# CVE-2026-115923: Backstage catalog rules can be bypassed for URL locations using encoded path segments

Status: published. Published: 2026-10-26. Updated: 2026-11-02.

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.

## Remediation

- fix: @backstage/plugin-catalog-backend (npm): OSV reports a fixed version 3.9.2. Check the advisory for supported release branches. (source: OSV GHSA-w658-mh9p-ww8f) — https://github.com/advisories/GHSA-w658-mh9p-ww8f
- fix: @backstage/plugin-catalog-backend (npm): OSV reports a fixed version 4.0.2. Check the advisory for supported release branches. (source: OSV GHSA-w658-mh9p-ww8f) — https://github.com/advisories/GHSA-w658-mh9p-ww8f

## Affected products and versions

- backstage / backstage: < 3.9.2 (affected); >= 4.0.0, < 4.0.2 (affected). Source: CNA: GitHub_M
-  / @backstage/plugin-catalog-backend (@backstage/plugin-catalog-backend): ≥ 0; < 3.9.2 (affected, semver); OSV events: introduced 0; fixed 3.9.2. Source: OSV GHSA-w658-mh9p-ww8f
-  / @backstage/plugin-catalog-backend (@backstage/plugin-catalog-backend): ≥ 4.0.0; < 4.0.2 (affected, semver); OSV events: introduced 4.0.0; fixed 4.0.2. Source: OSV GHSA-w658-mh9p-ww8f

## Severity and prioritization

- CVSS 3.1: 6.5 (medium); CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N; source: CNA: GitHub_M

- CISA KEV: No listing in collected sources

- EPSS: 0.32% as of 2026-11-02; percentile 24.70%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-22

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/backstage/backstage/security/advisories/GHSA-w658-mh9p-ww8f (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/backstage/backstage/commit/3214dc8f15d4a08a2fd07a72a8fe4d00aeac0db4 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/backstage/backstage/commit/737ff1c719dbd5a97f375b7f1db6d61416618419 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/backstage/backstage/releases/tag/v1.54.10 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/backstage/backstage/releases/tag/v1.56.1 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/advisories/GHSA-w658-mh9p-ww8f (OSV / GitHub Security Advisories; advisory)

- https://osv.dev/vulnerability/GHSA-w658-mh9p-ww8f (OSV / GitHub Security Advisories; osv)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-115923; retrieved 2026-11-02; source updated 2026-11-02

- OSV / GitHub Security Advisories: https://osv.dev/vulnerability/GHSA-w658-mh9p-ww8f; retrieved 2026-11-02; source updated 2026-10-28

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-115923; retrieved 2026-11-02; source updated Not reported

Revision: 7d1a39c2eaad5df1cc3e57f0ce23b2a4ef4473ef082f91cb68ac8727b6080b9f

Canonical: https://y2.dev/cve/CVE-2026-115923

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