Remote Code Execution Vulnerability in Algernon Web Server by XYProto
CVE-2026-45721

9CRITICAL

Key Information:

Vendor

Xyproto

Status
Algernon
Vendor
CVE Published:
26 May 2026

What is CVE-2026-45721?

Algernon, a lightweight Go web server, contains a vulnerability that allows a remote attacker to gain unauthorized access to the server's execution environment. Prior to version 1.17.7, when a request is made to a URL path that leads to a directory without an index file, the server performs a directory traversal. This traversal can lead the server to search for an attacker-supplied file named handler.lua, excessively traversing up until it reaches the filesystem root. If the file is found, it is executed with full server API access, allowing for pre-authenticated remote code execution. This risk exists without authentication checks as the handler-resolution step occurs before permission validation. The vulnerability has been resolved in version 1.17.7.

Affected Version(s)

algernon < 1.17.7

References

https://github.com/xyproto/algernon/security/advisories/G...
x_refsource_CONFIRM

CVSS V3.1

Score:
9
Severity:
CRITICAL
Confidentiality:
High
Integrity:
High
Availability:
High
Attack Vector:
Network
Attack Complexity:
High
Privileges Required:
None
User Interaction:
None
Scope:
Changed

Timeline

  • Vulnerability published

  • Vulnerability Reserved

.