CVE-2026-67191

Deferred Deferred - Pending Action

Heap Buffer Overflow in Xlight FTP Server

Publication date: 2026-07-29

Last updated on: 2026-07-29

Assigner: VulnCheck

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.

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-07-29

Last Modified

2026-07-29

Generated

2026-08-19

AI Q&A

2026-07-30

EPSS Evaluated

2026-08-18

NVD

CVE-2026-67191

Affected Vendors & Products

Vendor	Product	Version / Range
xlight	ftp_server	to 3.9.5 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-122	A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().

Attack-Flow Graph

Executive Summary

Xlight FTP Server before version 3.9.5 has a pre-authentication heap buffer overflow flaw. Attackers can exploit this by sending a malformed SSH client identification string, causing the server to write past the end of a heap buffer. The issue stems from a logic error in the receive loop's termination condition, where an incorrect OR operator is used instead of an AND operator.

Detection Guidance

Detecting this vulnerability requires monitoring for malformed SSH client identification strings or unusual heap buffer overflow patterns. Use network traffic analysis tools like Wireshark to inspect SSH/SFTP connections for irregular payloads. Check Xlight FTP Server logs for crashes or memory corruption errors during authentication attempts.

Impact Analysis

This vulnerability allows remote unauthenticated attackers to execute arbitrary code on the server with high privileges. It can lead to complete system compromise, data theft, or denial of service. Since exploitation occurs before authentication, any exposed Xlight FTP Server instance is at risk.

Compliance Impact

This vulnerability could lead to unauthorized access to sensitive data, violating GDPR and HIPAA requirements for data protection and confidentiality. Organizations using vulnerable versions may face compliance violations, legal penalties, and reputational damage due to potential data breaches.

Mitigation Strategies

Immediately update Xlight FTP Server to version 3.9.5 or later. If an update is not possible, restrict network access to the FTP server using firewalls or disable SSH/SFTP services until patched. Monitor for exploitation attempts and isolate affected systems if compromised.

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