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CVE-2026-31504 In the Linux kernel, the following vulnerability has been resolved: net: fix fanout UAF in packet_release() via…

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.

Affected products and versions

Product Affected versions Fixed in
Linux 7.0 earliest → < 7.0 7.0
Linux 6.19 earliest → < 6.19.11 6.19.11
Linux 6.18 earliest → < 6.18.21 6.18.21
Linux 6.12 earliest → < 6.12.80 6.12.80
Linux 6.6 earliest → < 6.6.131 6.6.131
Linux 6.1 earliest → < 6.1.168 6.1.168
Linux 5.15 earliest → < 5.15.203 5.15.203
Linux 5.10 earliest → < 5.10.253 5.10.253
Linux 3.1 No fix stated
Show the 3 other branches
Product Affected versions Fixed in
SIMATIC S7-1500 CPU 1518-4 PN/DP MFP 3.1 3.1.7 → latest No fix stated
SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP 3.1 3.1.7 → latest No fix stated
SIPLUS S7-1500 CPU 1518-4 PN/DP MFP 3.1 3.1.7 → latest No fix stated

References

Timeline

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