CVE-2025-40133 mptcp: Use __sk_dst_get() and dst_dev_rcu() in mptcp_active_enable().
A use-after-free vulnerability in the Linux kernel's MPTCP implementation allows attackers to potentially execute code or escalate privileges.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-40133?
CVE-2025-40133 is a high-severity use after free vulnerability in Linux, published on 12 Nov 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
mptcp: Use __sk_dst_get() and dst_dev_rcu() in mptcp_active_enable().
mptcp_active_enable() is called from subflow_finish_connect(), which is icsk->icsk_af_ops->sk_rx_dst_set() and it's not always under RCU.
Using sk_dst_get(sk)->dev could trigger UAF.
Let's use __sk_dst_get() and dst_dev_rcu().
Which versions are affected by CVE-2025-40133?
How do I fix CVE-2025-40133?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2025-40133 being exploited?
There is no known exploitation of CVE-2025-40133 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2025-40133, DEBIAN-CVE-2025-40133, GHSA-q2wv-3qj8-h2hq, ROOT-OS-DEBIAN-13-CVE-2025-40133, UBUNTU-CVE-2025-40133.