CVE-2026-67191Xlight Xlight FTP Server Heap-based Buffer Overflow
NVD
Vulnerability Summary
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 v4.0 Base Metrics — Score 9.3 (CRITICAL)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:NAttack VectorNetwork
Attack ComplexityLow
Attack RequirementsNone
Privileges RequiredNone
User InteractionNone
Confidentiality (Vulnerable System)High
Integrity (Vulnerable System)High
Availability (Vulnerable System)High
Confidentiality (Subsequent System)None
Integrity (Subsequent System)None
Availability (Subsequent System)None
Show CVSS v3.x metrics (score 9.8)
CVSS v3.1 Base Metrics — Score 9.8 (CRITICAL)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HAttack VectorNetwork
Attack ComplexityLow
Privileges RequiredNone
User InteractionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
Affected & Patched Versions
- Xlight Xlight FTP Server < 3.9.5
- Xlight Xlight FTP Server 3.9.5
What to do
Plan remediation soon. No exploitation is confirmed yet, but the severity is critical.
- Check whether you run Xlight Xlight FTP Server and which version.
- Update to a patched version listed above, then confirm the new version.
Timeline
- Jul 29, 2026Published
- Jul 29, 2026Record last modified
Score, severity and exploitation changes are tracked from the day Watchtower started logging them.
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Data last checked: Nov 14, 2026 13:06 UTC