MediumCVE-2026-115923

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

    Published Last modified Sources: OSV, Hersteller, CVE.org

    What is affected, what to do

    Update Backstage to version 3.9.2.

    Affected
    • Backstage gte 4.0.0, < 4.0.2..*
    • Backstage lt *..3.9.2
    Fixed in
    • Backstage 3.9.2

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    6.5

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: Vendor (CNA), CVSS v3

    6.5

    CVSS v3

    Severity Medium on the scale from 0 to 10.

    Source: OSV, Hersteller, CVE.org

    0.3 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 24.6

    Show all metrics
    Severity
    Medium
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    67.34 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    no public PoC known
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    6.5 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    6.5
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    0.3 %
    Low — model estimates < 1% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    24.6
    Elevated — this CVE ranks above at least 10% of all CVEs scored today.
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    —
    Published
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-22

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    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://<host>/trusted/%2e%2e/attacker/repo/blob/main/catalog-info.yaml matches a https://<host>/trusted/** pattern as a raw string, but resolves to and is fetched from https://<host>/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.

    Source: OSV (Open Source Vulnerabilities), GitHub Security Advisories, cvelistv5, NVD (NIST)

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    backstagebackstage
    • ≥ 4.0.0, < 4.0.2
    • < 3.9.2
    • —
    • 3.9.2
    npm@backstage/plugin-catalog-backend
    • < 3.9.2
    • >= 4.0.0, < 4.0.2
    • 4.0.0
    • —
    • 3.9.2
    • 4.0.2
    • 4.0.2
    • 3.9.2

    Vendors and products

    Weakness classes (CWE)

    • CWE-22Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

      Base

      The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.

      Entry at MITRE CWE-22

    References & sources

    • github.combackstage/backstage/commit/3214dc8f15d4a08a2fd07a72a8fe4d00aeac…x_refsource_MISC, web
    • github.combackstage/backstage/commit/737ff1c719dbd5a97f375b7f1db6d6141661…x_refsource_MISC, web
    • github.combackstage/backstage/releases/tag/v1.54.10x_refsource_MISC, web
    • github.combackstage/backstage/releases/tag/v1.56.1x_refsource_MISC, web
    • github.combackstage/backstage/security/advisories/GHSA-w658-mh9p-ww8fx_refsource_CONFIRM, web
    • NVD (NIST)vuln/detail/CVE-2026-115923advisory
    • github.combackstage/backstagepackage

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    1. ReceivedGitHub

      CVSS V3.1: AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N

      Weakness type: CWE-22

      Description added or changed

      Show 9 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionadded
      —
      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.
      CVSSadded
      —
      AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
      Weakness type (CWE)added
      —
      CWE-22
      Affected versions (publisher)added
      —
      New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/115xxx/CVE-2026-115923.json">CVE-2026-115923</a>
      Referenceadded
      —
      https://github.com/backstage/backstage/commit/3214dc8f15d4a08a2fd07a72a8fe4d00aeac0db4
      Referenceadded
      —
      https://github.com/backstage/backstage/commit/737ff1c719dbd5a97f375b7f1db6d61416618419
      Referenceadded
      —
      https://github.com/backstage/backstage/releases/tag/v1.54.10
      Referenceadded
      —
      https://github.com/backstage/backstage/releases/tag/v1.56.1
      Referenceadded
      —
      https://github.com/backstage/backstage/security/advisories/GHSA-w658-mh9p-ww8f

      Source identifier: security-advisories@github.com

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