CVE-2025-21639 sctp: sysctl: rto_min/max: avoid using current->nsproxy
A null pointer dereference in the Linux kernel SCTP subsystem can cause a system crash when specific network namespace conditions are met.
- 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-2025-21639?
CVE-2025-21639 is a medium-severity vulnerability in Linux kernel, published on 19 Jan 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:
sctp: sysctl: rto_min/max: avoid using current->nsproxy
As mentioned in a previous commit of this series, using the 'net' structure via 'current' is not recommended for different reasons:
- Inconsistency: getting info from the reader's/writer's netns vs only from the opener's netns.
- current->nsproxy can be NULL in some cases, resulting in an 'Oops' (null-ptr-deref), e.g. when the current task is exiting, as spotted by syzbot [1] using acct(2).
The 'net' structure can be obtained from the table->data using container_of().
Note that table->data could also be used directly, as this is the only member needed from the 'net' structure, but that would increase the size of this fix, to use '*data' everywhere 'net->sctp.rto_min/max' is used.
Weakness: CWE-476
Which versions are affected by CVE-2025-21639?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-21639?
Apply the vendor's patch.
Is CVE-2025-21639 being exploited?
There is no known exploitation of CVE-2025-21639 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-57225, BELL-CVE-2025-21639, DEBIAN-CVE-2025-21639, GHSA-6w8c-3g24-p9jh, UBUNTU-CVE-2025-21639.