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Medium, CVSS 6.5amended

Backstage catalog rules can be bypassed for URL locations using encoded path segments

CVE-2026-115923GHSA-w658-mh9p-ww8f

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (@backstage/plugin-catalog-backend 4.0.2, 3.9.2), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
6.5 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
EPSS
  • CVE-2026-115923: 0.32% estimated exploitation activity in the next 30 days; percentile 24.74 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary `@backstage/plugin-catalog-backend` matches URL-type locations against `catalog.rules` location patterns using the raw URL string submitted by the user, while URL readers resolve that same string in canonical form when fetching the location's content. A URL can therefore be crafted so that it appears to belong to a trusted location scope during rule evaluation, but is fetched from a different scope.

Details When a deployment restricts catalog kinds to trusted URL prefixes using `catalog.rules` location patterns, `DefaultCatalogRulesEnforcer` applies glob matching directly to the raw `location.target` string. The URL readers used for ingestion resolve the same target in canonical form, including normalizing percent-encoded dot segments. A registered location such as `https:// /trusted/%2e%2e/attacker/repo/blob/main/catalog-info.yaml` matches a `https:// /trusted/**` pattern as a raw string, but resolves to and is fetched from `https:// /attacker/repo/...` when its…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from osv record GHSA-w658-mh9p-ww8f

  2. Revision 1 · created ·

    Published from ghsa record GHSA-w658-mh9p-ww8f

Agent brief

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# Patch Next advisory brief: CVE-2026-115923

Advisory: Backstage catalog rules can be bypassed for URL locations using encoded path segments
IDs: CVE-2026-115923, GHSA-w658-mh9p-ww8f
Record: https://patchnext.com/advisories/cve-2026-115923 (revision 2, source checked 29 Oct 2026, 06:00 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @backstage/plugin-catalog-backend 4.0.2, 3.9.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @backstage/plugin-catalog-backend: affected < 3.9.2; >= 4.0.0, < 4.0.2; fixed in 3.9.2, 4.0.2

## Suggested inspection (read-only)
- `npm ls @backstage/plugin-catalog-backend --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @backstage/plugin-catalog-backend.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-w658-mh9p-ww8f (GitHub-reviewed advisory GHSA-w658-mh9p-ww8f lists affected ranges: npm @backstage/plugin-catalog-backend >=0 =4.0.0 <4.0.2)
- Verified: https://osv.dev/vulnerability/GHSA-w658-mh9p-ww8f (OSV record GHSA-w658-mh9p-ww8f lists affected ranges: npm @backstage/plugin-catalog-backend >=0 =4.0.0 <4.0.2 (fixed))

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