# Critical security issues in XML encoding in github.com/dexidp/dex

Advisory record · `GHSA-m9hp-7r99-94h5`

- **Identifiers:** `GHSA-m9hp-7r99-94h5` · `CVE-2020-26290` · `CVE-2020-27847` · `GHSA-2x32-jm95-2cpx`
- **State:** Confirmed
- **Severity:** CVSS 9.3 Critical
- **Critical:** Yes: CVSS 9+
- **Weakness (CWE):** [CWE-228](https://cwe.mitre.org/data/definitions/228.html) · [CWE-347](https://cwe.mitre.org/data/definitions/347.html)
- **Tags:** [Weak cryptography or TLS](https://agentprime.io/advisories/tag/weak-crypto.md) · [CWE-228](https://agentprime.io/advisories/tag/cwe-228.md)
- **Published:** 20 Dec 2021
- **Updated:** 10 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 20 Dec 2021, 17:53 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Critical

Critical, because:

- CVSS score 9.3: 9.0 or more.

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

## Affected packages

- `github.com/dexidp/dex` (Go): affected `<2.27.0`; fixed in `2.27.0`
- `github.com/russellhaering/goxmldsig` (Go): affected `<1.1.0`; fixed in `1.1.0`

## 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

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

- **CISA KEV:** Not listed.
- **EPSS:** 0.017, the 77th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:45 UTC: First seen by agentprime
- 31 Oct 2026, 14:45 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-m9hp-7r99-94h5)

## Sources

- [GitHub Advisory Database: GHSA-m9hp-7r99-94h5](https://github.com/advisories/GHSA-m9hp-7r99-94h5)
- [OSV: GHSA-m9hp-7r99-94h5](https://osv.dev/vulnerability/GHSA-m9hp-7r99-94h5)
- <https://github.com/dexidp/dex/security/advisories/GHSA-m9hp-7r99-94h5>
- <https://github.com/russellhaering/goxmldsig/security/advisories/GHSA-q547-gmf8-8jr7>
- <https://nvd.nist.gov/vuln/detail/CVE-2020-26290>
- <https://github.com/dexidp/dex/commit/324b1c886b407594196113a3dbddebe38eecd4e8>
- <https://github.com/russellhaering/goxmldsig/commit/f6188febf0c29d7ffe26a0436212b19cb9615e64>
- <https://github.com/dexidp/dex/releases/tag/v2.27.0>
- <https://github.com/mattermost/xml-roundtrip-validator/blob/master/advisories/unstable-attributes.md>
- <https://github.com/mattermost/xml-roundtrip-validator/blob/master/advisories/unstable-directives.md>
- <https://github.com/mattermost/xml-roundtrip-validator/blob/master/advisories/unstable-elements.md>
- <https://mattermost.com/blog/coordinated-disclosure-go-xml-vulnerabilities>
- <https://pkg.go.dev/vuln/GO-2020-0050>

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-m9hp-7r99-94h5>, 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-m9hp-7r99-94h5/>. Everything for agents: <https://agentprime.io/llms.txt>.