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Response snapshot Oct 29, 2026, 01:26 UTC

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VulnerabilityCVE-2026-115923

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

@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.

At a glance

Exploited
Not known
Severity
6.5 Medium (CVSS 3.1)
Chance of exploitation
Not estimated
Sources
1 source

What to do

GitHub lists first patched versions: @backstage/plugin-catalog-backend: 3.9.2; @backstage/plugin-catalog-backend: 4.0.2. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-w658-mh9p-ww8f (opens a new tab)

What happened

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.

Continue reading

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 content is read.

An authenticated user with permission to register catalog locations (catalog.location.create) can use this to have an entity from an untrusted source admitted as if it originated from a trusted location scope.

Impact

The crossed boundary is the operator-configured catalog ingestion policy: entity content from outside the trusted location scope is ingested as if it were within it. Downstream consequences depend on deployment configuration, for example actions taken with integration credentials by processors or scaffolder when acting on the ingested entity. The assessment of this report found no basis for impact claims beyond the ingestion policy boundary itself.

Patches

This is fixed in @backstage/plugin-catalog-backend 3.9.2 (Backstage release 1.54.10) and 4.0.2 (Backstage release 1.56.1). Version 4.0.1 as published is not fixed.

Workarounds

No complete workaround is available for deployments that rely on URL location patterns to restrict catalog kinds. Restricting location registration permissions reduces exposure.

Affected package ranges reported by GitHub: @backstage/plugin-catalog-backend: < 3.9.2 @backstage/plugin-catalog-backend: >= 4.0.0, < 4.0.2

Scores and how they were measured

CVSS base severity

6.5

Version 3.1As of

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

Not available

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-w658-mh9p-ww8f (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-w658-mh9p-ww8f, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 28). Backstage catalog rules can be bypassed for URL locations using encoded path segments (CVE-2026-115923). https://kevwire.com/record/CVE-2026-115923

MLA

"Backstage catalog rules can be bypassed for URL locations using encoded path segments (CVE-2026-115923)." KEVWire, 28 Oct. 2026, kevwire.com/record/CVE-2026-115923.

Chicago

KEVWire. "Backstage catalog rules can be bypassed for URL locations using encoded path segments (CVE-2026-115923)." Last modified October 28, 2026. https://kevwire.com/record/CVE-2026-115923.

Evidence summary (plain text)

Backstage catalog rules can be bypassed for URL locations using encoded path segments (Oct 28, 2026).
@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.

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.
CVSS 6.5 (version 3.1; evidence as of Oct 28, 2026; https://github.com/advisories/GHSA-w658-mh9p-ww8f).
Sources:
GitHub-reviewed advisory GHSA-w658-mh9p-ww8f: https://github.com/advisories/GHSA-w658-mh9p-ww8f
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
Record ID: CVE-2026-115923.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 29, 2026, 00:55 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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