CVE-2026-72418

Summary

In the Linux kernel, the following vulnerability has been resolved:

netfilter: nf_conncount: prevent connlimit drops for early confirmed ct

Commit 69894e5b4c5e ("netfilter: nft_connlimit: update the count if add was skipped") introduced a regression where packets for valid connections are dropped when using connlimit for soft-limiting scenarios.

The issue occurs when a new connection reuses a socket currently in the TIME_WAIT state. In this scenario, the connection tracking entry is evaluated as already confirmed. Previously, __nf_conncount_add() assumed that if a connection was confirmed and did not originate from the loopback interface, it should skip the addition and return -EEXIST.

Skipping the addition triggers a garbage collection run that cleans up the TIME_WAIT connection. Consequently, the active connection count drops to 0, which xt_connlimit mishandles, leading to the false rejection of the perfectly valid new connection.

Fix this by replacing the interface check with protocol-agnostic state checks. We now skip the tree insertion and preserve the lockless garbage collection optimization only if the connection is IPS_ASSURED. This allows early-confirmed setup packets (such as reused TIME_WAIT sockets or locally generated SYN-ACKs) to be properly evaluated and counted without falsely dropping. The goto check_connections path is maintained to ensure these setup packets are deduplicated correctly.

This has been tested with slowhttptest and HTTP server configured locally to ensure we are not breaking soft-limiting scenarios for local or external connections. In addition, it was tested with a OVS zone limit too.

Affected Software

VendorProductVersion RangeStatus
LinuxLinux460c112e1d887b58b06b56e8e0230058906ff2c3 < 000ac6830b56499d6b65fd91486ce6689eb02be4affected
LinuxLinux53bc0ac47f4f7621c991807bc90e01df49561ac8 < cbe2d14a7c5b1fc71821fbfee5c4963917411e92affected
LinuxLinuxca8b4d1d6304a84ce2016fa2fe9a114b9607b839 < 3793d24de224943e0a6016bbeffb6f5c4cea2e3daffected
LinuxLinux8286c02fe9100330475331253fc590f047963f90 < abef7f817217fcb62c11821d6b895063eadb2828affected
LinuxLinuxb29ddccf36946a90323486221f39e9f88cc01b8e < ebfe8249ba79e4ff0f1e3aad8787b992ef27f026affected
LinuxLinux77ea3d8ac3d3d59b5ac9ad639e4ba107c0f2ff1e < 329f2626ee5cb8fafdf6b58b624311529c57cb45affected
LinuxLinux69894e5b4c5e28cda5f32af33d4a92b7a4b93b0e < be52572c6d55f677ba76869d3c63805c0d4891a3affected
LinuxLinux69894e5b4c5e28cda5f32af33d4a92b7a4b93b0e < c8b6f36f766991e3ebebec6596daee4b04dcbc49affected
LinuxLinuxf85623af16b83615e5f64a9b19ae1d584805cb07affected
LinuxLinux5.10.248 < 5.10.261affected
LinuxLinux5.15.198 < 5.15.212affected
LinuxLinux6.1.160 < 6.1.178affected
LinuxLinux6.6.120 < 6.6.145affected
LinuxLinux6.12.63 < 6.12.97affected
LinuxLinux6.18.2 < 6.18.40affected
LinuxLinux6.17.13 < 6.18affected
LinuxLinux6.19affected
LinuxLinux0 < 6.19unaffected
LinuxLinux5.10.261 <= 5.10.*unaffected
LinuxLinux5.15.212 <= 5.15.*unaffected
LinuxLinux6.1.178 <= 6.1.*unaffected
LinuxLinux6.6.145 <= 6.6.*unaffected
LinuxLinux6.12.97 <= 6.12.*unaffected
LinuxLinux6.18.40 <= 6.18.*unaffected
LinuxLinux7.1.5 <= 7.1.*unaffected
LinuxLinux7.2 <= *unaffected

Weaknesses

References