NFSD: check truncate permission under inode lock
CVE-2026-89713 · published 11 Sept 2026
How serious is it
- Severity: critical, CVSS score 9.1 out of 10.
- No exploit prediction (EPSS) score yet.
- Not on the CISA list of exploited vulnerabilities.
- No public exploit in Exploit-DB.
Is your app affected by CVE-2026-89713?
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Who is affected
- Linux Linux: 783112f7401ff449d979530209b3f6c2594fdb4e to < 52d0c5bdfe232c9974d4b11f97078b9c7814f05d, 783112f7401ff449d979530209b3f6c2594fdb4e to < 3afa17d93ba8c925f49370c816c6dae5112d8c24, 783112f7401ff449d979530209b3f6c2594fdb4e to < d8352da196349182e1afd5a93308256cddc0a97d, 783112f7401ff449d979530209b3f6c2594fdb4e to < 44086254479035de42ca3d286ecf25521d4e6325
- Linux Linux: 4.11
How to check
- Find out whether you run the affected product and which version, then compare it with the versions above.
How to fix
Copies a prompt for Claude Code, Cursor or Codex that asks it to check whether you run this product.
- Apply the vendor's update or mitigation from the references below. If there is none yet, limit exposure of the affected service until there is.
- If a vulnerable version was live, check your logs and rotate the secrets that server could read.
The advisory
In the Linux kernel, the following vulnerability has been resolved:
NFSD: check truncate permission under inode lock
nfsd_setattr() checks whether a size update needs NFSD_MAY_TRUNC
before it takes inode_lock(). The comparison uses the file size sampled
by that unlocked read, but the actual ATTR_SIZE update is applied later
under inode_lock() by notify_change().
This leaves a TOCTOU window for append-only files. If a client sends a
SETATTR that does not shrink the file at the time of the unlocked
sample, a concurrent append can extend the file before nfsd_setattr()
takes inode_lock(). notify_change() then applies a real truncation
without the NFSD_MAY_TRUNC check that rejects IS_APPEND(inode). The VFS
truncate syscall paths perform their own append-only checks before
calling notify_change(), so NFSD must make this decision against the
locked size it is about to change.
Split the write-count acquisition from the truncation permission check.
Keep get_write_access() before the locked setattr work, then recheck
whether the requested size is below i_size_read(inode) after inode_lock()
has been acquired and before notify_change(ATTR_SIZE). This also avoids
the plain unlocked inode->i_size load.
Check your whole app
Dependencies are only half of it. Free and read-only: before you push, run npx shippable-dev scan localhost:3000 in your project folder, no account needed. For your live app, you prove it's yours with a one-line tag first.
References
- git.kernel.org/stable/c/52d0c5bdfe232c9974d4b11f97078b9c7814f05d
- git.kernel.org/stable/c/3afa17d93ba8c925f49370c816c6dae5112d8c24
- git.kernel.org/stable/c/d8352da196349182e1afd5a93308256cddc0a97d
- git.kernel.org/stable/c/44086254479035de42ca3d286ecf25521d4e6325
- git.kernel.org/stable/c/b778e0e0a16759f22a70579c3cf8d254a40d4a7f
Merged from CVE List. Last updated 26 Oct 2026. All vulnerabilities · RSS · JSON