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CVE-2026-72418

netfilter: nf_conncount: prevent connlimit drops for early confirmed ct

Published
Last modified
published
Not listed in CISA KEV
Fix
Fixed in 5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.97, 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: 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.

Timeline

  1. CVE published
  2. CISA SSVC assessment

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

  3. Record last updated

Affected versions

  • Linux Linux

    From 460c112e1d887b58b06b56e8e0230058906ff2c3 · fixed in 000ac6830b56499d6b65fd91486ce6689eb02be4; From 53bc0ac47f4f7621c991807bc90e01df49561ac8 · fixed in cbe2d14a7c5b1fc71821fbfee5c4963917411e92; From ca8b4d1d6304a84ce2016fa2fe9a114b9607b839 · fixed in 3793d24de224943e0a6016bbeffb6f5c4cea2e3d; From 8286c02fe9100330475331253fc590f047963f90 · fixed in abef7f817217fcb62c11821d6b895063eadb2828; From b29ddccf36946a90323486221f39e9f88cc01b8e · fixed in ebfe8249ba79e4ff0f1e3aad8787b992ef27f026; From 77ea3d8ac3d3d59b5ac9ad639e4ba107c0f2ff1e · fixed in 329f2626ee5cb8fafdf6b58b624311529c57cb45; From 69894e5b4c5e28cda5f32af33d4a92b7a4b93b0e · fixed in be52572c6d55f677ba76869d3c63805c0d4891a3; From 69894e5b4c5e28cda5f32af33d4a92b7a4b93b0e · fixed in c8b6f36f766991e3ebebec6596daee4b04dcbc49; From 5.10.248 · fixed in 5.10.261; From 5.15.198 · fixed in 5.15.212; From 6.1.160 · fixed in 6.1.178; From 6.6.120 · fixed in 6.6.145; From 6.12.63 · fixed in 6.12.97; From 6.18.2 · fixed in 6.18.40; From 6.17.13 · fixed in 6.18

  • Linux Linux

    6.19

  • KernelLinux

    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