CVE-2026-31504
HIGH SEVERITYCVSS Score & Metrics
Base Score
7.8 / 10
Vector String
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Vulnerability Description
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.
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.
Vulnerability Details
Published Date
Last Modified
CWE ID
CWE-416
Source
NVD
Vendor
Linux
Product
Linux
External References
- https://git.kernel.org/stable/c/1b4c03f8892d955385c202009af7485364731bb9
- https://git.kernel.org/stable/c/42156f93d123436f2a27c468f18c966b7e5db796
- https://git.kernel.org/stable/c/42cfd7898eeed290c9fb73f732af1f7d6b0a703e
- https://git.kernel.org/stable/c/654386baef228c2992dbf604c819e4c7c35fc71b
- https://git.kernel.org/stable/c/75fe6db23705a1d55160081f7b37db9665b1880b
- https://git.kernel.org/stable/c/ceccbfc6de720ad633519a226715989cfb065af1
- https://git.kernel.org/stable/c/d0c7cdc15fdf8c4f91aca1928e52295d175b6ec6
- https://git.kernel.org/stable/c/ee642b1962caa9aa231c01abbd58bc453ae6b66e
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