# CVE-2026-53012: nexthop: fix IPv6 route referencing IPv4 nexthop

Status: published. Published: 2026-06-24. Updated: 2026-11-10.

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

nexthop: fix IPv6 route referencing IPv4 nexthop

syzbot reported a panic [1] [2].

When an IPv6 nexthop is replaced with an IPv4 nexthop, the has_v4 flag
of all groups containing this nexthop is not updated. This is because
nh_group_v4_update is only called when replacing AF_INET to AF_INET6,
but the reverse direction (AF_INET6 to AF_INET) is missed.

This allows a stale has_v4=false to bypass fib6_check_nexthop, causing
IPv6 routes to be attached to groups that effectively contain only AF_INET
members. Subsequent route lookups then call nexthop_fib6_nh() which
returns NULL for the AF_INET member, leading to a NULL pointer
dereference.

Fix by calling nh_group_v4_update whenever the family changes, not just
AF_INET to AF_INET6.

Reproducer:
	# AF_INET6 blackhole
	ip -6 nexthop add id 1 blackhole
	# group with has_v4=false
	ip nexthop add id 100 group 1
	# replace with AF_INET (no -6), has_v4 stays false
	ip nexthop replace id 1 blackhole
	# pass stale has_v4 check
	ip -6 route add 2001:db8::/64 nhid 100
	# panic
	ping -6 2001:db8::1

[1] https://syzkaller.appspot.com/bug?id=e17283eb2f8dcf3dd9b47fe6f67a95f71faadad0
[2] https://syzkaller.appspot.com/bug?id=8699b6ae54c9f35837d925686208402949e12ef3

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67) — https://git.kernel.org/stable/c/29c95185ba32b621fbc3800fb86e7dc3edf5c2be
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67) — https://git.kernel.org/stable/c/613c8f4a501421dd258b07ea614205d4e16ec845
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67) — https://git.kernel.org/stable/c/6275796f22bb382f3e9aa58ed0b4ef7bdad78cb8
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67) — https://git.kernel.org/stable/c/9c2d6770a5f4545a307eb66979bef7656a34d621
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67) — https://git.kernel.org/stable/c/aaac3bed034239e1d75732211d9b05f30b0b4f35
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67) — https://git.kernel.org/stable/c/ad85961004fd4bd2f31209ac4b07612c6cefb9e7
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67) — https://git.kernel.org/stable/c/b3b7e850e1541f0520c4a12ec884255c30427ff6
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67) — https://git.kernel.org/stable/c/ceffe81a0be92afc0cd1340bc8ca46559cce9bb4

## Affected products and versions

- Linux / Linux: ≥ 7bf4796dd09984ad1612877a82d0d139c70ae27f; < ceffe81a0be92afc0cd1340bc8ca46559cce9bb4 (affected, git); ≥ 7bf4796dd09984ad1612877a82d0d139c70ae27f; < 9c2d6770a5f4545a307eb66979bef7656a34d621 (affected, git); ≥ 7bf4796dd09984ad1612877a82d0d139c70ae27f; < 6275796f22bb382f3e9aa58ed0b4ef7bdad78cb8 (affected, git); ≥ 7bf4796dd09984ad1612877a82d0d139c70ae27f; < aaac3bed034239e1d75732211d9b05f30b0b4f35 (affected, git); ≥ 7bf4796dd09984ad1612877a82d0d139c70ae27f; < ad85961004fd4bd2f31209ac4b07612c6cefb9e7 (affected, git); ≥ 7bf4796dd09984ad1612877a82d0d139c70ae27f; < 613c8f4a501421dd258b07ea614205d4e16ec845 (affected, git); ≥ 7bf4796dd09984ad1612877a82d0d139c70ae27f; < b3b7e850e1541f0520c4a12ec884255c30427ff6 (affected, git); ≥ 7bf4796dd09984ad1612877a82d0d139c70ae27f; < 29c95185ba32b621fbc3800fb86e7dc3edf5c2be (affected, git). Source: CNA: Linux
- Linux / Linux: 5.3 (affected); ≥ 0; < 5.3 (unaffected, semver); ≥ 5.10.258; ≤ 5.10.* (unaffected, semver); ≥ 5.15.209; ≤ 5.15.* (unaffected, semver); ≥ 6.1.175; ≤ 6.1.* (unaffected, semver); ≥ 6.6.141; ≤ 6.6.* (unaffected, semver); ≥ 6.12.91; ≤ 6.12.* (unaffected, semver); ≥ 6.18.33; ≤ 6.18.* (unaffected, semver); ≥ 7.0.10; ≤ 7.0.* (unaffected, semver); ≥ 7.1; ≤ * (unaffected, original_commit_for_fix). Source: CNA: Linux
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0): ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0): ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0): ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0): ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0): ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP

## NVD configuration conditions

Affected CPE matches depend on the following AND/OR and negation conditions:

```json
[
  {
    "negate": false,
    "nodes": [
      {
        "cpeMatch": [
          {
            "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
            "versionEndExcluding": "5.10.258",
            "versionStartIncluding": "5.3",
            "vulnerable": true
          },
          {
            "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
            "versionEndExcluding": "5.15.209",
            "versionStartIncluding": "5.11",
            "vulnerable": true
          },
          {
            "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
            "versionEndExcluding": "6.1.175",
            "versionStartIncluding": "5.16",
            "vulnerable": true
          },
          {
            "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
            "versionEndExcluding": "6.6.141",
            "versionStartIncluding": "6.2",
            "vulnerable": true
          },
          {
            "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
            "versionEndExcluding": "6.12.91",
            "versionStartIncluding": "6.7",
            "vulnerable": true
          },
          {
            "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
            "versionEndExcluding": "6.18.33",
            "versionStartIncluding": "6.13",
            "vulnerable": true
          },
          {
            "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
            "versionEndExcluding": "7.0.10",
            "versionStartIncluding": "6.19",
            "vulnerable": true
          }
        ],
        "negate": false,
        "operator": "OR"
      }
    ],
    "operator": "OR"
  }
]
```

## Severity and prioritization

- CVSS 3.1: 5.5 (medium); CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H; source: NVD: nvd@nist.gov

- CISA KEV: No listing in collected sources

- EPSS: 0.14% as of 2026-11-09; percentile 3.12%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-476

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://git.kernel.org/stable/c/ceffe81a0be92afc0cd1340bc8ca46559cce9bb4 (CNA: Linux)

- https://git.kernel.org/stable/c/9c2d6770a5f4545a307eb66979bef7656a34d621 (CNA: Linux)

- https://git.kernel.org/stable/c/6275796f22bb382f3e9aa58ed0b4ef7bdad78cb8 (CNA: Linux)

- https://git.kernel.org/stable/c/aaac3bed034239e1d75732211d9b05f30b0b4f35 (CNA: Linux)

- https://git.kernel.org/stable/c/ad85961004fd4bd2f31209ac4b07612c6cefb9e7 (CNA: Linux)

- https://git.kernel.org/stable/c/613c8f4a501421dd258b07ea614205d4e16ec845 (CNA: Linux)

- https://git.kernel.org/stable/c/b3b7e850e1541f0520c4a12ec884255c30427ff6 (CNA: Linux)

- https://git.kernel.org/stable/c/29c95185ba32b621fbc3800fb86e7dc3edf5c2be (CNA: Linux)

- https://cert-portal.siemens.com/productcert/html/ssa-019113.html (ADP: siemens-SADP)

- https://cert-portal.siemens.com/productcert/html/ssa-457936.html (ADP: siemens-SADP)

- https://git.kernel.org/stable/c/29c95185ba32b621fbc3800fb86e7dc3edf5c2be (416baaa9-dc9f-4396-8d5f-8c081fb06d67; Patch)

- https://git.kernel.org/stable/c/613c8f4a501421dd258b07ea614205d4e16ec845 (416baaa9-dc9f-4396-8d5f-8c081fb06d67; Patch)

- https://git.kernel.org/stable/c/6275796f22bb382f3e9aa58ed0b4ef7bdad78cb8 (416baaa9-dc9f-4396-8d5f-8c081fb06d67; Patch)

- https://git.kernel.org/stable/c/9c2d6770a5f4545a307eb66979bef7656a34d621 (416baaa9-dc9f-4396-8d5f-8c081fb06d67; Patch)

- https://git.kernel.org/stable/c/aaac3bed034239e1d75732211d9b05f30b0b4f35 (416baaa9-dc9f-4396-8d5f-8c081fb06d67; Patch)

- https://git.kernel.org/stable/c/ad85961004fd4bd2f31209ac4b07612c6cefb9e7 (416baaa9-dc9f-4396-8d5f-8c081fb06d67; Patch)

- https://git.kernel.org/stable/c/b3b7e850e1541f0520c4a12ec884255c30427ff6 (416baaa9-dc9f-4396-8d5f-8c081fb06d67; Patch)

- https://git.kernel.org/stable/c/ceffe81a0be92afc0cd1340bc8ca46559cce9bb4 (416baaa9-dc9f-4396-8d5f-8c081fb06d67; Patch)

- https://cert-portal.siemens.com/productcert/html/ssa-019113.html (0b142b55-0307-4c5a-b3c9-f314f3fb7c5e)

- https://cert-portal.siemens.com/productcert/html/ssa-457936.html (0b142b55-0307-4c5a-b3c9-f314f3fb7c5e)

## Provenance

- CNA: Linux: https://www.cve.org/CVERecord?id=CVE-2026-53012; retrieved 2026-11-10; source updated 2026-11-10

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-53012; retrieved 2026-11-06; source updated 2026-11-06

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-53012; retrieved 2026-11-10; source updated Not reported

Revision: 6925cbf22133b0c0b73e2cabfb0c24b790fa4c308c0f1760d686e202b3d305f2

Canonical: https://y2.dev/cve/CVE-2026-53012

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