CVE-2026-63913 Affecting kernel-rt-modules package, versions <0:4.18.0-553.158.1.rt7.499.el8_10


Severity

Recommended
high

Based on AlmaLinux security rating.

Threat Intelligence

EPSS
0.97% (60th percentile)

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  • Snyk IDSNYK-ALMALINUX8-KERNELRTMODULES-19276914
  • published27 Aug 2026
  • disclosed26 Aug 2026

Introduced: 26 Aug 2026

NewCVE-2026-63913  (opens in a new tab)

How to fix?

Upgrade AlmaLinux:8 kernel-rt-modules to version 0:4.18.0-553.158.1.rt7.499.el8_10 or higher.
This issue was patched in ALSA-2026:59737.

NVD Description

Note: Versions mentioned in the description apply only to the upstream kernel-rt-modules package and not the kernel-rt-modules package as distributed by AlmaLinux. See How to fix? for AlmaLinux:8 relevant fixed versions and status.

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.

CVSS Base Scores

version 3.1