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CVE-2026-72247

netfilter: nf_conncount: fix zone comparison in tuple dedup

Published
Last modified
published
Not listed in CISA KEV
Fix
Fixed in 4.15, 5.10.261, 5.15.212, 6.1.178, 6.6.145, and 3 more
None on Exploit-DB, Metasploit or GitHub
  • Exploitation: none
  • Automatable: yes
  • Technical impact: partial

Summary

In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_conncount: fix zone comparison in tuple dedup The "already exists" dedup logic in __nf_conncount_add() decides whether a connection has already been counted and can be skipped instead of incrementing the connlimit count. It compares the conntrack zone of a list entry with the zone of the connection being added using nf_ct_zone_id() and nf_ct_zone_equal(), passing conn->zone.dir or zone->dir as the direction argument. Those helpers take enum ip_conntrack_dir values: IP_CT_DIR_ORIGINAL is 0 and IP_CT_DIR_REPLY is 1. However, zone->dir is a u8 bitmask: NF_CT_ZONE_DIR_ORIG is 1, NF_CT_ZONE_DIR_REPL is 2 and NF_CT_DEFAULT_ZONE_DIR is 3. Passing that bitmask as the enum direction shifts the meaning of every non-zero value. An ORIG-only zone passes 1 and is tested as REPLY, while REPL-only and default zones pass 2 or 3 and test bits beyond the valid direction range. In those cases nf_ct_zone_id() can fall back to NF_CT_DEFAULT_ZONE_ID instead of using the real zone id, so different zones can be treated as equal and dedup collapses to tuple equality alone. nf_conncount stores and compares the original-direction tuple for a connection. If an skb already has an attached conntrack entry, get_ct_or_tuple_from_skb() explicitly copies ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple, regardless of the packet's ctinfo. Therefore the zone comparison in the tuple dedup path must use IP_CT_DIR_ORIGINAL as well; the zone direction bitmask describes where a zone id applies, not which direction this conncount tuple represents. Fix the two dedup comparisons by passing IP_CT_DIR_ORIGINAL directly. Do not special-case NF_CT_DEFAULT_ZONE_DIR and do not compare raw zone ids: using the existing helpers with IP_CT_DIR_ORIGINAL preserves the direction-aware NF_CT_DEFAULT_ZONE_ID fallback. A default bidirectional zone contains the ORIG bit, so it naturally returns the real zone id; reply-only zones continue to fall back for original-direction tuple comparisons.

Timeline

  1. CVE published
  2. CISA SSVC assessment

    Exploitation: none · Automatable: yes · Technical impact: partial

  3. Record last updated

Affected versions

  • Linux Linux

    From 21ba8847f857028dc83a0f341e16ecc616e34740 · fixed in 82fc35e0da9a91db9a034f8311f18f77a599ae3f; From 21ba8847f857028dc83a0f341e16ecc616e34740 · fixed in 78b5d6dbc860776161f9e9206b06ff8a01f531ab; From 21ba8847f857028dc83a0f341e16ecc616e34740 · fixed in 4f30a89c0ed2418719a1144881c2635b940b543d; From 21ba8847f857028dc83a0f341e16ecc616e34740 · fixed in 7bdc3c0985ecf17b957811fedcc684acdf698acc; From 21ba8847f857028dc83a0f341e16ecc616e34740 · fixed in 35a56e2a46b90e6bd4ca816b80e9cb8d20dfc3ce; From 21ba8847f857028dc83a0f341e16ecc616e34740 · fixed in 3cd9a5792cbea81139c24320986dd0db69e9b5d0; From 21ba8847f857028dc83a0f341e16ecc616e34740 · fixed in 6ff07ac5405bea4d4ead3559fc123f987576424a; From 21ba8847f857028dc83a0f341e16ecc616e34740 · fixed in f62c41b4910e65da396ec9a8c40c1fe7fe82e449; From 4.14.92 · fixed in 4.15

  • Linux Linux

    4.18

  • KernelLinux

    From 4.18.0 · fixed in 5.10.261; From 5.11.0 · fixed in 5.15.212; From 5.16.0 · fixed in 6.1.178; From 6.2.0 · fixed in 6.6.145; From 6.7.0 · fixed in 6.12.97; From 6.13.0 · fixed in 6.18.40; From 6.19.0 · fixed in 7.1.5

References 8

git.kernel.org