CVE-2023-36820 is a medium-severity (CVSS 4.8) CWE-284 vulnerability in io.micronaut.security:micronaut-security-oauth2. 1 public exploit reference exists, so weaponization risk is real. A fix is available for io.micronaut.security:micronaut-security-oauth2 — see the affected versions and patch details below.
micronaut security has invalid IdTokenClaimsValidator logic on aud
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for CVE-2023-36820.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2023-36820 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,156 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
io.micronaut.security:micronaut-security-oauth2☕io.micronaut.security:micronaut-security-oauth2☕io.micronaut.security:micronaut-security-oauth2☕io.micronaut.security:micronaut-security-oauth2☕io.micronaut.security:micronaut-security-oauth2☕io.micronaut.security:micronaut-security-oauth2☕io.micronaut.security:micronaut-security-oauth2☕io.micronaut.security:micronaut-security-oauth2+3 moreReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
Description
Summary
IdTokenClaimsValidator skips aud claim validation if token is issued by same identity issuer/provider.
Details
This logic violates point 3 of https://openid.net/specs/openid-connect-core-1_0.html#IDTokenValidation.
Workaround exists by setting micronaut.security.token.jwt.claims-validators.audience with valid values.
micronaut.security.token.jwt.claims-validators.openid-idtoken can be kept as default on.
PoC
Should probably be:
return issuer.equalsIgnoreCase(iss) &&
audiences.contains(clientId) &&
validateAzp(claims, clientId, audiences);
Impact
Any OIDC setup using Micronaut where multiple OIDC applications exists for the same issuer but token auth are not meant to be shared.
Mitigation
Please upgrade to a patched micronaut-security-oauth2 release as soon as possible.
If you cannot upgrade, for example, if you are still using Micronaut Framework 2, you can patch your application by creating a replacement of IdTokenClaimsValidatorReplacement
package cve;
import io.micronaut.context.annotation.Replaces;
import io.micronaut.context.annotation.Requires;
import io.micronaut.core.annotation.NonNull;
import io.micronaut.core.util.StringUtils;
import io.micronaut.security.config.SecurityConfigurationProperties;
import io.micronaut.security.oauth2.client.IdTokenClaimsValidator;
import io.micronaut.security.oauth2.configuration.OauthClientConfiguration;
import io.micronaut.security.oauth2.configuration.OpenIdClientConfiguration;
import io.micronaut.security.token.jwt.generator.claims.JwtClaims;
import io.micronaut.security.token.jwt.validator.JwtClaimsValidatorConfigurationProperties;
import javax.inject.Singleton;
import java.net.URL;
import java.util.Collection;
import java.util.List;
import java.util.Optional;
@Requires(property = SecurityConfigurationProperties.PREFIX + ".authentication", value = "idtoken")
@Requires(property = JwtClaimsValidatorConfigurationProperties.PREFIX + ".openid-idtoken", notEquals = StringUtils.FALSE)
@Singleton
@Replaces(IdTokenClaimsValidator.class)
public class IdTokenClaimsValidatorReplacement extends IdTokenClaimsValidator {
public IdTokenClaimsValidatorReplacement(Collection<OauthClientConfiguration> oauthClientConfigurations) {
super(oauthClientConfigurations);
}
@Override
protected boolean validateIssuerAudienceAndAzp(@NonNull JwtClaims claims,
@NonNull String iss,
@NonNull List<String> audiences,
@NonNull String clientId,
@NonNull OpenIdClientConfiguration openIdClientConfiguration) {
if (openIdClientConfiguration.getIssuer().isPresent()) {
Optional<URL> issuerOptional = openIdClientConfiguration.getIssuer();
if (issuerOptional.isPresent()) {
String issuer = issuerOptional.get().toString();
return issuer.equalsIgnoreCase(iss) &&
audiences.contains(clientId) &&
validateAzp(claims, clientId, audiences);
}
}
return false;
}
}
``
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | io.micronaut.security:micronaut-security-oauth2 | ≥ 3.11.0&&< 3.11.1 | 3.11.1io.micronaut.security:micronaut-security-oauth2:3.11.1 |
| ☕Maven | io.micronaut.security:micronaut-security-oauth2 | ≥ 3.10.0&&< 3.10.2 | 3.10.2io.micronaut.security:micronaut-security-oauth2:3.10.2 |
| ☕Maven | io.micronaut.security:micronaut-security-oauth2 | ≥ 3.9.0&&< 3.9.6 | 3.9.6io.micronaut.security:micronaut-security-oauth2:3.9.6 |
| ☕Maven | io.micronaut.security:micronaut-security-oauth2 | ≥ 3.8.0&&< 3.8.4 | 3.8.4io.micronaut.security:micronaut-security-oauth2:3.8.4 |
| ☕Maven | io.micronaut.security:micronaut-security-oauth2 | ≥ 3.7.0&&< 3.7.4 | 3.7.4io.micronaut.security:micronaut-security-oauth2:3.7.4 |
| ☕Maven | io.micronaut.security:micronaut-security-oauth2 | ≥ 3.6.0&&< 3.6.6 | 3.6.6io.micronaut.security:micronaut-security-oauth2:3.6.6 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for io.micronaut.security:micronaut-security-oauth2, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update io.micronaut.security:micronaut-security-oauth2 to 3.11.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-36820 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2023-36820 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2023-36820. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2023-36820 in your dependencies?
O3 Security finds CVE-2023-36820 across Maven dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.