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

Quick assessment

Affected
Xlight Xlight FTP Server
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

xlight ftp server是xlight ftp server个人开发者的一款轻量级FTP服务器软件。 Xlight FTP Server 3.9.5之前版本存在缓冲区错误漏洞，该漏洞源于预认证堆缓冲区溢出，由于recv循环终止条件逻辑错误（使用了错误的OR运算符），导致远程未认证攻击者通过发送畸形SSH客户端标识字符串，可写入堆缓冲区之外。

CVSS 9.8 · Critical EPSS 0.96% · P61

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
Xlight Xlight FTP Server < 3.9.5 affected
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I. Basic Information for CVE-2026-67191

Vulnerability Information
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Vulnerability Title
Xlight FTP Server < 3.9.5 Pre-Auth Heap Buffer Overflow via SSH Parser
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
堆缓冲区溢出
Source: CVE Program / CVE List V5
Vulnerability Title
Xlight FTP Server 缓冲区错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
xlight ftp server是xlight ftp server个人开发者的一款轻量级FTP服务器软件。 Xlight FTP Server 3.9.5之前版本存在缓冲区错误漏洞，该漏洞源于预认证堆缓冲区溢出，由于recv循环终止条件逻辑错误（使用了错误的OR运算符），导致远程未认证攻击者通过发送畸形SSH客户端标识字符串，可写入堆缓冲区之外。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Xlight Xlight FTP Server 0 ~ 3.9.5 -

II. Public POCs for CVE-2026-67191

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III. Intelligence Information for CVE-2026-67191

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Vendor Pages for CVE-2026-67191 (1)

Other References for CVE-2026-67191 (1)

Same Patch Batch · Xlight · 2026-07-29 · 3 CVEs total

CVE-2026-67192 8.1 HIGH Xlight FTP Server < 3.9.5 Pre-Auth Stack Buffer Overflow via SSH GCM Cipher
CVE-2026-67193 5.3 MEDIUM Xlight FTP Server < 3.9.5 Information Disclosure via USER Command

IV. Related Vulnerabilities

Same product: Xlight FTP Server
Same vendor: Xlight
Same weakness: CWE-122

V. Comments for CVE-2026-67191

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