CVE-2026-23111
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…
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.49%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
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.
- CVSS 3.1
- 7.8 HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- EPSS
- 0.49% probability · 41th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-416, CWE-672
- Affected
- linux/linux kernel
- Source
- 416baaa9-dc9f-4396-8d5f-8c081fb06d67
References
- https://git.kernel.org/stable/c/1444ff890b4653add12f734ffeffc173d42862ddPatch
- https://git.kernel.org/stable/c/42c574c1504aa089a0a142e4c13859327570473dPatch
- https://git.kernel.org/stable/c/8b68a45f9722f2babe9e7bad00aa74638addf081Patch
- https://git.kernel.org/stable/c/8c760ba4e36c750379d13569f23f5a6e185333f5Patch
- https://git.kernel.org/stable/c/b9b6573421de51829f7ec1cce76d85f5f6fbbd7fPatch
- https://git.kernel.org/stable/c/f41c5d151078c5348271ffaf8e7410d96f2d82f8Patch
- https://access.redhat.com/errata/RHSA-2026:10108
- https://access.redhat.com/errata/RHSA-2026:10996
- https://access.redhat.com/errata/RHSA-2026:18134
- https://access.redhat.com/errata/RHSA-2026:62639
- https://access.redhat.com/errata/RHSA-2026:62641
- https://access.redhat.com/errata/RHSA-2026:6570
- https://access.redhat.com/errata/RHSA-2026:9112
- https://access.redhat.com/security/cve/CVE-2026-23111
- https://blog.exodusintel.com/2026/06/08/off-by-exploiting-a-use-after-free-in-the-linux-kernel/
- https://bugzilla.redhat.com/show_bug.cgi?id=2439687
- https://cert-portal.siemens.com/productcert/html/ssa-019113.html
- https://cert-portal.siemens.com/productcert/html/ssa-082556.html
- https://cert-portal.siemens.com/productcert/html/ssa-253495.html
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-23111.json
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.