What’s Vulnerable › Vulnerabilities

CVE-2026-67191: Xlight FTP Server < 3.9.5 Pre-Auth Heap Buffer Overflow via SSH Parser

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.0% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-29 · updated 2026-10-23
• Weakness: CWE-122

Description

Xlight FTP Server before 3.9.5 contains a pre-authentication heap buffer overflow vulnerability that allows remote unauthenticated attackers to write past the end of a heap buffer by sending a malformed SSH client identification string. A logic error in the recv loop's termination condition uses an incorrect OR operator where an AND operator is required, enabling exploitation on any SSH or SFTP connection before authentication occurs.

Affected products

• Xlight FTP Server: before 3.9.5 — fixed in 3.9.5

How to fix

Upgrade to a fixed version: Xlight FTP Server 3.9.5. Check the vendor advisory for mitigations.

References

• https://www.vulncheck.com/advisories/xlight-ftp-server-pre-auth-heap-buffer-overflow-via-ssh-parser
• https://www.xlightftpd.com/whatsnew.htm

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