Vulnerability-Lookup

CVE-2026-73563 (GCVE-0-2026-73563)

Vulnerability from cvelistv5 – Published: 2026-08-13 17:32 – Updated: 2026-08-13 18:07

Title

Backstage: Unauthenticated OAuth account takeover via `redirect_uri` allowlist bypass in `@backstage/plugin-auth-backend`

Summary

Backstage is an open framework for building developer portals. Prior to 0.29.2, the experimental dynamic client registration and client ID metadata document features in the @backstage/plugin-auth-backend use full-string matcher.isMatch glob matching for auth.experimentalDynamicClientRegistration.allowedRedirectUriPatterns and the auth.experimentalClientIdMetadataDocuments allowedClientIdPatterns and allowedRedirectUriPatterns options. A hostname wildcard can match across URL component boundaries, allowing an attacker-controlled redirect URI with a trusted hostname suffix in its path to pass the allowlist and receive an OAuth authorization code after a victim completes the flow. Patterns without an explicit protocol can match unintended protocols, and redirect URIs containing embedded credentials are accepted after user information is stripped for matching. The features are experimental and disabled by default; only deployments that enable them and configure custom wildcard-hostname or protocol-less patterns are affected. This issue is first fixed in prerelease version 0.29.2.

Severity

4.7 (Medium)


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

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-08-13 18:07 UTC

CWE

CWE-601 - URL Redirection to Untrusted Site ('Open Redirect')

Assigner

GitHub_M CNA under the mitre root

CNA scorecard C 72/100 over 7886 records in the last 180 days details

References

1 reference

URL	Tags
https://github.com/backstage/backstage/security/a…	x_refsource_CONFIRM

Impacted products

1 product

Vendor	Product	Version	CPE status
backstage	backstage	Affected: < 0.29.2	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-73563

Vulnerability from fkie_nvd - Published: 2026-08-13 18:18 - Updated: 2026-10-15 20:37

Severity

4.7 (Medium) - CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:N/A:N
6.1 (Medium) - CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/backstage/backstage/security/advisories/GHSA-38hq-7x33-php4	Mitigation, Vendor Advisory

Impacted products

	Vendor	Product	Version
	linuxfoundation	backstage\/plugin-auth-backend	*

JSON

To clipboard

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GHSA-38HQ-7X33-PHP4

Vulnerability from github – Published: 2026-07-24 16:20 – Updated: 2026-08-13 17:32

Summary

@backstage/plugin-auth-backend: Unauthenticated OAuth account takeover via `redirect_uri` allowlist bypass

Details

Impact

The allowlist matching used by the experimental dynamic client registration and client ID metadata document (CIMD) features in @backstage/plugin-auth-backend matched glob patterns against the full URL string. A * wildcard could therefore match across URL component boundaries: a pattern such as https://*.example.com/callback, intended to allow subdomains of a trusted host, would also match an attacker-controlled URL such as https://attacker.example/x.example.com/callback. This applies to auth.experimentalDynamicClientRegistration.allowedRedirectUriPatterns as well as the allowedClientIdPatterns and allowedRedirectUriPatterns options of auth.experimentalClientIdMetadataDocuments.

An attacker could use this to register an OAuth client whose redirect URI points to a host they control while still passing the allowlist, causing authorization codes to be delivered to the attacker when a victim completes an authorization flow. In addition, allowlist patterns without an explicit protocol could match URLs with any protocol, and redirect URIs containing embedded credentials (user:pass@host) were accepted after the credentials were stripped for matching.

The practical impact is limited. Both features are experimental and disabled by default, and the default allowlist patterns only reference fixed or loopback hosts and are not affected. Deployments are only impacted if they enable one of these features and configure custom allowlist patterns that contain a wildcard in the hostname, or patterns without an explicit protocol.

Patches

Patched in @backstage/plugin-auth-backend version 0.29.2. Patterns are now matched against each URL component separately so that wildcards no longer match across the host and path boundary, patterns without an explicit protocol are rejected as invalid configuration, and redirect URIs with embedded credentials are always rejected.

Note that as part of this fix, a wildcard port no longer implicitly matches every path: a pattern such as http://localhost:* now only matches the root path. Use http://localhost:*/* to allow any port and any path.

Workarounds

Disable the experimental features by removing auth.experimentalDynamicClientRegistration and auth.experimentalClientIdMetadataDocuments from your app-config, which is the default configuration. Alternatively, restrict the configured allowlist patterns to fully specified URLs with an explicit protocol and no wildcard in the hostname, which are not affected by this vulnerability.

Severity

4.7 (Medium)


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

Show details on source website

JSON

To clipboard

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    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Impact\nThe allowlist matching used by the experimental dynamic client registration and client ID metadata document (CIMD) features in `@backstage/plugin-auth-backend` matched glob patterns against the full URL string. A * wildcard could therefore match across URL component boundaries: a pattern such as `https://*.example.com/callback`, intended to allow subdomains of a trusted host, would also match an attacker-controlled URL such as `https://attacker.example/x.example.com/callback`. This applies to `auth.experimentalDynamicClientRegistration.allowedRedirectUriPatterns` as well as the `allowedClientIdPatterns` and `allowedRedirectUriPatterns` options of `auth.experimentalClientIdMetadataDocuments`.\n\nAn attacker could use this to register an OAuth client whose redirect URI points to a host they control while still passing the allowlist, causing authorization codes to be delivered to the attacker when a victim completes an authorization flow. In addition, allowlist patterns without an explicit protocol could match URLs with any protocol, and redirect URIs containing embedded credentials (user:pass@host) were accepted after the credentials were stripped for matching.\n\nThe practical impact is limited. Both features are experimental and disabled by default, and the default allowlist patterns only reference fixed or loopback hosts and are not affected. Deployments are only impacted if they enable one of these features and configure custom allowlist patterns that contain a wildcard in the hostname, or patterns without an explicit protocol.\n\n### Patches\nPatched in `@backstage/plugin-auth-backend` version `0.29.2`. Patterns are now matched against each URL component separately so that wildcards no longer match across the host and path boundary, patterns without an explicit protocol are rejected as invalid configuration, and redirect URIs with embedded credentials are always rejected.\n\nNote that as part of this fix, a wildcard port no longer implicitly matches every path: a pattern such as `http://localhost:*` now only matches the root path. Use `http://localhost:*/*` to allow any port and any path.\n\n### Workarounds\nDisable the experimental features by removing `auth.experimentalDynamicClientRegistration` and `auth.experimentalClientIdMetadataDocuments` from your `app-config`, which is the default configuration. Alternatively, restrict the configured allowlist patterns to fully specified URLs with an explicit protocol and no wildcard in the hostname, which are not affected by this vulnerability.",
  "id": "GHSA-38hq-7x33-php4",
  "modified": "2026-08-13T17:32:47Z",
  "published": "2026-07-24T16:20:59Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/backstage/backstage/security/advisories/GHSA-38hq-7x33-php4"
    },
    {
      "type": "WEB",
      "url": "https://github.com/backstage/backstage/commit/274acc51d22a7dd919cdda49d9086cf12c0b8711"
    },
    {
      "type": "WEB",
      "url": "https://github.com/backstage/backstage/commit/6370e53bce8b227c63092300594ffde29c006886"
    },
    {
      "type": "WEB",
      "url": "https://github.com/backstage/backstage/commit/ef606a85545cb6d765e20afd1ff43ae5407a3660"
    },
    {
      "type": "WEB",
      "url": "https://github.com/backstage/backstage/commit/fdc0d2dcd9a571e3839d7f5de4133c4e242a3a41"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/backstage/backstage"
    },
    {
      "type": "WEB",
      "url": "https://github.com/backstage/backstage/releases/tag/v1.53.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:N/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "@backstage/plugin-auth-backend: Unauthenticated OAuth account takeover via `redirect_uri` allowlist bypass"
}

RHSA-2026:65118

Vulnerability from csaf_redhat - Published: 2026-09-08 07:34 - Updated: 2026-11-13 13:37

Summary

Red Hat Security Advisory: Ansible plug-ins for Red Hat Developer Hub Product Release Update

Severity

Important

Scope

16 vulnerabilities in this advisory, including CVE-2026-73563.

CVE-2026-73563

A flaw was found in the `@backstage/plugin-auth-backend` component of Backstage. This vulnerability allows an unauthenticated remote attacker to bypass the `redirect_uri` allowlist in the experimental dynamic client registration feature. By crafting a malicious redirect Uniform Resource Identifier (URI) with a trusted hostname suffix, an attacker can receive an OAuth authorization code, potentially leading to an account takeover. This issue affects deployments that have enabled the experimental features and configured custom wildcard-hostname or protocol-less patterns.

4.7 (Medium)


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

Fixed: 1 product

https://access.redhat.com/errata/RHSA-2026:65118

Open the full advisory

RHSA-2026:65155

Vulnerability from csaf_redhat - Published: 2026-09-08 08:56 - Updated: 2026-11-13 13:37

Summary

Red Hat Security Advisory: Ansible plug-ins for Red Hat Developer Hub Product Release Update

Severity

Important

Scope

11 vulnerabilities in this advisory, including CVE-2026-73563.

CVE-2026-73563

4.7 (Medium)


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

Fixed: 1 product

https://access.redhat.com/errata/RHSA-2026:65155

Open the full advisory

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

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Sightings and recorded dates, grouped by day · UTC

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Following the VTEM framework (Black Hat USA 2015), time to patch starts when the vendor or a coordinator was informed, total time to patch at discovery, and disclosure to patch at public disclosure; vendor response time runs from the report to its acknowledgement. Time to exploit and time unpatched start at the earliest discovery or report, falling back to public disclosure. Unpatched time ends at the first recorded patch, or the calculation time when no patch is recorded. Exploitation to patch shows the interval between those two events; a published proof of concept is a public exploit, not exploitation.

Each result shows its source dates. A negative interval means the end event came first; when date-only inputs leave the order open, the result says so. Date-only inputs are approximate. The earliest evidence wins: KEV report dates and sightings are labelled as such. Records describing another vulnerability are listed but never calculated from, and a PoC alone does not establish exploitation. Missing patch evidence does not prove that no patch exists. Filters below change the event list only.

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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

CVE-2026-73563 (GCVE-0-2026-73563)

FKIE_CVE-2026-73563

GHSA-38HQ-7X33-PHP4

Impact

Patches

Workarounds

RHSA-2026:65118

RHSA-2026:65155

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Related by attack behaviour