CVE-2021-43776 json
XSS vulnerability in @backstage/plugin-auth-backend
published 2021-11-26 4 y ago modified 2026-06-17 4 mo ago also GHSA-w7fj-336r-vw49 , EUVD-2021-2600
- cvss
- 7.4
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.7%
- EPSS 0.7% chance of exploitation in 30 days, percentile 52%
- public exploits
- 0
- none known
Summary
Backstage is an open platform for building developer portals. In affected versions the auth-backend plugin allows a malicious actor to trick another user into visiting a vulnerable URL that executes an XSS attack. This attack can potentially allow the attacker to exfiltrate access tokens or other secrets from the user's browser. The default CSP does prevent this attack, but it is expected that some deployments have these policies disabled due to incompatibilities. This is vulnerability is patched in version `0.4.9` of `@backstage/plugin-auth-backend`.
Patch / fix
- npm @backstage/plugin-auth-backend 0.4.9
- linuxfoundation auth_backend 0.4.9
Exploit prediction
0.68% chance of exploitation in the next 30 days, higher than 52% of all scored CVEs (FIRST EPSS, 2026-11-08).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 7.4 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:N |
| NVD | 3.1 | 6.1 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N |
| NVD | 2.0 | 4.3 | AV:N/AC:M/Au:N/C:N/I:P/A:N |
| GitHub | 3.1 | 7.4 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:N |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| npm | @backstage/plugin-auth-backend | <0.4.9 |
0.4.9 |
Affected products
- backstage backstage
Classification
- Weakness
-
- CWE-79 Improper Neutralization of Input During Web Page Generation
References
-
github.com
/backstage/backstage/security/advisories/GHSA-w7fj-336r-vw49
web, third-party-advisory
-
github.com
/backstage/backstage/tree/master/plugins/auth-backend
web, product, third-party-advisory
-
nvd.nist.gov
/vuln/detail/CVE-2021-43776
advisory
-
github.com
/backstage/backstage
package
Sources
- CVE List CVE-2021-43776
- GitHub Advisory GHSA-w7fj-336r-vw49
- NVD CVE-2021-43776
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