CVE-2025-71080: ipv6: fix a BUG in rt6_get_pcpu_route() under PREEMPT_RT

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-01-13 · updated 2026-07-30
Weakness: CWE-617

Description

In the Linux kernel, the following vulnerability has been resolved: ipv6: fix a BUG in rt6_get_pcpu_route() under PREEMPT_RT On PREEMPT_RT kernels, after rt6_get_pcpu_route() returns NULL, the current task can be preempted. Another task running on the same CPU may then execute rt6_make_pcpu_route() and successfully install a pcpu_rt entry. When the first task resumes execution, its cmpxchg() in rt6_make_pcpu_route() will fail because rt6i_pcpu is no longer NULL, triggering the BUG_ON(prev). It's easy to reproduce it by adding mdelay() after rt6_get_pcpu_route(). Using preempt_disable/enable is not appropriate here because ip6_rt_pcpu_alloc() may sleep. Fix this by handling the cmpxchg() failure gracefully on PREEMPT_RT: free our allocation and return the existing pcpu_rt installed by another task. The BUG_ON is replaced by WARN_ON_ONCE for non-PREEMPT_RT kernels where such races should not occur.

Affected products

Linux kernel: from 6.12.1 before 6.12.64; from 6.13 before 6.18.4; 6.12, 6.19-rc1, 6.19-rc2, 6.19-rc3, 6.19-rc4, 6.19-rc5 (+3) — fixed in 6.12.64, 6.18.4

How to fix

Upgrade to a fixed version: Linux kernel 6.12.64, 6.18.4. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2025-71080 or the next vulnerability affects your stack