Tmpfs data loss via dropped PMD dirty bit
Published Sep 16, 2026 · Updated Sep 16, 2026
Improper dirty-state handling in Linux 4.8 allows local users to cause silent data loss in shared tmpfs mappings during reclaim. zap_huge_pmd_folio() drops a file-backed PMD without copying its hardware dirty bit to the folio, so reclaim treats written shmem as clean and frees it without swap-out. Exposure requires a read-faulted PMD-sized MAP_SHARED tmpfs folio, shmem THP, swap, an unmap, and later reclaim; affected contents return as zeroes.
Summary
What happened
Improper dirty-state handling in Linux 4.8 allows local users to cause silent data loss in shared tmpfs mappings during reclaim. zap_huge_pmd_folio() drops a file-backed PMD without copying its hardware dirty bit to the folio, so reclaim treats written shmem as clean and frees it without swap-out. Exposure requires a read-faulted PMD-sized MAP_SHARED tmpfs folio, shmem THP, swap, an unmap, and later reclaim; affected contents return as zeroes.
The record
- CVE
- CVE-2026-89987
- Published
- Sep 16, 2026
- Updated
- Sep 16, 2026
- Vendor
- The Linux Kernel Organization
- Product
- Linux
- Classifications
- Unavailable
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- Sep 16, 2026CVE publishedPublication date reported by the CVE source.
- Sep 16, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
Compare your product and version with the public record. A matching version still requires validation against your environment.
Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=4.8
- Affected versionversion=b5072380eb619786990cd9eab3ade05d09ccd89e <9435cddf1378d149d826bd7bd1448a44bf96868d
- Affected versionversion=b5072380eb619786990cd9eab3ade05d09ccd89e <effe3cc6d4fdd407457eb30f7b0ef094393f0d64
- Affected versionversion=b5072380eb619786990cd9eab3ade05d09ccd89e <fe6cf984939d8e12cb33a99673c8d026c5135e68
What conditions does exploitation require?
What is affected?
Published CVSS scores
No CVSS assessment is available in this record.
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
No sourced classifications are available.
Public exploit references
No public exploit references are available in this record.
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
Check the software in your environment
Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.
Book a demo