CVE-2026-99203

pipe: preserve existing fasync readers on writer setup failure

Published Oct 28, 2026 CVSS 3.1 · 7.8 High EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Debian DLA Debian DLA DLA-4904-1 linux-6.12 security update
History
Type Values Removed Values Added
Metrics cvssV3_1

{'score': 4.7, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H'}

cvssV3_1

{'score': 7.8, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'}

Type Values Removed Values Added
Weaknesses CWE-416
Type Values Removed Values Added
Weaknesses CWE-825
References
Metrics threat_severity

None

cvssV3_1

{'score': 4.7, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H'}

threat_severity

Moderate

Type Values Removed Values Added
First Time appeared Linux linux
Vendors & Products Linux linux
Type Values Removed Values Added
Weaknesses CWE-416
Type Values Removed Values Added
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.
Title pipe: preserve existing fasync readers on writer setup failure
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References
Weaknesses

Sources

Status
PUBLISHED
Assigner
Linux
Published
Updated
Oct 31, 2026, 12:45 PM
Reserved
Sep 25, 2026, 10:25 AM
Status
Received
Published
Oct 28, 2026, 11:17 AM
Modified
Oct 31, 2026, 1:17 PM
Severity
Moderate
Public date
Oct 28, 2026, 12:00 AM