xyproto algernon up to 1.17.7 engine/flags.go path traversal

Summaryinfo

A vulnerability was found in xyproto algernon up to 1.17.7 and classified as critical. The affected element is an unknown function of the file engine/flags.go. The manipulation results in path traversal. This vulnerability is reported as CVE-2026-48126. The attack can be launched remotely. No exploit exists. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability was found in xyproto algernon up to 1.17.7. It has been classified as critical. Affected is an unknown code of the file engine/flags.go. The manipulation with an unknown input leads to a path traversal vulnerability. CWE is classifying the issue as CWE-22. The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

Algernon is a small self-contained pure-Go web server. Prior to 1.17.8, when algernon is started with --domain (or --letsencrypt, which silently turns on --domain at engine/flags.go:372), the request handler resolves the served directory by joining the configured --dir with the value of the client-supplied Host header. The join is performed by filepath.Join with no validation, so a Host: .. header walks one level above the document root. Subsequent file resolution then exposes everything in that parent directory — arbitrary file read, full directory listing, and, if any .lua file is present, server-side Lua execution. This vulnerability is fixed in 1.17.8.

The advisory is shared for download at github.com. This vulnerability is traded as CVE-2026-48126 since 05/20/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1006.

Upgrading to version 1.17.8 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-31881). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Productinfo

Vendor

• xyproto

Name

• algernon

Version

• 1.17.0
• 1.17.1
• 1.17.2
• 1.17.3
• 1.17.4
• 1.17.5
• 1.17.6
• 1.17.7

Website

• Product: https://github.com/xyproto/algernon/

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VulDB is the best source for vulnerability data and more expert information about this specific topic.

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