Executive brief
Xlight FTP Server, a high-performance file transfer server, is vulnerable to a critical security flaw in its SSH and SFTP handling. An unauthenticated remote attacker can exploit this vulnerability to gain full control over the server or cause it to crash by sending a specially crafted identification string. This could lead to the theft of sensitive customer data, complete service disruption, and a significant impact on business operations.
Technical details
A heap-based buffer overflow vulnerability exists in Xlight FTP Server versions prior to 3.9.5 due to a logic error in the SSH client identification string parser. The root cause is an incorrect use of an OR operator instead of an AND operator in the receive loop's termination condition, which allows an attacker to write data past the end of a heap buffer. This vulnerability is reachable over the network without authentication via any SSH or SFTP connection. Successful exploitation can lead to arbitrary code execution or a server crash. The issue was addressed in version 3.9.5.
Affected products
- Xlight Xlight FTP Server before 3.9.5
Timeline
- 2026-07-01: patched: Version 3.9.5 released to address security vulnerabilities.
- 2026-07-29: disclosed: Vulnerability details published by VulnCheck and NVD.