CVE-2026-23111 — netfilter: nf_tables: fix inverted genmask check in nft_map_catchall_activate()

Description (CNA)

In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_tables: fix inverted genmask check in nft_map_catchall_activate() nft_map_catchall_activate() has an inverted element activity check compared to its non-catchall counterpart nft_mapelem_activate() and compared to what is logically required. nft_map_catchall_activate() is called from the abort path to re-activate catchall map elements that were deactivated during a failed transaction. It should skip elements that are already active (they don't need re-activation) and process elements that are inactive (they need to be restored). Instead, the current code does the opposite: it skips inactive elements and processes active ones. Compare the non-catchall activate callback, which is correct: nft_mapelem_activate(): if (nft_set_elem_active(ext, iter->genmask)) return 0; /* skip active, process inactive */ With the buggy catchall version: nft_map_catchall_activate(): if (!nft_set_elem_active(ext, genmask)) continue; /* skip inactive, process active */ The consequence is that when a DELSET operation is aborted, nft_setelem_data_activate() is never called for the catchall element. For NFT_GOTO verdict elements, this means nft_data_hold() is never called to restore the chain->use reference count. Each abort cycle permanently decrements chain->use. Once chain->use reaches zero, DELCHAIN succeeds and frees the chain while catchall verdict elements still reference it, resulting in a use-after-free. This is exploitable for local privilege escalation from an unprivileged user via user namespaces + nftables on distributions that enable CONFIG_USER_NS and CONFIG_NF_TABLES. Fix by removing the negation so the check matches nft_mapelem_activate(): skip active elements, process inactive ones.

Affected (CNA)

Vendor / product	Versions
Linux / Linux	affected 25aa2ad37c2162be1c0bc4fe6397f7e4c13f00f8 before 8c760ba4e36c750379d13569f23f5a6e185333f5; affected d60be2da67d172aecf866302c91ea11533eca4d9 before b9b6573421de51829f7ec1cce76d85f5f6fbbd7f; affected 628bd3e49cba1c066228e23d71a852c23e26da73 before 42c574c1504aa089a0a142e4c13859327570473d; affected 628bd3e49cba1c066228e23d71a852c23e26da73 before 1444ff890b4653add12f734ffeffc173d42862dd; affected 628bd3e49cba1c066228e23d71a852c23e26da73 before 8b68a45f9722f2babe9e7bad00aa74638addf081; affected 628bd3e49cba1c066228e23d71a852c23e26da73 before f41c5d151078c5348271ffaf8e7410d96f2d82f8; affected bc9f791d2593f17e39f87c6e2b3a36549a3705b1; affected 3c7ec098e3b588434a8b07ea9b5b36f04cef1f50; affected a136b7942ad2a50de708f76ea299ccb45ac7a7f9; affected dc7cdf8cbcbf8b13de1df93f356ec04cdeef5c41; affected 5.15.121 before 5.15.200; affected 6.1.36 before 6.1.163; affected 4.19.316 before 4.20; affected 5.4.262 before 5.5; affected 5.10.188 before 5.11; affected 6.3.10 before 6.4
Linux / Linux	affected 6.4; unaffected 0 before 6.4; unaffected 5.15.200 through 5.15.; unaffected 6.1.163 through 6.1.; unaffected 6.6.124 through 6.6.; unaffected 6.12.70 through 6.12.; unaffected 6.18.10 through 6.18.; unaffected 6.19 through

Vendor / product

Versions

Linux / Linux

affected 25aa2ad37c2162be1c0bc4fe6397f7e4c13f00f8 before 8c760ba4e36c750379d13569f23f5a6e185333f5; affected d60be2da67d172aecf866302c91ea11533eca4d9 before b9b6573421de51829f7ec1cce76d85f5f6fbbd7f; affected 628bd3e49cba1c066228e23d71a852c23e26da73 before 42c574c1504aa089a0a142e4c13859327570473d; affected 628bd3e49cba1c066228e23d71a852c23e26da73 before 1444ff890b4653add12f734ffeffc173d42862dd; affected 628bd3e49cba1c066228e23d71a852c23e26da73 before 8b68a45f9722f2babe9e7bad00aa74638addf081; affected 628bd3e49cba1c066228e23d71a852c23e26da73 before f41c5d151078c5348271ffaf8e7410d96f2d82f8; affected bc9f791d2593f17e39f87c6e2b3a36549a3705b1; affected 3c7ec098e3b588434a8b07ea9b5b36f04cef1f50; affected a136b7942ad2a50de708f76ea299ccb45ac7a7f9; affected dc7cdf8cbcbf8b13de1df93f356ec04cdeef5c41; affected 5.15.121 before 5.15.200; affected 6.1.36 before 6.1.163; affected 4.19.316 before 4.20; affected 5.4.262 before 5.5; affected 5.10.188 before 5.11; affected 6.3.10 before 6.4

Linux / Linux

affected 6.4; unaffected 0 before 6.4; unaffected 5.15.200 through 5.15.*; unaffected 6.1.163 through 6.1.*; unaffected 6.6.124 through 6.6.*; unaffected 6.12.70 through 6.12.*; unaffected 6.18.10 through 6.18.*; unaffected 6.19 through *

CWE

No CWE identifiers supplied.

References

ADP enrichment

siemens-SADP

No English description supplied.

CISA-ADP

No English description supplied.

https://blog.exodusintel.com/2026/06/08/off-by-exploiting-a-use-after-free-in-the-linux-kernel/

redhat-SADP

A flaw was found in the Linux kernel's nf_tables component. A logic bug in nft_map_catchall_activate causes an inverted element activity check during the abort path of a failed transaction. This can lead to a use-after-free vulnerability, as catchall verdict elements may still reference a freed chain. A local low privileged user can exploit this to cause a denial of service or potentially achieve privilege escalation.