---
id: "CVE-2026-115923"
kind: "vulnerability"
aliases: ["CVE-2026-115923"]
title: "Backstage catalog: encoded URLs bypass location rules, admitting untrusted entities"
severity: "medium"
cvss: 6.5
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["backstage", "developer-portal", "package", "self-hosted"]
not_affected_if: ["auth-required", "default-config"]
published_at: "2026-10-26T18:17:40+00:00"
first_seen_at: "2026-10-26T18:31:43+00:00"
updated_at: "2026-10-26T18:33:59+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-115923", "first_seen_at": "2026-10-26T18:31:43+00:00"}]
---

# Backstage catalog: encoded URLs bypass location rules, admitting untrusted entities

Backstage's catalog rules check the raw location URL, but the URL reader fetches a canonicalized version, so percent-encoded paths can make an untrusted source match a trusted pattern. An authenticated user who can create catalog locations can get untrusted entity content admitted as trusted.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the installed `@backstage/plugin-catalog-backend` version with `yarn why @backstage/plugin-catalog-backend` or `npm ls @backstage/plugin-catalog-backend`; versions below `3.9.2`, or from `4.0.0` through `4.0.1`, are affected.
- Review `catalog.rules` and `catalog.locations` in the app config for allow-listed URL patterns that users can add locations under.

## Fix

- Upgrade `@backstage/plugin-catalog-backend` to `3.9.2` on the 3.x line, or to `4.0.2` on the 4.x line.

## Timeline

- 2026-10-26T18:31:43+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-115923

## From the sources

Backstage is an open framework for building developer portals. Prior to 3.9.2 and from 4.0.0 until 4.0.2, DefaultCatalogRulesEnforcer in @backstage/plugin-catalog-backend compares the raw location.target URL against catalog.rules, while URL readers canonicalize the same URL before fetching it. An authenticated user with catalog.location.create permission can use percent-encoded path segments to make an untrusted URL match a trusted location pattern even though the canonical URL resolves outside that scope. This admits entity content from an untrusted source as trusted, while further downstream consequences depend on deployment configuration. This issue is fixed in versions 3.9.2 and 4.0.2.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_