Bug 2425184 (CVE-2023-54085)

Summary: CVE-2023-54085 kernel: Linux kernel: Denial of Service due to NULL pointer dereference in mptcp fastopen
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in the Linux kernel's Multipath TCP (mptcp) implementation. During an early fallback to TCP in the fastopen process, the system incorrectly deletes a subflow context before it is no longer needed. This can lead to a NULL pointer dereference, allowing a local attacker with low privileges to cause a Denial of Service (DoS) by crashing the system.
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Description OSIDB Bzimport 2025-12-24 14:09:15 UTC 
In the Linux kernel, the following vulnerability has been resolved:

mptcp: fix NULL pointer dereference on fastopen early fallback

In case of early fallback to TCP, subflow_syn_recv_sock() deletes
the subflow context before returning the newly allocated sock to
the caller.

The fastopen path does not cope with the above unconditionally
dereferencing the subflow context.
Comment 1 Alexander B 2025-12-24 20:18:49 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025122405-CVE-2023-54085-7e32@gregkh/T