CVE-2026-48126
Algernon: Host header path traversal in --domain mode reads files and runs Lua from parent dir
- Published
- Updated
- Reserved
- Assigned by
- GitHub_M
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.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_MCNA (assigner) | 3.1 | High8.2 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N |
| NVDNVD · Deferred | 3.1 | High8.2 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N |
- EPSS (exploitation in 30 days)
- 0.34% · top 73% of all CVEs (6 Nov 2026)
- CISA SSVC
- Exploitation: poc · Automatable: yes · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: High 8.2.
Weakness
- CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') (opens in a new tab)All about CWE-22 and its CVEs
- CWE-23: Relative Path Traversal (opens in a new tab)All about CWE-23 and its CVEs
- CWE-644: Improper Neutralization of HTTP Headers for Scripting Syntax (opens in a new tab)All about CWE-644 and its CVEs
Affected products
Affected packages
From reviewed advisories of the GitHub Advisory Database.
- Gogithub.com/xyproto/algernonGHSA-jc3j-x6pg-4hmv (opens in a new tab)
References (1)
- https://github.com/xyproto/algernon/security/advisories/GHSA-jc3j-x6pg-4hmv (opens in a new tab)x_refsource_CONFIRMexploit
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisory GHSA-jc3j-x6pg-4hmv (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://trackcve.app/cve/CVE-2026-48126)Record last updated .