CVE-2024-40931: mptcp: ensure snd_una is properly initialized on connect

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-07-12 · updated 2026-06-17
Weakness: CWE-908

Description

In the Linux kernel, the following vulnerability has been resolved: mptcp: ensure snd_una is properly initialized on connect This is strictly related to commit fb7a0d334894 ("mptcp: ensure snd_nxt is properly initialized on connect"). It turns out that syzkaller can trigger the retransmit after fallback and before processing any other incoming packet - so that snd_una is still left uninitialized. Address the issue explicitly initializing snd_una together with snd_nxt and write_seq.

Affected products

Linux kernel: from 5.9 before 5.10.221; from 5.11 before 5.15.162; from 5.16 before 6.1.95; from 6.2 before 6.6.35; from 6.7 before 6.9.6; 6.10-rc1, 6.10-rc2, 6.10-rc3 — fixed in 5.10.221, 5.15.162, 6.1.95, 6.6.35, 6.9.6

How to fix

Upgrade to a fixed version: Linux kernel 5.10.221, 5.15.162, 6.1.95, 6.6.35. Check the vendor advisory for mitigations.

References

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