VulnerabilityPublished 28 Oct 2026

CVE-2026-99203: Linux kernel · pipe: preserve existing fasync readers on writer setup failure

Affects Linux kernelSource CVE Database V5

Not known to be exploited · fixed in 2259809e5b7043c4ba20af7b14ba3e471cf55521 : update Linux kernel when convenient.

Data as of 28 Oct 2026, 10:58 UTC

Severity

Unrated

Rated by Threat Radar · CVSS not yet scored by NVD

Patch: Available – fixed in 2259809e5b7043c4ba20af7b14ba3e471cf55521, 40bb03d3ea6f6a915218508819ecc4d7a7fa260d, 4c42ce499ce4b1c787e61082e3b13df4f30c4eaa

Exploitation evidence

Disclosed: evidence found.
CVE published 28 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade Linux kernel to 2259809e5b7043c4ba20af7b14ba3e471cf55521, 40bb03d3ea6f6a915218508819ecc4d7a7fa260d or 4c42ce499ce4b1c787e61082e3b13df4f30c4eaa.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ 76398425bb06b07cc3a3b1ce169c67dc9d6874ed, < 2259809e5b7043c4ba20af7b14ba3e471cf55521	Fixed in 2259809e5b7043c4ba20af7b14ba3e471cf55521
LinuxLinux	Affected ≥ 76398425bb06b07cc3a3b1ce169c67dc9d6874ed, < 40bb03d3ea6f6a915218508819ecc4d7a7fa260d	Fixed in 40bb03d3ea6f6a915218508819ecc4d7a7fa260d
LinuxLinux	Affected ≥ 76398425bb06b07cc3a3b1ce169c67dc9d6874ed, < 4c42ce499ce4b1c787e61082e3b13df4f30c4eaa	Fixed in 4c42ce499ce4b1c787e61082e3b13df4f30c4eaa
LinuxLinux	Affected =2.6.30	Fixed in–

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.

References

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