Vulnerability · Published May 26, 2026 · Assigned by GitHub_M
CVE-2026-48126Algernon: Host header path traversal in --domain mode reads files and runs Lua from parent dir
High 8.2
In plain English
A high-severity path traversal in algernon from xyproto. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 27% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Go | github.com/xyproto/algernon | 1.17.8 | GHSA-jc3j-x6pg-4hmv |
| Go | github.com/xyproto/algernon | 1.17.8 | GO-2026-5460 |
Affected products (as reported)
Weakness: CWE-22, CWE-23, CWE-644 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N
References
- https://github.com/xyproto/algernon/security/advisories/GHSA-jc3j-x6pg-4hmv x_refsource_CONFIRM