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Vulnerability record · CVE-2026-67191 · published 29 July 2026

CVE-2026-67191: Heap-based buffer overflow vulnerability

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.

9.3 CVSS 4.0 Critical EPSS 0.96% · top 39.9% CWE-122 · Heap-based buffer overflow Deferred
9.3CVSS 4.0 base score
0.96%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
2References
30 Jul 2026Last modified by NVD

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:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

References

LinkTags
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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Source: NIST National Vulnerability Database (record CVE-2026-67191), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.