Linux Kernel Netfilter nft_set_pipapo Use-after-Free
CVE-2026-23351 Published on March 25, 2026
netfilter: nft_set_pipapo: split gc into unlink and reclaim phase
In the Linux kernel, the following vulnerability has been resolved:
netfilter: nft_set_pipapo: split gc into unlink and reclaim phase
Yiming Qian reports Use-after-free in the pipapo set type:
Under a large number of expired elements, commit-time GC can run for a very
long time in a non-preemptible context, triggering soft lockup warnings and
RCU stall reports (local denial of service).
We must split GC in an unlink and a reclaim phase.
We cannot queue elements for freeing until pointers have been swapped.
Expired elements are still exposed to both the packet path and userspace
dumpers via the live copy of the data structure.
call_rcu() does not protect us: dump operations or element lookups starting
after call_rcu has fired can still observe the free'd element, unless the
commit phase has made enough progress to swap the clone and live pointers
before any new reader has picked up the old version.
This a similar approach as done recently for the rbtree backend in commit
35f83a75529a ("netfilter: nft_set_rbtree: don't gc elements on insert").
Products Associated with CVE-2026-23351
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Affected Versions
Linux:- Version 3c4287f62044a90e73a561aa05fc46e62da173da and below 16f3595c0441d87dfa005c47d8f95be213afaa9e is affected.
- Version 3c4287f62044a90e73a561aa05fc46e62da173da and below 7864c667aed01a58b87ca518a631322cd0ac34c0 is affected.
- Version 3c4287f62044a90e73a561aa05fc46e62da173da and below c12d570d71920903a1a0468b7d13b085203d0c93 is affected.
- Version 3c4287f62044a90e73a561aa05fc46e62da173da and below 500a50a301ce962b019ab95053ac70264fec2c21 is affected.
- Version 3c4287f62044a90e73a561aa05fc46e62da173da and below aff13667708dfa0dce136b8efd81baa9fa6ef261 is affected.
- Version 3c4287f62044a90e73a561aa05fc46e62da173da and below 9df95785d3d8302f7c066050117b04cd3c2048c2 is affected.
- Version 5.6 is affected.
- Before 5.6 is unaffected.
- Version 6.1.167, <= 6.1.* is unaffected.
- Version 6.6.130, <= 6.6.* is unaffected.
- Version 6.12.77, <= 6.12.* is unaffected.
- Version 6.18.17, <= 6.18.* is unaffected.
- Version 6.19.7, <= 6.19.* is unaffected.
- Version 7.0-rc3, <= * is unaffected.