CVE-2026-48126

Summary

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.

Affected Software

Weaknesses

• CWE-22: CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
• CWE-23: CWE-23: Relative Path Traversal
• CWE-644: CWE-644: Improper Neutralization of HTTP Headers for Scripting Syntax

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: poc
  • Automatable: yes
  • Technical Impact: partial

Additional References

• https://github.com/xyproto/algernon/security/advisories/GHSA-jc3j-x6pg-4hmv

References

• https://github.com/xyproto/algernon/security/advisories/GHSA-jc3j-x6pg-4hmv

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