CVE-2026-63913: Linux kernel · Improper Input Validation
Affects Linux kernelSource CVE Database V5
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
- 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:HExploitation evidence
Disclosed: evidence found.
CVE published 19 Jul 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by 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
| Product | Affected | Fixed in |
|---|---|---|
| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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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
- git.kernel.org/stable/c/2006979a15af5404bf932a325357683c0bac1656 (opens in a new tab)
- git.kernel.org/stable/c/6476c17d536dbd321c073242e762ddb2713a1238 (opens in a new tab)
- git.kernel.org/stable/c/f5547bebc416d56f56fb5b86dc20aabfa42165a0 (opens in a new tab)
- git.kernel.org/stable/c/2bb6d82b586ea5a4cb73bbdd6b7432e96096bc77 (opens in a new tab)
- git.kernel.org/stable/c/f206def4e86d810f927ba1d8e322ea72b29bce58 (opens in a new tab)
- git.kernel.org/stable/c/b98ab51c45c5608a1c19ce7fd17a3032469bb83f (opens in a new tab)
- git.kernel.org/stable/c/d67c6adee8d1b65330d0174c4c367faba14e80a8 (opens in a new tab)
- git.kernel.org/stable/c/bed6e04be8e6b9133d8b16d5a42d0e0ce674fa9a (opens in a new tab)