# Backstage: Improper validation of TechDocs MkDocs configuration

Advisory record · `GHSA-qmw3-745m-w99g`

- **Identifiers:** `GHSA-qmw3-745m-w99g` · `CVE-2026-106558`
- **State:** Confirmed
- **Severity:** CVSS 8.8 High
- **Critical:** No
- **Weakness (CWE):** [CWE-502](https://cwe.mitre.org/data/definitions/502.html)
- **Tags:** [Insecure deserialization](https://agentprime.io/advisories/tag/deserialization.md)
- **Published:** 7 Oct 2026
- **Updated:** 7 Oct 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 7 Oct 2026, 18:03 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `@backstage/plugin-techdocs-node` (npm): affected `<1.15.4`; fixed in `1.15.4`

## 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

- 8.8 High, CVSS 3.1: `CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0047, the 40th percentile, on 7 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 13:33 UTC: First seen by agentprime
- 31 Oct 2026, 13:33 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-qmw3-745m-w99g)

## Sources

- [GitHub Advisory Database: GHSA-qmw3-745m-w99g](https://github.com/advisories/GHSA-qmw3-745m-w99g)
- [OSV: GHSA-qmw3-745m-w99g](https://osv.dev/vulnerability/GHSA-qmw3-745m-w99g)
- <https://github.com/backstage/backstage/security/advisories/GHSA-qmw3-745m-w99g>
- <https://nvd.nist.gov/vuln/detail/CVE-2026-106558>
- <https://github.com/backstage/backstage/commit/32723a0fe4e12ed80535fc65d5331765c55aa91b>
- <https://github.com/backstage/backstage/commit/944edb51c8524d3664b18f2d57ba101b1c93b709>
- <https://github.com/backstage/backstage/commit/f18e9abcc6051491862b15e4fc60e69f8d52310c>
- <https://github.com/backstage/backstage>
- <https://github.com/backstage/backstage/releases/tag/v1.50.7>
- <https://github.com/backstage/backstage/releases/tag/v1.54.9>
- <https://github.com/backstage/backstage/releases/tag/v1.55.2>

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-qmw3-745m-w99g>, 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-qmw3-745m-w99g/>. Everything for agents: <https://agentprime.io/llms.txt>.