CVE-2025-40139 smc: Use __sk_dst_get() and dst_dev_rcu() in in smc_clc_prfx_set().
A use-after-free vulnerability in the Linux kernel's SMC protocol allows attackers to potentially execute code or cause a denial of service during connection setup.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-40139?
CVE-2025-40139 is a high-severity use after free vulnerability in Linux, published on 12 Nov 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
smc: Use __sk_dst_get() and dst_dev_rcu() in in smc_clc_prfx_set().
smc_clc_prfx_set() is called during connect() and not under RCU nor RTNL.
Using sk_dst_get(sk)->dev could trigger UAF.
Let's use __sk_dst_get() and dev_dst_rcu() under rcu_read_lock() after kernel_getsockname().
Note that the returned value of smc_clc_prfx_set() is not used in the caller.
While at it, we change the 1st arg of smc_clc_prfx_set[46]_rcu() not to touch dst there.
Which versions are affected by CVE-2025-40139?
How do I fix CVE-2025-40139?
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-2025-40139 being exploited?
There is no known exploitation of CVE-2025-40139 in the wild and no public exploit code.
Sources
Also known as AZL-69998, BELL-CVE-2025-40139, DEBIAN-CVE-2025-40139, GHSA-ffj5-vpjf-2hxm, ROOT-OS-DEBIAN-11-CVE-2025-40139, ROOT-OS-DEBIAN-12-CVE-2025-40139 and 4 more.