CVE-2021-43776 XSS vulnerability in @backstage/plugin-auth-backend
Attackers can execute XSS via malicious URLs in Backstage auth-backend, potentially stealing access tokens if CSP is disabled.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2021-43776?
CVE-2021-43776 is a high-severity cross-site scripting vulnerability in backstage, published on 26 Nov 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
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`.
Weakness: CWE-79
Which versions are affected by CVE-2021-43776?
2 open source packages ship an affected version, including @backstage/plugin-auth-backend. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
@backstage/plugin-auth-backend npm | All versions | 0.4.9 |
@backstage/plugin-auth-backend npm | All versions | 0.4.9 |
Products include Linuxfoundation Auth Backend.
How do I fix CVE-2021-43776?
Upgrade @backstage/plugin-auth-backend to 0.4.9 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2021-43776 being exploited?
There is no known exploitation of CVE-2021-43776 in the wild and no public exploit code.
Sources
Also known as GHSA-w7fj-336r-vw49.