CVE-2026-53243: rseq: Fix using an uninitialized stack variable in rseq_exit_user_update()

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-06-25 · updated 2026-07-07
Weakness: CWE-908

Description

In the Linux kernel, the following vulnerability has been resolved: rseq: Fix using an uninitialized stack variable in rseq_exit_user_update() There is an bug in which an uninitialized stack variable is used in rseq_exit_user_update() as reported by syzbot: BUG: KMSAN: kernel-infoleak in rseq_set_ids_get_csaddr include/linux/rseq_entry.h:502 [inline] The local variable: struct rseq_ids ids = { .cpu_id = task_cpu(t), .mm_cid = task_mm_cid(t), .node_id = cpu_to_node(ids.cpu_id), }; According to the C standard, the evaluation order of expressions in an initializer list is indeterminately sequenced. The compiler (Clang, in this KMSAN build) evaluates `cpu_to_node(ids.cpu_id)` *before* `ids.cpu_id` is initialized with `task_cpu(t)`. This is fixed by moving the assignment of ids.node_id outside the structure initialization.

Affected products

Linux kernel: from 7.0.10 before 7.0.13; 7.1-rc3, 7.1-rc4, 7.1-rc5, 7.1-rc6 — fixed in 7.0.13

How to fix

Upgrade to a fixed version: Linux kernel 7.0.13. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2026-53243 or the next vulnerability affects your stack