# Algernon: handler.lua discovery walks parent directories above the server root

Advisory record · `GHSA-xwcr-wm99-g9jc`

- **Identifiers:** `GHSA-xwcr-wm99-g9jc` · `CVE-2026-45721` · `GO-2026-5772`
- **State:** Confirmed
- **Severity:** CVSS 9.0 Critical
- **Critical:** Yes: CVSS 9+
- **Weakness (CWE):** [CWE-20](https://cwe.mitre.org/data/definitions/20.html) · [CWE-426](https://cwe.mitre.org/data/definitions/426.html) · [CWE-552](https://cwe.mitre.org/data/definitions/552.html)
- **Tags:** [Information disclosure](https://agentprime.io/advisories/tag/info-disclosure.md) · [CWE-20](https://agentprime.io/advisories/tag/cwe-20.md) · [CWE-426](https://agentprime.io/advisories/tag/cwe-426.md)
- **Published:** 19 May 2026
- **Updated:** 25 Jun 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 19 May 2026, 14:36 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Critical

Critical, because:

- CVSS score 9.0: 9.0 or more.

How we decide what’s critical: <https://agentprime.io/advisories/critical.md>

## Affected packages

- `github.com/xyproto/algernon` (Go): affected `<1.17.7`; fixed in `1.17.7`

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 9.0 Critical, CVSS 3.1: `CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0044, the 38th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 15:06 UTC: First seen by agentprime
- 31 Oct 2026, 15:06 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-xwcr-wm99-g9jc)

## Sources

- [GitHub Advisory Database: GHSA-xwcr-wm99-g9jc](https://github.com/advisories/GHSA-xwcr-wm99-g9jc)
- [OSV: GHSA-xwcr-wm99-g9jc](https://osv.dev/vulnerability/GHSA-xwcr-wm99-g9jc)
- <https://github.com/xyproto/algernon/security/advisories/GHSA-xwcr-wm99-g9jc>
- <https://github.com/xyproto/algernon>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-xwcr-wm99-g9jc>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-xwcr-wm99-g9jc/>. Everything for agents: <https://agentprime.io/llms.txt>.