Summary
google-oauth-java-client improperly verifies cryptographic signature
The vulnerability impacts only users of the IdTokenVerifier class. The verify method in IdTokenVerifier does not validate the signature before verifying the claims (e.g., iss, aud, etc.). Signature verification makes sure that the token's payload comes from valid provider, not from someone else.
An attacker can provide a compromised token with modified payload like email or phone number. The token will pass the validation by the library. Once verified, modified payload can be used by the application.
If the application sends verified IdToken to other service as is like for auth - the risk is low, because the backend of the service is expected to check the signature and fail the request.
Reporter: Tamjid al Rahat, contributor
Proof of Concept
To reproduce, one needs to call the verify function with an IdToken instance that contains a malformed signature to successfully bypass the checks inside the verify function.
/** A default http transport factory for testing */
static class DefaultHttpTransportFactory implements HttpTransportFactory {
public HttpTransport create() {
return new NetHttpTransport();
}
}
// The below token has some modified bits in the signature
private static final String SERVICE_ACCOUNT_RS256_TOKEN_BAD_SIGNATURE =
"eyJhbGciOiJSUzI1NiIsImtpZCI6IjJlZjc3YjM4YTFiMDM3MDQ4NzA0MzkxNmFjYmYyN2Q3NG" +
"VkZDA4YjEiLCJ0eXAiOiJKV1QifQ.eyJhdWQiOiJodHRwczovL2V4YW1wbGUuY29tL2F1ZGllbm" +
"NlIiwiZXhwIjoxNTg3NjMwNTQzLCJpYXQiOjE1ODc2MjY5NDMsImlzcyI6InNvbWUgaXNzdWVy" +
"Iiwic3ViIjoic29tZSBzdWJqZWN0In0.gGOQW0qQgs4jGUmCsgRV83RqsJLaEy89-ZOG6p1u0Y26" +
"FyY06b6Odgd7xXLsSTiiSnch62dl0Lfi9D0x2ByxvsGOCbovmBl2ZZ0zHr1wpc4N0XS9lMUq5RJ" +
"QbonDibxXG4nC2zroDfvD0h7i-L8KMXeJb9pYwW7LkmrM_YwYfJnWnZ4bpcsDjojmPeUBlACg7tjjOgBFby" +
"QZvUtaERJwSRlaWibvNjof7eCVfZChE0PwBpZc_cGqSqKXv544L4ttqdCnm0NjqrTATXwC4gYx" +
"ruevkjHfYI5ojcQmXoWDJJ0-_jzfyPE4MFFdCFgzLgnfIOwe5ve0MtquKuv2O0pgvg";
IdTokenVerifier tokenVerifier =
new IdTokenVerifier.Builder()
.setClock(clock)
.setCertificatesLocation("https://www.googleapis.com/robot/v1/metadata/x509/integration-tests%40chingor-test.iam.gserviceaccount.com")
.setHttpTransportFactory(new DefaultHttpTransportFactory())
.build();
// verification will return true despite modified signature for versions <1.33.3
tokenVerifier.verify(IdToken.parse(GsonFactory.getDefaultInstance(), SERVICE_ACCOUNT_RS256_TOKEN_BAD_SIGNATURE));
Remediation and Mitigation
Update to the version 1.33.3 or higher
If the library used indirectly or cannot be updated for any reason you can use similar IdToken verifiers provided by Google that already has signature verification. For example:
google-auth-library-java
google-api-java-client
Timeline
Date reported: 12 Dec 2021
Date fixed: 13 Apr 2022
Date disclosed: 2 May 2022
For more information
If you have any questions or comments about this advisory:
- Open an issue in the google-oauth-java-client repo
Impact
CVE-2021-22573 has a CVSS score of 7.3 (High). The vector is network-reachable, low privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.33.3); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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See it in your environmentNew to Kodem? Get a demo →Remediation advice
The issue was fixed in the 1.33.3 version of the library
Frequently Asked Questions
- What is CVE-2021-22573? CVE-2021-22573 is a high-severity security vulnerability in com.google.oauth-client:google-oauth-client (maven), affecting versions >= 1.16.0-rc, < 1.33.3. It is fixed in 1.33.3.
- How severe is CVE-2021-22573? CVE-2021-22573 has a CVSS score of 7.3 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of com.google.oauth-client:google-oauth-client are affected by CVE-2021-22573? com.google.oauth-client:google-oauth-client (maven) versions >= 1.16.0-rc, < 1.33.3 is affected.
- Is there a fix for CVE-2021-22573? Yes. CVE-2021-22573 is fixed in 1.33.3. Upgrade to this version or later.
- Is CVE-2021-22573 exploitable, and should I be worried? Whether CVE-2021-22573 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2021-22573 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2021-22573? Upgrade
com.google.oauth-client:google-oauth-clientto 1.33.3 or later.