Linux Kernel: Pipe fasync Use-After-Free via F_SETFL/FIOASYNC
CVE-2026-99203 Published on October 28, 2026
pipe: preserve existing fasync readers on writer setup failure
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.
Products Associated with CVE-2026-99203
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Affected Versions
Linux:- Version 76398425bb06b07cc3a3b1ce169c67dc9d6874ed and below 4c42ce499ce4b1c787e61082e3b13df4f30c4eaa is affected.
- Version 76398425bb06b07cc3a3b1ce169c67dc9d6874ed and below 2259809e5b7043c4ba20af7b14ba3e471cf55521 is affected.
- Version 76398425bb06b07cc3a3b1ce169c67dc9d6874ed and below 40bb03d3ea6f6a915218508819ecc4d7a7fa260d is affected.
- Version 2.6.30 is affected.
- Before 2.6.30 is unaffected.
- Version 6.18.59, <= 6.18.* is unaffected.
- Version 7.2.13, <= 7.2.* is unaffected.
- Version 7.3, <= * is unaffected.