High 8.2Published Aug 10, 2026

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

Updated under an hour ago (Oct 27, 2026, 5:00 PM ET)

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Exploited in the last 30 days

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.

CVSS: 8.2 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H
Weakness (CWE): CWE-20
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: Linux
NVD analysis: Received
Record last updated: Oct 19, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

Linux Linux linux:linux (from the name)	282f23c6ee343126156dd41218b22ece96d747e3 builds before 8b0a3a094f4cae2fb92e4d08d4eef7246a9d9c49; 282f23c6ee343126156dd41218b22ece96d747e3 builds before 0fe4636665d14a258de70b4f3e8248e6d42038f1; 282f23c6ee343126156dd41218b22ece96d747e3 builds before 234f9ffbd9b2c1b24ec67200ea3cff07401bec48; 282f23c6ee343126156dd41218b22ece96d747e3 builds before 22cec809b048495310f206d9abbcdbbfbdce3ae3; from 282f23c6ee343126156dd41218b22ece96d747e3 before a28c4fcbf774e23b4779cae468e3497a5ad1f4a1; 86791bbfe5ed7b275be040cfeff049a1624af1b7; 61f69dc4e40e41b0018f00fa4aeb23d3239556fb; 34fb350281ced2a72707a5c0064f69992d440edb; and 3 more ranges	CNA record

References

References

https://git.kernel.org/stable/c/8b0a3a094f4cae2fb92e4d08d4eef7246a9d9c49
https://git.kernel.org/stable/c/0fe4636665d14a258de70b4f3e8248e6d42038f1
https://git.kernel.org/stable/c/234f9ffbd9b2c1b24ec67200ea3cff07401bec48
https://git.kernel.org/stable/c/22cec809b048495310f206d9abbcdbbfbdce3ae3
https://git.kernel.org/stable/c/a28c4fcbf774e23b4779cae468e3497a5ad1f4a1

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.