CVE-2026-72247: netfilter: nf_conncount: fix zone comparison in tuple dedup
In the Linux kernel, the following vulnerability has been resolved:
netfilter: nfconncount: fix zone comparison in tuple dedup
The "already exists" dedup logic in nfconncountadd() 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 nfctzoneid() and nfctzoneequal(), passing conn->zone.dir or zone->dir as the direction argument.
Those helpers take enum ipconntrackdir values: IPCTDIRORIGINAL is 0 and IPCTDIRREPLY is 1. However, zone->dir is a u8 bitmask: NFCTZONEDIRORIG is 1, NFCTZONEDIRREPL is 2 and NFCTDEFAULTZONEDIR 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 nfctzoneid() can fall back to NFCTDEFAULTZONEID instead of using the real zone id, so different zones can be treated as equal and dedup collapses to tuple equality alone.
nfconncount stores and compares the original-direction tuple for a connection. If an skb already has an attached conntrack entry, getctortuplefromskb() explicitly copies ct->tuplehash[IPCTDIRORIGINAL].tuple, regardless of the packet's ctinfo. Therefore the zone comparison in the tuple dedup path must use IPCTDIRORIGINAL 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 IPCTDIRORIGINAL directly. Do not special-case NFCTDEFAULTZONEDIR and do not compare raw zone ids: using the existing helpers with IPCTDIRORIGINAL preserves the direction-aware NFCTDEFAULTZONEID 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.
Affected Software
Remediation
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In the __nf_conncount_add() tuple-dedup path, fix both zone comparisons by passing IP_CT_DIR_ORIGINAL directly to nf_ct_zone_id() and nf_ct_zone_equal(), rather than passing conn->zone.dir or zone->dir.
Event History
Frequently Asked Questions
What is the severity of CVE-2026-72247?
CVE-2026-72247 has a risk level assigned as 37.
What systems are affected by CVE-2026-72247?
CVE-2026-72247 affects the Linux kernel implementations that utilize the netfilter nf_conncount feature.
How do I fix CVE-2026-72247?
To fix CVE-2026-72247, you should update your Linux kernel to the patched version that resolves the vulnerability.
What impact does CVE-2026-72247 have if exploited?
Exploitation of CVE-2026-72247 can lead to incorrect connection count behavior, affecting the connlimit functionality.
Is there any workaround for CVE-2026-72247 before applying patches?
There are no specific workarounds for CVE-2026-72247; applying the kernel update is the recommended action.