High-Severity Bug Reported in Google’s OAuth Client Library for Java

Google last month addressed a high-severity flaw in its OAuth client library for Java that could be abused by a malicious actor with a compromised token to deploy arbitrary payloads.

Tracked as CVE-2021-22573, the vulnerability is rated 8.7 out of 10 for severity and relates to an authentication bypass in the library that stems from an improper verification of the cryptographic signature.

Credited with discovering and reporting the flaw on March 12 is Tamjid Al Rahat, a fourth-year Ph.D. student of Computer Science at the University of Virginia, who has been awarded $5,000 as part of Google’s bug bounty program.

“The vulnerability is that the IDToken verifier does not verify if the token is properly signed,” an advisory for the flaw reads.

“Signature verification makes sure that the token’s payload comes from a valid provider, not from someone else. An attacker can provide a compromised token with custom payload. The token will pass the validation on the client side.”

The open-source Java library, built on the Google HTTP Client Library for Java, makes it possible to obtain access tokens to any service on the web that supports the OAuth authorization standard.

Google, in its README file for the project on GitHub, notes that the library is supported in maintenance mode and that it’s only fixing necessary bugs, indicative of the severity of the vulnerability.

Users of the google-oauth-java-client library are recommended to update to version 1.33.3, released on April 13, to mitigate any potential risk.

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