Pre-authentication heap corruption via SSH identification parsing
Published Jul 29, 2026 · Updated Jul 29, 2026
Heap buffer overflow in Xlight FTP Server before 3.9.5 allows remote attackers to corrupt heap memory via a malformed SSH identification string. The SSH receive loop uses OR instead of AND in its termination test, so an overlong client identification writes beyond the allocated heap buffer. Any SSH or SFTP connection reaches this parser before authentication, allowing memory corruption without credentials or user interaction.
Summary
What happened
Heap buffer overflow in Xlight FTP Server before 3.9.5 allows remote attackers to corrupt heap memory via a malformed SSH identification string. The SSH receive loop uses OR instead of AND in its termination test, so an overlong client identification writes beyond the allocated heap buffer. Any SSH or SFTP connection reaches this parser before authentication, allowing memory corruption without credentials or user interaction.
The record
- CVE
- CVE-2026-67191
- Published
- Jul 29, 2026
- Updated
- Jul 29, 2026
- Vendor
- Xlight
- Product
- Xlight FTP Server
- Classifications
- CWE-122, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jul 29, 2026CVE publishedPublication date reported by the CVE source.
- Jul 29, 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 <3.9.5
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.
Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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