FKIE_CVE-2026-74656
Vulnerability from fkie_nvd - Published: 2026-08-22 16:16 - Updated: 2026-08-25 06:18
Severity
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
Impacted products
| Vendor | Product | Version |
|---|
{
"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."
}
],
"id": "CVE-2026-74656",
"lastModified": "2026-08-25T06:18:46.560",
"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"
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
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.
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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.
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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