io_uring/poll: avoid retry wakeup loss when dropping ownership
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- No known exploitation
- Fix
- Fixed in 5.16, 6.1
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 5.16, 6.1.
- Exploitation?/40Exploitation: unknown (data gap). No CISA SSVC exploitation rating yet
- Exposure?/25Exposure: unknown (data gap). No advisory context yet
- Reach20/20Affects Linux kernel (software on nearly every server, desktop or phone)
- Severity?/10Severity: unknown (data gap). No CVSS score or vendor rating
- No patch0/5No signal
What would change the score
- Would score about 75 if added to CISA KEV
- Would score about 70 if CISA's SSVC rates exploitation active
- Would score about 42 if advisories confirm default setups are exposed
CVE-2026-99263 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It affects Linux; fixed in 5.16 and 6.1.
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- Published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 20/100 · provisional
- Fix
- Fixed in 5.16, 6.1
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
The vulnerability affects the Linux kernel's io_uring asynchronous I/O subsystem, specifically its poll handling. Under certain timing conditions, a wakeup can be lost during retry processing, causing requests to stall until an unrelated event occurs.
Read the original description
In the Linux kernel, the following vulnerability has been resolved: io_uring/poll: avoid retry wakeup loss when dropping ownership If a wakeup sets IO_POLL_RETRY_FLAG between the owning task consuming the existing instance of IO_POLL_RETRY_FLAG and the loop check of io_poll_check_events(), then we stall on processing the request until an unrelated wakeup comes along. Using atomic_cmpxchg instead of atomic_sub_return to guarantee both the count v and poll_refs are 0 and no wake-ups are missed.
What to do
Upgrade to a fixed version: 5.16, 6.1.
Timeline
- CVE published
- First seen by cve.now
- Record last updated
Affected versions
- Linux Linux
From 5.15.82 · fixed in 5.16; From 6.0.11 · fixed in 6.1
- Linux Linux
6.1
Evidence 7
- Link
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Corrections
None so far.
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Questions about CVE-2026-99263
Is CVE-2026-99263 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
Which versions are affected by CVE-2026-99263?
Linux: from 5.15.82 before 5.16; from 6.0.11 before 6.1. Linux: version 6.1.Source: cve.now feed data
How do I fix CVE-2026-99263?
Upgrade to a fixed version: 5.16, 6.1.Source: cve.now feed data