CVE-2023-53728 posix-timers: Ensure timer ID search-loop limit is valid

What is CVE-2023-53728?

CVE-2023-53728 is a vulnerability in Linux, published on 22 Oct 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:

posix-timers: Ensure timer ID search-loop limit is valid

posix_timer_add() tries to allocate a posix timer ID by starting from the cached ID which was stored by the last successful allocation.

This is done in a loop searching the ID space for a free slot one by one. The loop has to terminate when the search wrapped around to the starting point.

But that's racy vs. establishing the starting point. That is read out lockless, which leads to the following problem:

CPU0 CPU1 posix_timer_add() start = sig->posix_timer_id; lock(hash_lock); ... posix_timer_add() if (++sig->posix_timer_id < 0) start = sig->posix_timer_id; sig->posix_timer_id = 0;

So CPU1 can observe a negative start value, i.e. -1, and the loop break never happens because the condition can never be true:

if (sig->posix_timer_id == start) break;

While this is unlikely to ever turn into an endless loop as the ID space is huge (INT_MAX), the racy read of the start value caught the attention of KCSAN and Dmitry unearthed that incorrectness.

Rewrite it so that all id operations are under the hash lock.

Which versions are affected by CVE-2023-53728?

How do I fix CVE-2023-53728?

Apply the vendor's patch.

Is CVE-2023-53728 being exploited?

There is no known exploitation of CVE-2023-53728 in the wild and no public exploit code.

Sources

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

Also known as BELL-CVE-2023-53728, DEBIAN-CVE-2023-53728, GHSA-2cvf-73cf-jrw5, UBUNTU-CVE-2023-53728.