Vulnerability · Published Jul 29, 2026 · Assigned by VulnCheck

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

Critical 9.8

In plain English

A critical-severity heap buffer overflow in Xlight FTP Server from Xlight. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 1.0% (higher than 62% of all known vulnerabilities).

Severity (CVSS 3.1)9.8Critical

Exploit odds (30 days)1.0%top 38.2% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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 (as reported)

Vendor	Product	Versions
Xlight	Xlight FTP Server	0 – before 3.9.5

Weakness: CWE-122 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

References

Changelog release-notes
https://www.vulncheck.com/advisories/xlight-ftp-server-pre-auth-heap-buffer-overflow-via-ssh-parser third-party-advisory