CVE-2021-43776

mediumpriority · track · 24EPSS 0.007 · 52 %ileEUUS

grimoire priorityP3 · Track

Exploitable?

—

no known exploitation

Likely / severe?

0.68% (52nd) EPSS

CVSS 4.3 · medium

Is it mine?

3 products

Check your exposure

Who says so?

4 sources

cnnvd · enisa_euvd · nvd · osv

EPSS · scored 2026-10-28

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`.

cvss

Technical severity, 0–10. One row per scoring source.

7.4

010

base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · medium–high · 4.3–7.4

v2.04.3mediumAV:N/AC:M/Au:N/C:N/I:P/A:Nprimary · NVD / NIST USexploitability 8.6 · impact 2.9

v3.16.1mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:Nprimary · NVD / NIST USexploitability 2.8 · impact 2.7

v3.17.4highCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:Nsecondary · ENISA EU

v3.17.4highCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:Nsecondary · security-advisories@github.comexploitability 2.8 · impact 4

v3.17.4highCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:Nsecondary · OSV

v3.15.6mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N/E:Usecondary · CVSS-BT (t0sche)

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-79USCWE-79US

affected products (3)

Products and version ranges known to be affected.

backstage backstage≤ < 0.4.9enisa_euvdEU
linuxfoundation auth backend< 0.4.9nvdUScpe:2.3:a:linuxfoundation:auth_backend:*:*:*:*:*:*:*:*
npm @backstage/plugin-auth-backend< 0.4.9osvUSpkg:npm/%40backstage/plugin-auth-backend

advisories (1)

Vendor and ecosystem advisories describing this.

GHSA-w7fj-336r-vw49Cross-Site Scripting vulnerability in @backstage/plugin-auth-backend2021-12-01ghsa · osvUS
### Impact This vulnerability 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. ### Patches This is vulnerability is patched in version `0.4.9` of `@backstage/plugin-auth-backend`. ### For more information If you have any questions or comments about this advisory: * Open an issue in the [Backstage repository](https://github.com/backstage/backstage) * Visit our chat, linked to in [Backstage README](https://github.com/backstage/backstage)

also known as (3)

Other names and identifiers for this entity.

sources

Which sources assert this record, and when.

cnnvd enisa_euvd nvd osv NVD CVE.org MITRE

published 2021-11-26modified 2026-06-17

references (7)

External citations — patches, advisories, analysis.

scry

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