CVE-2025-21640: sctp: sysctl: cookie_hmac_alg: avoid using current->nsproxy

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-01-19 · updated 2026-10-15
Weakness: CWE-476

Description

In the Linux kernel, the following vulnerability has been resolved: sctp: sysctl: cookie_hmac_alg: 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.sctp_hmac_alg' is used.

Affected products

Linux kernel: from 3.8 before 6.1.125; from 6.2 before 6.6.72; from 6.7 before 6.12.10; 6.13-rc1, 6.13-rc2, 6.13-rc3, 6.13-rc4, 6.13-rc5, 6.13-rc6 — fixed in 6.1.125, 6.12.10, 6.6.72

How to fix

Upgrade to a fixed version: Linux kernel 6.1.125, 6.12.10, 6.6.72. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2025-21640 or the next vulnerability affects your stack