CVE-2026-72418
HighCVSS 7.5Exploitation Probability (EPSS)
Elevated risk51th percentile - higher than 51% of all known CVEs
Summary
A vulnerability in the Linux kernel's netfilter (nf_conncount) causes incorrect packet drops for valid connections when using connlimit in soft-limiting scenarios. The issue occurs when a new connection reuses a socket in TIME_WAIT state, where the connection tracking entry is mistakenly treated as confirmed, leading to a zeroed active connection count and false rejection of traffic. The fix replaces the loopback interface check with protocol-agnostic state checks (IPS_ASSURED), allowing early-confirmed setup packets to be properly evaluated and counted.
Risk Assessment
Organizations using iptables/nftables rules with connlimit (e.g., for DoS protection) may experience blocking of legitimate network traffic, leading to service unavailability. Systems with high volumes of connections reusing TIME_WAIT sockets are particularly affected.
Recommendation
Urgently update the Linux kernel to a version containing the fix for CVE-2026-72418 and test connlimit rules after the update. If updating is not possible, consider temporarily disabling connlimit rules or increasing limits to minimize false drops.
Original NVD description (English source)
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.