CVE-2025-21641 mptcp: sysctl: blackhole timeout: avoid using current->nsproxy

What is CVE-2025-21641?

CVE-2025-21641 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:

mptcp: sysctl: blackhole timeout: avoid using current->nsproxy

As mentioned in the previous commit, 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 'pernet' structure can be obtained from the table->data using container_of().

Weakness: CWE-476

Which versions are affected by CVE-2025-21641?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2025-21641?

Apply the vendor's patch.

Is CVE-2025-21641 being exploited?

There is no known exploitation of CVE-2025-21641 in the wild and no public exploit code.

Other vulnerabilities in Linux kernel

• CVE-2026-53266 Linux Kernel Out-of-Bounds Write Exploited High 8.8
• CVE-2013-6282 Linux Kernel Improper Input Validation Exploited High 8.8
• CVE-2022-0185 Linux Kernel Heap-Based Buffer Overflow Exploited High 8.4
• CVE-2013-2094 Linux Kernel Privilege Escalation Exploited High 8.4
• CVE-2026-53362 Linux Kernel Unspecified Exploited High 7.8

All Linux kernel vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as BELL-CVE-2025-21641, DEBIAN-CVE-2025-21641, GHSA-74ff-8pv9-crm9, UBUNTU-CVE-2025-21641.