CVE-2025-38552: mptcp: plug races between subflow fail and subflow creation

Severity: high (CVSS 7.8 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: 2025-08-16 · updated 2026-10-15

Description

In the Linux kernel, the following vulnerability has been resolved: mptcp: plug races between subflow fail and subflow creation We have races similar to the one addressed by the previous patch between subflow failing and additional subflow creation. They are just harder to trigger. The solution is similar. Use a separate flag to track the condition 'socket state prevent any additional subflow creation' protected by the fallback lock. The socket fallback makes such flag true, and also receiving or sending an MP_FAIL option. The field 'allow_infinite_fallback' is now always touched under the relevant lock, we can drop the ONCE annotation on write.

Affected products

Debian Linux: 11.0
Linux kernel: from 5.15 before 6.1.149; from 6.2 before 6.6.101; from 6.7 before 6.12.40; from 6.13 before 6.15.8; 6.16-rc1, 6.16-rc2, 6.16-rc3, 6.16-rc4, 6.16-rc5, 6.16-rc6 — fixed in 6.1.149, 6.12.40, 6.15.8, 6.6.101

How to fix

Upgrade to a fixed version: Linux kernel 6.1.149, 6.12.40, 6.15.8, 6.6.101. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2025-38552 or the next vulnerability affects your stack