CVE-2026-72247: Linux Vulnerability (CVSS 7.5)

Description

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.

Metrics

CVSS 3.1

7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS Probability

0.21%

11.6th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Linux	Linux	>= 21ba8847f857028dc83a0f341e16ecc616e34740, < 82fc35e0da9a91db9a034f8311f18f77a599ae3f; >= 21ba8847f857028dc83a0f341e16ecc616e34740, < 78b5d6dbc860776161f9e9206b06ff8a01f531ab; >= 21ba8847f857028dc83a0f341e16ecc616e34740, < 4f30a89c0ed2418719a1144881c2635b940b543d; >= 21ba8847f857028dc83a0f341e16ecc616e34740, < 7bdc3c0985ecf17b957811fedcc684acdf698acc; >= 21ba8847f857028dc83a0f341e16ecc616e34740, < 35a56e2a46b90e6bd4ca816b80e9cb8d20dfc3ce; >= 21ba8847f857028dc83a0f341e16ecc616e34740, < 3cd9a5792cbea81139c24320986dd0db69e9b5d0; >= 21ba8847f857028dc83a0f341e16ecc616e34740, < 6ff07ac5405bea4d4ead3559fc123f987576424a; >= 21ba8847f857028dc83a0f341e16ecc616e34740, < f62c41b4910e65da396ec9a8c40c1fe7fe82e449; 525e1dffed8711973f77412729621098a95238e5; 75af3d78168e654a5cd8bbc4c774f97be836165f; >= 4.14.92, < 4.15
Linux	Linux	4.18

References

Timeline

Published: Aug 15, 2026
Last Modified: Aug 17, 2026
Status: Received

Frequently Asked Questions

What is CVE-2026-72247?

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.

How severe is CVE-2026-72247?

CVE-2026-72247 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 0.21% probability of exploitation in the next 30 days.

How do I fix CVE-2026-72247?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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