net: fix fanout UAF in packet_release() via NETDEV_UP race
In 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.
CVE-2026-31504
Primary source · Revision 1
Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.
Security context
Source reference: cve:CVE-2026-31504
Linux
Source reference: /containers/cna/affected/0/product
- Affected versions
- Not stated in this record
- Fixed versions
- Not stated in this record
- Prerequisites
- Not stated in this record
Linux
Source reference: /containers/cna/affected/1/product
- Affected versions
- Not stated in this record
- Fixed versions
- Not stated in this record
- Prerequisites
- Not stated in this record
Structured affected-version data
Original package identities and version rules from this source.
[
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "ce06b03e60fc19c680d1bf873e779bf11c2fc518",
"lessThan": "ee642b1962caa9aa231c01abbd58bc453ae6b66e",
"versionType": "git"
},
{
"status": "affected",
"version": "ce06b03e60fc19c680d1bf873e779bf11c2fc518",
"lessThan": "42cfd7898eeed290c9fb73f732af1f7d6b0a703e",
"versionType": "git"
},
{
"status": "affected",
"version": "ce06b03e60fc19c680d1bf873e779bf11c2fc518",
"lessThan": "1b4c03f8892d955385c202009af7485364731bb9",
"versionType": "git"
},
{
"status": "affected",
"version": "ce06b03e60fc19c680d1bf873e779bf11c2fc518",
"lessThan": "654386baef228c2992dbf604c819e4c7c35fc71b",
"versionType": "git"
},
{
"status": "affected",
"version": "ce06b03e60fc19c680d1bf873e779bf11c2fc518",
"lessThan": "75fe6db23705a1d55160081f7b37db9665b1880b",
"versionType": "git"
},
{
"status": "affected",
"version": "ce06b03e60fc19c680d1bf873e779bf11c2fc518",
"lessThan": "d0c7cdc15fdf8c4f91aca1928e52295d175b6ec6",
"versionType": "git"
},
{
"status": "affected",
"version": "ce06b03e60fc19c680d1bf873e779bf11c2fc518",
"lessThan": "ceccbfc6de720ad633519a226715989cfb065af1",
"versionType": "git"
},
{
"status": "affected",
"version": "ce06b03e60fc19c680d1bf873e779bf11c2fc518",
"lessThan": "42156f93d123436f2a27c468f18c966b7e5db796",
"versionType": "git"
}
],
"programFiles": [
"net/packet/af_packet.c"
],
"defaultStatus": "unaffected"
},
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "3.1"
},
{
"status": "unaffected",
"version": "0",
"lessThan": "3.1",
"versionType": "semver"
},
{
"status": "unaffected",
"version": "5.10.253",
"versionType": "semver",
"lessThanOrEqual": "5.10.*"
},
{
"status": "unaffected",
"version": "5.15.203",
"versionType": "semver",
"lessThanOrEqual": "5.15.*"
},
{
"status": "unaffected",
"version": "6.1.168",
"versionType": "semver",
"lessThanOrEqual": "6.1.*"
},
{
"status": "unaffected",
"version": "6.6.131",
"versionType": "semver",
"lessThanOrEqual": "6.6.*"
},
{
"status": "unaffected",
"version": "6.12.80",
"versionType": "semver",
"lessThanOrEqual": "6.12.*"
},
{
"status": "unaffected",
"version": "6.18.21",
"versionType": "semver",
"lessThanOrEqual": "6.18.*"
},
{
"status": "unaffected",
"version": "6.19.11",
"versionType": "semver",
"lessThanOrEqual": "6.19.*"
},
{
"status": "unaffected",
"version": "7.0",
"versionType": "original_commit_for_fix",
"lessThanOrEqual": "*"
}
],
"programFiles": [
"net/packet/af_packet.c"
],
"defaultStatus": "affected"
}
]- Related CVEs
- CVE-2026-31504
Source reference:
/cveMetadata/cveId
Publisher severity
high
Source reference: /containers/cna/metrics
- Event
- #39910 · Revision 1
- Added to Heist Feed
- Publisher date