CVE-2026-68118: Linux kernel · tcp: challenge ACK for non-exact RST in SYN-RECEIVED
Affects Linux kernelSource CVE Database V5
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
- 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:HExploitation evidence
Disclosed: evidence found.
CVE published 10 Aug 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
|
| LinuxLinux | Affected
| 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
- git.kernel.org/stable/c/8b0a3a094f4cae2fb92e4d08d4eef7246a9d9c49 (opens in a new tab)
- git.kernel.org/stable/c/0fe4636665d14a258de70b4f3e8248e6d42038f1 (opens in a new tab)
- git.kernel.org/stable/c/234f9ffbd9b2c1b24ec67200ea3cff07401bec48 (opens in a new tab)
- git.kernel.org/stable/c/22cec809b048495310f206d9abbcdbbfbdce3ae3 (opens in a new tab)
- git.kernel.org/stable/c/a28c4fcbf774e23b4779cae468e3497a5ad1f4a1 (opens in a new tab)