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VulnerabilityPublished Updated

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

Source GCVE Database

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Authoritative record:CVE-2026-68118· High 8.2

Not known to be exploited · CVSS 8.2 High · fixed in c5dc463cc60eb26079b19607c9dbda76491dad05 : patch Linux kernel soon.

Data as of 30 Oct 2026, 16:33 UTC

CVSS 3.1 base score
8.2High
How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none
CVSS scores by source
CNA (Linux)CVSS 3.18.2
Patch
Available – fixed in c5dc463cc60eb26079b19607c9dbda76491dad05, a28c4fcbf774e23b4779cae468e3497a5ad1f4a1, 234f9ffbd9b2c1b24ec67200ea3cff07401bec48 +6
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. Weaponized: 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 30 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
  • c5dc463cc60eb26079b19607c9dbda76491dad05
  • 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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