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VulnerabilityPublished Updated

CVE-2026-63913: Linux kernel · Improper Input Validation

Affects Linux kernelSource CVE Database V5

0

Not known to be exploited · CVSS 8.2 High · fixed in f5547bebc416d56f56fb5b86dc20aabfa42165a0 : patch Linux kernel soon.

Data as of 26 Oct 2026, 14:05 UTC

CVSS 3.1 base score
8.2High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.9% chance of exploitation in 30 days – higher than 61% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CISA SSVC
Exploitation
No evidence of active exploitation and no public proof of concept
Automatable
Attackers can reliably automate steps 1–4 of the kill chain
Technical impact
Limited control over the software or limited information exposure

CISA SSVC assessment, 2026-10-16.

Patch
Available – fixed in f5547bebc416d56f56fb5b86dc20aabfa42165a0, f206def4e86d810f927ba1d8e322ea72b29bce58, d67c6adee8d1b65330d0174c4c367faba14e80a8 +5
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 19 Jul 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

ProductAffectedFixed in
LinuxLinuxAffected
  • ≥ 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1, < f5547bebc416d56f56fb5b86dc20aabfa42165a0
Fixed in
  • f5547bebc416d56f56fb5b86dc20aabfa42165a0
LinuxLinuxAffected
  • ≥ 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1, < f206def4e86d810f927ba1d8e322ea72b29bce58
Fixed in
  • f206def4e86d810f927ba1d8e322ea72b29bce58
LinuxLinuxAffected
  • ≥ 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1, < d67c6adee8d1b65330d0174c4c367faba14e80a8
Fixed in
  • d67c6adee8d1b65330d0174c4c367faba14e80a8
LinuxLinuxAffected
  • ≥ 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1, < bed6e04be8e6b9133d8b16d5a42d0e0ce674fa9a
Fixed in
  • bed6e04be8e6b9133d8b16d5a42d0e0ce674fa9a
LinuxLinuxAffected
  • ≥ 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1, < b98ab51c45c5608a1c19ce7fd17a3032469bb83f
Fixed in
  • b98ab51c45c5608a1c19ce7fd17a3032469bb83f
LinuxLinuxAffected
  • ≥ 9fb9cbb1082d6b31fb45aa1a14432449a0df6cf1, < 2006979a15af5404bf932a325357683c0bac1656
Fixed in
  • 2006979a15af5404bf932a325357683c0bac1656

Description

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.

References

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