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© 2026 FAUCET Technologies LLC. All rights reserved.

CVE-2021-43776

21
FAUCET Score

CVE-2021-43776 is a cross-site scripting (XSS) vulnerability in the auth-backend plugin of Backstage, an open platform for building developer portals. A malicious actor could trick a user into visiting a specially crafted URL, leading to XSS and potential exfiltration of access tokens or other secrets. The vulnerability has a CVSS score of 6.1 (Medium), indicating a network-based attack with low complexity requiring user interaction, resulting in low confidentiality and integrity impacts. While the default Content Security Policy (CSP) mitigates this, deployments with disabled CSPs are vulnerable. There is no evidence of active exploitation, public exploit code, or significant community discussion surrounding this CVE.

Impacted Technologies

VendorProductVersion(s)CPE
< 0.4.9CPE matchmatch criteria
cpe:2.3:a:linuxfoundation:auth_backend:*:*:*:*:*:node.js:*:*

CVSS Data

CVSS version used by this source: 3.1

7.4HIGH

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
REQUIRED
Scope
CHANGED
Confidentiality Impact
HIGH
Integrity Impact
NONE
Availability Impact
NONE
Exploitability Score
2.8
Impact Score
4.0
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.66%
Probability of exploitation in next 30 days
EPSS Percentile
47.7%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0066 is in the 52nd percentile among its peer group of 26,221 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.0 Mastodon, and 0.1 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (1)

npmpatch availablevia ghsa
Product: @backstage/plugin-auth-backendFixed in: 0.4.9

Vendor Advisories (1)

npmGHSA-w7fj-336r-vw49high

Cross-Site Scripting vulnerability in @backstage/plugin-auth-backend

Dec 1, 2021

References

github.com / backstage/backstage/security/advisories/GHSA-w7fj-336r-vw49
Third Party Advisory
github.com / backstage/backstage/tree/master/plugins/auth-backend
ProductThird Party Advisory