CVE-2026-23270

Summary

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

net/sched: Only allow act_ct to bind to clsact/ingress qdiscs and shared blocks

As Paolo said earlier [1]:

"Since the blamed commit below, classify can return TC_ACT_CONSUMED while the current skb being held by the defragmentation engine. As reported by GangMin Kim, if such packet is that may cause a UaF when the defrag engine later on tries to tuch again such packet."

act_ct was never meant to be used in the egress path, however some users are attaching it to egress today [2]. Attempting to reach a middle ground, we noticed that, while most qdiscs are not handling TC_ACT_CONSUMED, clsact/ingress qdiscs are. With that in mind, we address the issue by only allowing act_ct to bind to clsact/ingress qdiscs and shared blocks. That way it's still possible to attach act_ct to egress (albeit only with clsact).

[1] https://lore.kernel.org/netdev/674b8cbfc385c6f37fb29a1de08d8fe5c2b0fbee.1771321118.git.pabeni@redhat.com/ [2] https://lore.kernel.org/netdev/cc6bfb4a-4a2b-42d8-b9ce-7ef6644fb22b@ovn.org/

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/bc4e5bb529823a09f02dbe96169de679a9db26e0
• https://git.kernel.org/stable/c/fb3c380a54e33d1fd272cc342faa906d787d7ef1
• https://git.kernel.org/stable/c/5a110ddcc99bda77a28598b3555fe009eaab3828
• https://git.kernel.org/stable/c/524ce8b4ea8f64900b6c52b6a28df74f6bc0801e
• https://git.kernel.org/stable/c/380ad8b7c65ea7aa10ef2258297079ed5ac1f5b6
• https://git.kernel.org/stable/c/9deda0fcda5c1f388c5e279541850b71a2ccfcf4
• https://git.kernel.org/stable/c/11cb63b0d1a0685e0831ae3c77223e002ef18189

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