Arbitrary file write via symlinked build cache
Published Jul 13, 2026 · Updated Jul 13, 2026
Symlink following in FlashAttention through 2.8.3.post1 allows local users to write files with victim privileges during source builds. hopper/setup.py's download_and_copy() passes a predictable cache path to tarfile.extractall() without rejecting a pre-planted symlink or filtering archive members. Exploitation requires write access to the victim's cache before a Hopper build downloads NVIDIA toolchains; the write occurs with the builder's privileges.
Summary
What happened
Symlink following in FlashAttention through 2.8.3.post1 allows local users to write files with victim privileges during source builds. hopper/setup.py's download_and_copy() passes a predictable cache path to tarfile.extractall() without rejecting a pre-planted symlink or filtering archive members. Exploitation requires write access to the victim's cache before a Hopper build downloads NVIDIA toolchains; the write occurs with the builder's privileges.
The record
- CVE
- CVE-2026-62239
- Published
- Jul 13, 2026
- Updated
- Jul 13, 2026
- Vendor
- Dao AI Lab
- Product
- FlashAttention
- Classifications
- CWE-59, T1068
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- Jul 13, 2026CVE publishedPublication date reported by the CVE source.
- Jul 13, 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=0 <=2.8.3.post1
What conditions does exploitation require?
What is affected?
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
Public exploit references
- Issue #2637 symlink proof of conceptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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