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GHSA-JM3Q-XWGV-HGH8

Vulnerability from github – Published: 2026-08-28 09:31 – Updated: 2026-08-29 09:30

Details

In the Linux kernel, the following vulnerability has been resolved:

netfilter: flowtable: avoid num_encaps underflow on bridge VLAN untag

The DEV_PATH_BR_VLAN_UNTAG case post-decrements info->num_encaps inside WARN_ON_ONCE(). num_encaps is u8, so if it's already 0 the decrement still happens and wraps it to 255. The break only leaves the inner switch -- a later path entry can set info->indev back to a real device, and we end up returning with num_encaps == 255.

nft_dev_forward_path() then walks info.encap[] (size 2) up to num_encaps, which means an OOB stack read and a bogus count copied into the route descriptor.

Should only happen on a malformed bridge path stack, hence the WARN, but worth handling sanely. Move the decrement out of the WARN.

[ While at this, remove the WARN_ON_ONCE since this can only happen with a buggy bridge path stack --pablo ].

Severity

9.8 (Critical)


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

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{
  "affected": [],
  "aliases": [
    "CVE-2026-80634"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-08-28T08:16:48Z",
    "severity": "CRITICAL"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: flowtable: avoid num_encaps underflow on bridge VLAN untag\n\nThe DEV_PATH_BR_VLAN_UNTAG case post-decrements info-\u003enum_encaps\ninside WARN_ON_ONCE(). num_encaps is u8, so if it\u0027s already 0 the\ndecrement still happens and wraps it to 255. The break only leaves\nthe inner switch -- a later path entry can set info-\u003eindev back to\na real device, and we end up returning with num_encaps == 255.\n\nnft_dev_forward_path() then walks info.encap[] (size 2) up to\nnum_encaps, which means an OOB stack read and a bogus count copied\ninto the route descriptor.\n\nShould only happen on a malformed bridge path stack, hence the WARN,\nbut worth handling sanely. Move the decrement out of the WARN.\n\n[ While at this, remove the WARN_ON_ONCE since this can only happen\n  with a buggy bridge path stack --pablo ].",
  "id": "GHSA-jm3q-xwgv-hgh8",
  "modified": "2026-08-29T09:30:26Z",
  "published": "2026-08-28T09:31:47Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-80634"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/2f55fa28011c97d6495d5787808db10a8c2d690d"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/e052f920773b73be49eb4d8702a9f85de7464363"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}

CVE-2026-80634 (GCVE-0-2026-80634)

Vulnerability from cvelistv5 – Published: 2026-08-28 06:48 – Updated: 2026-08-29 06:21

Title

netfilter: flowtable: avoid num_encaps underflow on bridge VLAN untag

Summary

In the Linux kernel, the following vulnerability has been resolved: netfilter: flowtable: avoid num_encaps underflow on bridge VLAN untag The DEV_PATH_BR_VLAN_UNTAG case post-decrements info->num_encaps inside WARN_ON_ONCE(). num_encaps is u8, so if it's already 0 the decrement still happens and wraps it to 255. The break only leaves the inner switch -- a later path entry can set info->indev back to a real device, and we end up returning with num_encaps == 255. nft_dev_forward_path() then walks info.encap[] (size 2) up to num_encaps, which means an OOB stack read and a bogus count copied into the route descriptor. Should only happen on a malformed bridge path stack, hence the WARN, but worth handling sanely. Move the decrement out of the WARN. [ While at this, remove the WARN_ON_ONCE since this can only happen with a buggy bridge path stack --pablo ].

Severity

9.8 (Critical)


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

Assigner

Linux mitre root

References

2 references

URL	Tags
https://git.kernel.org/stable/c/2f55fa28011c97d64…
https://git.kernel.org/stable/c/e052f920773b73be4…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: e990cef6516daa4e1e236433579e333f74fd38cb , < 2f55fa28011c97d6495d5787808db10a8c2d690d (git) Affected: e990cef6516daa4e1e236433579e333f74fd38cb , < e052f920773b73be49eb4d8702a9f85de7464363 (git)
Linux	Linux	Affected: 5.13 Unaffected: 0 , < 5.13 (semver) Unaffected: 7.1.5 , ≤ 7.1.* (semver) Unaffected: 7.2 , ≤ * (original_commit_for_fix)

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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/netfilter/nf_flow_table_path.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "2f55fa28011c97d6495d5787808db10a8c2d690d",
              "status": "affected",
              "version": "e990cef6516daa4e1e236433579e333f74fd38cb",
              "versionType": "git"
            },
            {
              "lessThan": "e052f920773b73be49eb4d8702a9f85de7464363",
              "status": "affected",
              "version": "e990cef6516daa4e1e236433579e333f74fd38cb",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "net/netfilter/nf_flow_table_path.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "5.13"
            },
            {
              "lessThan": "5.13",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.5",
              "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": "7.1.5",
                  "versionStartIncluding": "5.13",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2",
                  "versionStartIncluding": "5.13",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: flowtable: avoid num_encaps underflow on bridge VLAN untag\n\nThe DEV_PATH_BR_VLAN_UNTAG case post-decrements info-\u003enum_encaps\ninside WARN_ON_ONCE(). num_encaps is u8, so if it\u0027s already 0 the\ndecrement still happens and wraps it to 255. The break only leaves\nthe inner switch -- a later path entry can set info-\u003eindev back to\na real device, and we end up returning with num_encaps == 255.\n\nnft_dev_forward_path() then walks info.encap[] (size 2) up to\nnum_encaps, which means an OOB stack read and a bogus count copied\ninto the route descriptor.\n\nShould only happen on a malformed bridge path stack, hence the WARN,\nbut worth handling sanely. Move the decrement out of the WARN.\n\n[ While at this, remove the WARN_ON_ONCE since this can only happen\n  with a buggy bridge path stack --pablo ]."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 9.8,
            "baseSeverity": "CRITICAL",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - The bug is hit in nft_flow_offload_eval on NF_INET_FORWARD when remotely sourced TCP/UDP packets matching a conntrack flow trigger nft_flow_route() and nft_dev_forward_path() during softirq packet processing on nftables flowtable routers/gateways, not via netlink configuration APIs.\nAC:L - Once an nftables flowtable with bridge VLAN filtering is deployed, an attacker can establish confirmed TCP/UDP flows and steer traffic through the affected bridge/VLAN topology to reach nft_dev_path_info() without races or other conditions outside the attacker\u0027s control.\nPR:N - Flowtable and bridge VLAN setup are administrator deployment prerequisites; a remote sender needs no local account, authentication, or CAP_NET_ADMIN on the victim to trigger flow offload path resolution while forwarding traffic through the configured bridge.\nUI:N - Exploitation requires only sending network packets processed automatically on the forwarding path; no victim must open files, mount filesystems, or take any interactive action beyond normal traffic through the router.\nS:U - Out-of-bounds stack reads and writes in nft_dev_forward_path() corrupt kernel stack memory and route descriptors on the affected host only; this is standard kernel compromise within one security authority, not a VM escape or cross-boundary sandbox break.\nC:H - When num_encaps underflows to 255, nft_dev_forward_path() loops up to 255 times over info.encap[2], performing out-of-bounds stack reads of adjacent kernel stack memory that can disclose pointers and other sensitive data.\nI:H - The same loop writes attacker-influenced encap values past route-\u003etuple[].in.encap[2] on the stack, corrupting adjacent route fields and stack data in ways that can be leveraged for arbitrary kernel writes and control-flow hijack.\nA:H - Massive out-of-bounds stack corruption during flow offload setup in softirq context can cause immediate kernel oops/panic and reliable denial of service on forwarding routers processing malicious traffic through vulnerable bridge VLAN paths."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-29T06:21:33.944Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/2f55fa28011c97d6495d5787808db10a8c2d690d"
        },
        {
          "url": "https://git.kernel.org/stable/c/e052f920773b73be49eb4d8702a9f85de7464363"
        }
      ],
      "title": "netfilter: flowtable: avoid num_encaps underflow on bridge VLAN untag",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-80634",
    "datePublished": "2026-08-28T06:48:49.022Z",
    "dateReserved": "2026-08-26T14:34:25.777Z",
    "dateUpdated": "2026-08-29T06:21:33.944Z",
    "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.

Detection rules are retrieved from Rulezet.

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.

Action not permitted

GHSA-JM3Q-XWGV-HGH8

CVE-2026-80634 (GCVE-0-2026-80634)

Tags

Sightings

Nomenclature