net: fix fanout UAF in packet_release() via NETDEV_UP race

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Summary

CVECVE-2026-31504
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-22 14:16:49 UTC
Updated2026-04-28 15:07:06 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: net: fix fanout UAF in packet_release() via NETDEV_UP race `packet_release()` has a race window where `NETDEV_UP` can re-register a socket into a fanout group's `arr[]` array. The re-registration is not cleaned up by `fanout_release()`, leaving a dangling pointer in the fanout array. `packet_release()` does NOT zero `po->num` in its `bind_lock` section. After releasing `bind_lock`, `po->num` is still non-zero and `po->ifindex` still matches the bound device. A concurrent `packet_notifier(NETDEV_UP)` that already found the socket in `sklist` can re-register the hook. For fanout sockets, this re-registration calls `__fanout_link(sk, po)` which adds the socket back into `f->arr[]` and increments `f->num_members`, but does NOT increment `f->sk_ref`. The fix sets `po->num` to zero in `packet_release` while `bind_lock` is held to prevent NETDEV_UP from linking, preventing the race window. This bug was found following an additional audit with Claude Code based on CVE-2025-38617.

Risk And Classification

Primary CVSS: v3.1 7.8 HIGH from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

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

EPSS: 0.000240000 probability, percentile 0.067850000 (date 2026-04-27)

Problem Types: CWE-416

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
3.1CNADECLARED7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected ce06b03e60fc19c680d1bf873e779bf11c2fc518 ee642b1962caa9aa231c01abbd58bc453ae6b66e git Not specified
CNA Linux Linux affected ce06b03e60fc19c680d1bf873e779bf11c2fc518 42cfd7898eeed290c9fb73f732af1f7d6b0a703e git Not specified
CNA Linux Linux affected ce06b03e60fc19c680d1bf873e779bf11c2fc518 1b4c03f8892d955385c202009af7485364731bb9 git Not specified
CNA Linux Linux affected ce06b03e60fc19c680d1bf873e779bf11c2fc518 654386baef228c2992dbf604c819e4c7c35fc71b git Not specified
CNA Linux Linux affected ce06b03e60fc19c680d1bf873e779bf11c2fc518 75fe6db23705a1d55160081f7b37db9665b1880b git Not specified
CNA Linux Linux affected ce06b03e60fc19c680d1bf873e779bf11c2fc518 d0c7cdc15fdf8c4f91aca1928e52295d175b6ec6 git Not specified
CNA Linux Linux affected ce06b03e60fc19c680d1bf873e779bf11c2fc518 ceccbfc6de720ad633519a226715989cfb065af1 git Not specified
CNA Linux Linux affected ce06b03e60fc19c680d1bf873e779bf11c2fc518 42156f93d123436f2a27c468f18c966b7e5db796 git Not specified
CNA Linux Linux affected 3.1 Not specified
CNA Linux Linux unaffected 3.1 semver Not specified
CNA Linux Linux unaffected 5.10.253 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.203 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.168 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.131 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.80 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.21 6.18.* semver Not specified
CNA Linux Linux unaffected 6.19.11 6.19.* semver Not specified
CNA Linux Linux unaffected 7.0 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/42cfd7898eeed290c9fb73f732af1f7d6b0a703e 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/ee642b1962caa9aa231c01abbd58bc453ae6b66e 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/1b4c03f8892d955385c202009af7485364731bb9 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/75fe6db23705a1d55160081f7b37db9665b1880b 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/ceccbfc6de720ad633519a226715989cfb065af1 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/d0c7cdc15fdf8c4f91aca1928e52295d175b6ec6 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/654386baef228c2992dbf604c819e4c7c35fc71b 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/42156f93d123436f2a27c468f18c966b7e5db796 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
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