CVE-2026-99203 pipe: preserve existing fasync readers on writer setup failure
- Exploited in the wild
- Not known
- Fix
- Available
What is CVE-2026-99203?
CVE-2026-99203 is a vulnerability in Linux, published on 28 Oct 2026.
Official description
In the Linux kernel, the following vulnerability has been resolved:
pipe: preserve existing fasync readers on writer setup failure
F_SETFL and FIOASYNC decide whether to invoke ->fasync() before pipe_fasync() takes pipe->mutex. Two enables of one O_RDWR FIFO can therefore both enter the callback.
fasync_helper() allocates before checking for an existing entry. If the first enable installs both entries, a second enable can update the reader entry and then fail the allocation for the writer entry. The error path removes the pre-existing reader entry, clearing FASYNC while the writer entry remains registered. __fput() then skips ->fasync(), so a later pipe notification can dereference the freed file or its f_owner. An unprivileged memory-pressure reproducer triggers a KASAN slab-use-after-free in send_sigio() through this path.
Keep the reader helper's result and undo the registration only if this call added it. The pipe mutex serializes changes to both lists, so a failed new registration still removes its reader, while a failed duplicate preserves the existing registrations and FASYNC. Successful duplicate enables continue to update fa_fd as before.
Which versions are affected by CVE-2026-99203?
How do I fix CVE-2026-99203?
Upgrade to a fixed version.
Is CVE-2026-99203 being exploited?
There is no known exploitation of CVE-2026-99203 in the wild and no public exploit code.
Sources
Also known as AZL-111365, BELL-CVE-2026-99203, DEBIAN-CVE-2026-99203, GHSA-j875-7x9h-g92w, UBUNTU-CVE-2026-99203.