore occur:\n\n  CPU 0                              CPU 1\n  fib_nhc_update_mtu()               update_or_create_fnhe()\n    load fnhe                          spin_lock_bh(\u0026fnhe_lock)\n                                       fnhe_remove_oldest()\n                                         unlink fnhe\n                                         kfree_rcu(fnhe, rcu)\n    \u003cquiescent state\u003e\n    access fnhe after grace period\n\nKASAN reported:\n\n  BUG: KASAN: slab-use-after-free in fib_nhc_update_mtu+0x3df/0x410\n  Read of size 8 at addr ffff888107d49000 by task poc/90\n  Call Trace:\n   fib_nhc_update_mtu+0x3df/0x410\n   fib_sync_mtu+0x7a/0xd0\n   fib_netdev_event+0x229/0x3f0\n   netif_set_mtu_ext+0x33a/0x570\n   dev_set_mtu+0x88/0x120\n\nThe same walk updates fnhe_pmtu and fnhe_mtu_locked. These fields form a\npair and other writers serialize them with fnhe_lock. RCU alone prevents\nreclamation, but would still allow concurrent writers to leave a mixed\npair.\n\nWalk the table under RCU and acquire fnhe_lock only while updating each\nexception. RCU keeps the current entry alive while the short critical\nsection serializes its paired PMTU fields. This avoids holding the global\nlock while scanning all 2048 buckets for every nexthop."
    },
    {
      "lang": "es",
      "value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\nipv4: correcci\u00f3n de uso despu\u00e9s de liberaci\u00f3n en fib_nhc_update_mtu()\n\nfib_nhc_update_mtu() recorre la tabla de excepciones del siguiente salto bajo RTNL, pero RTNL no serializa este recorrido con las actualizaciones de excepciones PMTU. El recorrido utiliza rcu_dereference_protected() con una condici\u00f3n verdadera constante sin mantener fnhe_lock.\n\nEl siguiente entrelazado puede, por lo tanto, ocurrir:\n\n  CPU 0                              CPU 1\n  fib_nhc_update_mtu()               update_or_create_fnhe()\n    load fnhe                          spin_lock_bh(\u0026fnhe_lock)\n                                       fnhe_remove_oldest()\n                                         unlink fnhe\n                                         kfree_rcu(fnhe, rcu)\n    \u003cquiescent state\u003e\n    access fnhe after grace period\n\nKASAN inform\u00f3:\n\n  BUG: KASAN: slab-uso despu\u00e9s de liberaci\u00f3n en fib_nhc_update_mtu+0x3df/0x410\n  Read of size 8 at addr ffff888107d49000 by task PoC/90\n  Call Trace:\n   fib_nhc_update_mtu+0x3df/0x410\n   fib_sync_mtu+0x7a/0xd0\n   fib_netdev_event+0x229/0x3f0\n   netif_set_mtu_ext+0x33a/0x570\n   dev_set_mtu+0x88/0x120\n\nEl mismo recorrido actualiza fnhe_pmtu y fnhe_mtu_locked. Estos campos forman un par y otros escritores los serializan con fnhe_lock. RCU por s\u00ed solo previene la recuperaci\u00f3n, pero a\u00fan permitir\u00eda a escritores concurrentes dejar un par mixto.\n\nRecorrer la tabla bajo RCU y adquirir fnhe_lock solo mientras se actualiza cada excepci\u00f3n. RCU mantiene la entrada actual viva mientras la secci\u00f3n cr\u00edtica corta serializa sus campos PMTU emparejados. Esto evita mantener el bloqueo global mientras se escanean todos los 2048 cubos para cada siguiente salto."
    }
  ],
  "id": "CVE-2026-74656",
  "lastModified": "2026-10-14T13:10:00.187",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "LOCAL",
          "availabilityImpact": "HIGH",
          "baseScore": 7.8,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 1.8,
        "impactScore": 5.9,
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-08-22T16:16:39.177",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/5a28a4b22dde92f9d293b94236314b8d6181dc4a"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/63996ffc594d128ccec8fc0983f91effd2d3adc4"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/bc5bde9ce3cc36502839dfe98e068f7303a50982"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/dfe388da13aa784851e5ebbea90afbb099075761"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/e00f7d2b5f2540a3415a229c982af7a25ff6362e"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/e1e602d6b22d5cb1641c4459c487eb18bf569e0a"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/ed503eaad62f20cdd5122d7c3078a648a99c8f16"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/fd39e711866498ae94fcf9acf6f422a4f045b681"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}

CVE-2026-74656 (GCVE-0-2026-74656)

Vulnerability from cvelistv5 – Published: 2026-08-22 15:32 – Updated: 2026-08-25 05:41

Title

ipv4: fix use-after-free in fib_nhc_update_mtu()

Summary

Severity

7.8 (High)


                        
                          CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Assigner

Linux CNA under the mitre root

CNA scorecard D 53/100 over 6667 records in the last 180 days details

References

8 references

URL	Tags
https://git.kernel.org/stable/c/fd39e711866498ae9…
https://git.kernel.org/stable/c/e1e602d6b22d5cb16…
https://git.kernel.org/stable/c/e00f7d2b5f2540a34…
https://git.kernel.org/stable/c/dfe388da13aa78485…
https://git.kernel.org/stable/c/5a28a4b22dde92f9d…
https://git.kernel.org/stable/c/63996ffc594d128cc…
https://git.kernel.org/stable/c/ed503eaad62f20cdd…
https://git.kernel.org/stable/c/bc5bde9ce3cc36502…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: af7d6cce53694a88d6a1bb60c9a239a6a5144459 , < fd39e711866498ae94fcf9acf6f422a4f045b681 (git) Affected: af7d6cce53694a88d6a1bb60c9a239a6a5144459 , < e1e602d6b22d5cb1641c4459c487eb18bf569e0a (git) Affected: af7d6cce53694a88d6a1bb60c9a239a6a5144459 , < e00f7d2b5f2540a3415a229c982af7a25ff6362e (git) Affected: af7d6cce53694a88d6a1bb60c9a239a6a5144459 , < dfe388da13aa784851e5ebbea90afbb099075761 (git) Affected: af7d6cce53694a88d6a1bb60c9a239a6a5144459 , < 5a28a4b22dde92f9d293b94236314b8d6181dc4a (git) Affected: af7d6cce53694a88d6a1bb60c9a239a6a5144459 , < 63996ffc594d128ccec8fc0983f91effd2d3adc4 (git) Affected: af7d6cce53694a88d6a1bb60c9a239a6a5144459 , < ed503eaad62f20cdd5122d7c3078a648a99c8f16 (git) Affected: af7d6cce53694a88d6a1bb60c9a239a6a5144459 , < bc5bde9ce3cc36502839dfe98e068f7303a50982 (git) Affected: b427832009b97a3ee412ef643a80b15372a7754d (git) Affected: 2b7e4c735933be79882aba2bed9afa789e03c62f (git) Affected: 8d59c3a6376bbc6dd3f7303968a719ffba75a4f1 (git) Affected: 9b4869cf385aa16f89c0f019eed4ec4e36aa441c (git) Affected: ff34695ced21e2dfa04d0fa1c5f6c35011fa8117 (git) Affected: 3.16.62 , < 3.17 (semver) Affected: 4.4.162 , < 4.5 (semver) Affected: 4.9.134 , < 4.10 (semver) Affected: 4.14.77 , < 4.15 (semver) Affected: 4.18.15 , < 4.19 (semver)
Linux	Linux	Affected: 4.19 Unaffected: 0 , < 4.19 (semver) Unaffected: 5.10.265 , ≤ 5.10.* (semver) Unaffected: 5.15.216 , ≤ 5.15.* (semver) Unaffected: 6.1.183 , ≤ 6.1.* (semver) Unaffected: 6.6.152 , ≤ 6.6.* (semver) Unaffected: 6.12.104 , ≤ 6.12.* (semver) Unaffected: 6.18.45 , ≤ 6.18.* (semver) Unaffected: 7.1.9 , ≤ 7.1.* (semver) Unaffected: 7.2 , ≤ * (original_commit_for_fix)

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "include/net/route.h",
            "net/ipv4/fib_semantics.c",
            "net/ipv4/route.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "fd39e711866498ae94fcf9acf6f422a4f045b681",
              "status": "affected",
              "version": "af7d6cce53694a88d6a1bb60c9a239a6a5144459",
              "versionType": "git"
            },
            {
              "lessThan": "e1e602d6b22d5cb1641c4459c487eb18bf569e0a",
              "status": "affected",
              "version": "af7d6cce53694a88d6a1bb60c9a239a6a5144459",
              "versionType": "git"
            },
            {
              "lessThan": "e00f7d2b5f2540a3415a229c982af7a25ff6362e",
              "status": "affected",
              "version": "af7d6cce53694a88d6a1bb60c9a239a6a5144459",
              "versionType": "git"
            },
            {
              "lessThan": "dfe388da13aa784851e5ebbea90afbb099075761",
              "status": "affected",
              "version": "af7d6cce53694a88d6a1bb60c9a239a6a5144459",
              "versionType": "git"
            },
            {
              "lessThan": "5a28a4b22dde92f9d293b94236314b8d6181dc4a",
              "status": "affected",
              "version": "af7d6cce53694a88d6a1bb60c9a239a6a5144459",
              "versionType": "git"
            },
            {
              "lessThan": "63996ffc594d128ccec8fc0983f91effd2d3adc4",
              "status": "affected",
              "version": "af7d6cce53694a88d6a1bb60c9a239a6a5144459",
              "versionType": "git"
            },
            {
              "lessThan": "ed503eaad62f20cdd5122d7c3078a648a99c8f16",
              "status": "affected",
              "version": "af7d6cce53694a88d6a1bb60c9a239a6a5144459",
              "versionType": "git"
            },
            {
              "lessThan": "bc5bde9ce3cc36502839dfe98e068f7303a50982",
              "status": "affected",
              "version": "af7d6cce53694a88d6a1bb60c9a239a6a5144459",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "b427832009b97a3ee412ef643a80b15372a7754d",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "2b7e4c735933be79882aba2bed9afa789e03c62f",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "8d59c3a6376bbc6dd3f7303968a719ffba75a4f1",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "9b4869cf385aa16f89c0f019eed4ec4e36aa441c",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "ff34695ced21e2dfa04d0fa1c5f6c35011fa8117",
              "versionType": "git"
            },
            {
              "lessThan": "3.17",
              "status": "affected",
              "version": "3.16.62",
              "versionType": "semver"
            },
            {
              "lessThan": "4.5",
              "status": "affected",
              "version": "4.4.162",
              "versionType": "semver"
            },
            {
              "lessThan": "4.10",
              "status": "affected",
              "version": "4.9.134",
              "versionType": "semver"
            },
            {
              "lessThan": "4.15",
              "status": "affected",
              "version": "4.14.77",
              "versionType": "semver"
            },
            {
              "lessThan": "4.19",
              "status": "affected",
              "version": "4.18.15",
              "versionType": "semver"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "include/net/route.h",
            "net/ipv4/fib_semantics.c",
            "net/ipv4/route.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "4.19"
            },
            {
              "lessThan": "4.19",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.10.*",
              "status": "unaffected",
              "version": "5.10.265",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.216",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.183",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.152",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.104",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.45",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.9",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.10.265",
                  "versionStartIncluding": "4.19",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.15.216",
                  "versionStartIncluding": "4.19",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.1.183",
                  "versionStartIncluding": "4.19",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.6.152",
                  "versionStartIncluding": "4.19",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.12.104",
                  "versionStartIncluding": "4.19",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.45",
                  "versionStartIncluding": "4.19",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.1.9",
                  "versionStartIncluding": "4.19",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2",
                  "versionStartIncluding": "4.19",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionStartIncluding": "3.16.62",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionStartIncluding": "4.4.162",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionStartIncluding": "4.9.134",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionStartIncluding": "4.14.77",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionStartIncluding": "4.18.15",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nipv4: fix use-after-free in fib_nhc_update_mtu()\n\nfib_nhc_update_mtu() walks the nexthop exception table under RTNL, but\nRTNL does not serialize this walk with PMTU exception updates. The walk\nuses rcu_dereference_protected() with a constant true condition without\nholding fnhe_lock.\n\nThe following interleaving can therefore occur:\n\n  CPU 0                              CPU 1\n  fib_nhc_update_mtu()               update_or_create_fnhe()\n    load fnhe                          spin_lock_bh(\u0026fnhe_lock)\n                                       fnhe_remove_oldest()\n                                         unlink fnhe\n                                         kfree_rcu(fnhe, rcu)\n    \u003cquiescent state\u003e\n    access fnhe after grace period\n\nKASAN reported:\n\n  BUG: KASAN: slab-use-after-free in fib_nhc_update_mtu+0x3df/0x410\n  Read of size 8 at addr ffff888107d49000 by task poc/90\n  Call Trace:\n   fib_nhc_update_mtu+0x3df/0x410\n   fib_sync_mtu+0x7a/0xd0\n   fib_netdev_event+0x229/0x3f0\n   netif_set_mtu_ext+0x33a/0x570\n   dev_set_mtu+0x88/0x120\n\nThe same walk updates fnhe_pmtu and fnhe_mtu_locked. These fields form a\npair and other writers serialize them with fnhe_lock. RCU alone prevents\nreclamation, but would still allow concurrent writers to leave a mixed\npair.\n\nWalk the table under RCU and acquire fnhe_lock only while updating each\nexception. RCU keeps the current entry alive while the short critical\nsection serializes its paired PMTU fields. This avoids holding the global\nlock while scanning all 2048 buckets for every nexthop."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The UAF is hit in fib_nhc_update_mtu(), entered only via NETDEV_CHANGEMTU from dev_set_mtu()/netif_set_mtu_ext() (SIOCSIFMTU or RTM_NEWLINK IFLA_MTU); per kernel CNA guidance this administrative netdev path is Local even though the racing update_or_create_fnhe() leg is driven by received ICMP PMTU packets.\nAC:L - KASAN reproduced this from task poc/90 by racing dev_set_mtu() against concurrent PMTU exception creation/eviction; an attacker controls both CPUs by running an MTU-change thread alongside ICMP or socket traffic that floods update_or_create_fnhe() and fnhe_remove_oldest(), without depending on uncontrollable victim state.\nPR:L - Changing interface MTU requires CAP_NET_ADMIN checked via ns_capable(net-\u003euser_ns, CAP_NET_ADMIN) on SIOCSIFMTU and RTM_SETLINK; unprivileged local users obtain this in a user+network namespace (unshare -Urn) and can then race MTU changes against PMTU exception updates on the same host.\nUI:N - Exploitation requires only the attacker\u0027s own MTU ioctl/netlink operations and concurrent network or socket traffic to populate/evict fib_nh_exception entries; no victim mount, click, or other voluntary action is needed beyond normal host networking.\nS:U - The slab use-after-free corrupts host kernel IPv4 routing state within the same kernel security authority; it is not a VM escape, IOMMU bypass, or other cross-boundary scope change.\nC:H - KASAN reported a slab use-after-free read of 8 bytes in fib_nhc_update_mtu() on a fib_nh_exception freed by kfree_rcu() from fnhe_remove_oldest(); UAF on this kmalloc object enables heap grooming for arbitrary kernel memory disclosure.\nI:H - The buggy walk both reads and writes fnhe_pmtu and fnhe_mtu_locked on potentially freed fib_nh_exception objects without fnhe_lock, providing standard slab reuse primitives for attacker-controlled kernel writes and potential control-flow hijack.\nA:H - The confirmed KASAN slab-use-after-free in fib_nhc_update_mtu() can immediately BUG/oops the kernel; the attacker can retrigger the race by repeating MTU toggles concurrent with PMTU exception flooding for persistent denial of service."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-25T05:41:13.058Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/fd39e711866498ae94fcf9acf6f422a4f045b681"
        },
        {
          "url": "https://git.kernel.org/stable/c/e1e602d6b22d5cb1641c4459c487eb18bf569e0a"
        },
        {
          "url": "https://git.kernel.org/stable/c/e00f7d2b5f2540a3415a229c982af7a25ff6362e"
        },
        {
          "url": "https://git.kernel.org/stable/c/dfe388da13aa784851e5ebbea90afbb099075761"
        },
        {
          "url": "https://git.kernel.org/stable/c/5a28a4b22dde92f9d293b94236314b8d6181dc4a"
        },
        {
          "url": "https://git.kernel.org/stable/c/63996ffc594d128ccec8fc0983f91effd2d3adc4"
        },
        {
          "url": "https://git.kernel.org/stable/c/ed503eaad62f20cdd5122d7c3078a648a99c8f16"
        },
        {
          "url": "https://git.kernel.org/stable/c/bc5bde9ce3cc36502839dfe98e068f7303a50982"
        }
      ],
      "title": "ipv4: fix use-after-free in fib_nhc_update_mtu()",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-74656",
    "datePublished": "2026-08-22T15:32:30.729Z",
    "dateReserved": "2026-08-15T05:44:03.923Z",
    "dateUpdated": "2026-08-25T05:41:13.058Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Vulnerability timeline

Sightings and recorded dates, grouped by day · UTC

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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

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