CVE-2021-47132: mptcp: fix sk_forward_memory corruption on retransmission

Severity: high (CVSS 7.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-03-15 · updated 2026-08-04
Weakness: CWE-787

Description

In the Linux kernel, the following vulnerability has been resolved: mptcp: fix sk_forward_memory corruption on retransmission MPTCP sk_forward_memory handling is a bit special, as such field is protected by the msk socket spin_lock, instead of the plain socket lock. Currently we have a code path updating such field without handling the relevant lock: __mptcp_retrans() -> __mptcp_clean_una_wakeup() Several helpers in __mptcp_clean_una_wakeup() will update sk_forward_alloc, possibly causing such field corruption, as reported by Matthieu. Address the issue providing and using a new variant of blamed function which explicitly acquires the msk spin lock.

Affected products

Linux kernel: from 5.12 before 5.12.10; 5.13-rc1, 5.13-rc2, 5.13-rc3, 5.13-rc4 — fixed in 5.12.10

How to fix

Upgrade to a fixed version: Linux kernel 5.12.10. Check the vendor advisory for mitigations.

References

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