@backstage/plugin-auth-backend: OAuth redirect URI allowlist bypass

published 2026-03-12 7 mo ago modified 2026-06-17 4 mo ago also GHSA-wqvh-63mv-9w92 , EUVD-2026-11671

cvss: 5.9; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.2%; EPSS 0.2% chance of exploitation in 30 days, percentile 6%
public exploits: 0; none known

Backstage is an open framework for building developer portals. Prior to 0.27.1, the experimental OIDC provider in @backstage/plugin-auth-backend is vulnerable to a redirect URI allowlist bypass. Instances that have enabled experimental Dynamic Client Registration or Client ID Metadata Documents and configured allowedRedirectUriPatterns are affected. A specially crafted redirect URI can pass the allowlist validation while resolving to an attacker-controlled host. If a victim approves the resulting OAuth consent request, their authorization code is sent to the attacker, who can exchange it for a valid access token. This requires victim interaction and that one of the experimental features is explicitly enabled, which is not the default. This vulnerability is fixed in 0.27.1.

Patch / fix

fixed in 1 links 1

npm @backstage/plugin-auth-backend 0.27.1

github.com/backstage/backstage@6042dd0 commit

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-32235 updated 2026-09-21 cvss 5.9

@backstage/plugin-auth-backend: @backstage/plugin-auth-backend: OAuth redirect URI allowlist bypass

Red Hat Self-service automation portal 2 ansible-automation-platform/automation-portal
affected: workaround, no fix available “Fix deferred”
Red Hat Developer Hub 1.10 rhdh/rhdh-hub-rhel9 1780930740
fixed: vendor fix RHSA-2026:24841
Red Hat Developer Hub 1.10 rhdh/rhdh-rhel9-operator 1779927546, rhdh/rhdh-operator-bundle 1780961472
not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 7 mo ago (2026-03-12)

Exploit prediction

0.17% chance of exploitation in the next 30 days, higher than 6% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	5.9	CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:L/A:N
NVD	3.1	4.7	CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N
GitHub	3.1	5.9	CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:L/A:N

Affected packages

ecosystem	package	affected	fixed in
npm	@backstage/plugin-auth-backend	<0.27.1	0.27.1

Affected products

@backstage plugin-auth-backend

Classification

Weakness

CWE-601 URL Redirection to Untrusted Site
CWE-20 Improper Input Validation

References

github.com /backstage/backstage/commit/6042dd0c7f0706e0f473dafa92799ecf19c825ec
web
github.com /backstage/backstage/security/advisories/GHSA-wqvh-63mv-9w92
web, vendor-advisory
nvd.nist.gov /vuln/detail/CVE-2026-32235
advisory
github.com /backstage/backstage
package

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary