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VulnerabilityPublished Updated

CVE-2026-68118: Linux kernel · tcp: challenge ACK for non-exact RST in SYN-RECEIVED

Affects Linux kernelSource CVE Database V5

0

Not known to be exploited · CVSS 8.2 High · fixed in a28c4fcbf774e23b4779cae468e3497a5ad1f4a1 : patch Linux kernel soon.

Data as of 26 Oct 2026, 17:30 UTC

CVSS 3.1 base score
8.2High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.3% chance of exploitation in 30 days – higher than 33% 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 a28c4fcbf774e23b4779cae468e3497a5ad1f4a1, 234f9ffbd9b2c1b24ec67200ea3cff07401bec48, 22cec809b048495310f206d9abbcdbbfbdce3ae3 +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 10 Aug 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
  • >=3.0.58 <3.1
  • >=3.2.37 <3.3
  • >=3.4.25 <3.5
Fixed in
  • a28c4fcbf774e23b4779cae468e3497a5ad1f4a1
  • 234f9ffbd9b2c1b24ec67200ea3cff07401bec48
  • 22cec809b048495310f206d9abbcdbbfbdce3ae3
  • 8b0a3a094f4cae2fb92e4d08d4eef7246a9d9c49
  • 3.5
  • 3.3
  • 3.1
  • 0fe4636665d14a258de70b4f3e8248e6d42038f1
LinuxLinuxAffected
  • =3.6
Fixed in–

Description

In the Linux kernel, the following vulnerability has been resolved: tcp: challenge ACK for non-exact RST in SYN-RECEIVED The SYN-RECEIVED request-socket path in tcp_check_req() accepts an in-window RST without requiring SEG.SEQ to exactly match RCV.NXT. A non-exact RST therefore removes the request instead of eliciting a challenge ACK. RFC 9293 section 3.10.7.4 applies the RFC 5961 reset check in SYN-RECEIVED: an exact RST resets the connection, while a non-exact in-window RST must trigger a challenge ACK and be dropped. Apply that check before the ACK-field validation, following the RFC sequence-number, RST, then ACK processing order. Factor the per-netns challenge ACK quota out of tcp_send_challenge_ack() so request sockets can share it. Use the request socket's send_ack() callback and its own out-of-window ACK timestamp to send and rate-limit the response.

References

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