CVE-2026-63913: Linux

High severity, CVSS 8.2. EPSS: 1% chance of exploitation in the next 30 days.

In the Linux kernel, the following vulnerability has been resolved: netfilter: conntrack: tcp: do not force CLOSE on invalid-seq RST without direction check An unintended behavior in the TCP conntrack state machine allows a connection to be forced into the CLOSE state using an RST packet with an invalid sequence number. Specifically, after a SYN packet is observed, an RST with an invalid SEQ can transition the conntrack entry to TCP_CONNTRACK_CLOSE, regardless of whether the RST corresponds to the expected reply direction. The relevant code path assumes the RST is a response to an outgoing SYN, but does not validate packet direction or ensure that a matching SYN was actually sent in the opposite direction. As a result, a crafted packet sequence consisting of a SYN followed by an invalid-sequence RST can prematurely terminate an active NAT entry. This makes connection teardown easier than intended. So, tighten the state transition logic to ensure that RST-triggered CLOSE transitions only occur when the RST is a valid response to a previously observed SYN in the correct direction.

Affected products

• Linux Linux: from 2.6.15, before 5.10.259 (fixed in 5.10.259); from 5.11, before 5.15.210 (fixed in 5.15.210); from 5.16, before 6.1.176 (fixed in 6.1.176); from 6.2, before 6.6.143 (fixed in 6.6.143); from 6.7, before 6.12.93 (fixed in 6.12.93); from 6.13, before 6.18.35 (fixed in 6.18.35); …

Published 2026-07-19. Last modified 2026-07-27.