Unauthorized truncation via unlocked NFSD size check
Published Sep 11, 2026 · Updated Sep 11, 2026
TOCTOU in Linux NFSD allows remote authenticated users to truncate append-only files through concurrent NFS SETATTR and append operations. nfsd_setattr checks the requested size against an unlocked inode size, then notify_change applies ATTR_SIZE after a concurrent append without repeating NFSD_MAY_TRUNC under inode_lock. Exploitation requires write-authorized NFS access to an append-only file and successful race timing; the bounded consequence is unauthorized loss of appended file data.
Summary
What happened
TOCTOU in Linux NFSD allows remote authenticated users to truncate append-only files through concurrent NFS SETATTR and append operations. nfsd_setattr checks the requested size against an unlocked inode size, then notify_change applies ATTR_SIZE after a concurrent append without repeating NFSD_MAY_TRUNC under inode_lock. Exploitation requires write-authorized NFS access to an append-only file and successful race timing; the bounded consequence is unauthorized loss of appended file data.
The record
- CVE
- CVE-2026-89713
- Published
- Sep 11, 2026
- Updated
- Sep 11, 2026
- Vendor
- The Linux Kernel Organization
- Product
- Linux
- Classifications
- T1565.001
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Sep 11, 2026CVE publishedPublication date reported by the CVE source.
- Sep 11, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=3.16.44 <3.17
- Affected versionversion=3.2.89 <3.3
- Affected versionversion=3ee4f442e5b37a537297b812557b1163f96b5399
- Affected versionversion=4.10.2 <4.11
- Affected versionversion=4.11
- Affected versionversion=4.4.53 <4.5
- Affected versionversion=4.9.14 <4.10
- Affected versionversion=604a3c407026d6162d15300478e63f901e435efc
- Affected versionversion=783112f7401ff449d979530209b3f6c2594fdb4e <3afa17d93ba8c925f49370c816c6dae5112d8c24
- Affected versionversion=783112f7401ff449d979530209b3f6c2594fdb4e <44086254479035de42ca3d286ecf25521d4e6325
- Affected versionversion=783112f7401ff449d979530209b3f6c2594fdb4e <b778e0e0a16759f22a70579c3cf8d254a40d4a7f
- Affected versionversion=783112f7401ff449d979530209b3f6c2594fdb4e <d8352da196349182e1afd5a93308256cddc0a97d
- Affected versionversion=982898d7f97a35447403c3fcecc0d96c646ce101
- Affected versionversion=a3c6cbc4eac4473ed5461d5faae2794d3e5c0e44
- Affected versionversion=cc4d5dc73841b98d33cdfb9822d70b0aac4beca5
What conditions does exploitation require?
What is affected?
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Attacks
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Technologies
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