What’s Vulnerable › Vulnerabilities

CVE-2021-44878

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.9% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2022-01-06 · updated 2026-06-17
• Weakness: CWE-347

Description

If an OpenID Connect provider supports the "none" algorithm (i.e., tokens with no signature), pac4j v5.3.0 (and prior) does not refuse it without an explicit configuration on its side or for the "idtoken" response type which is not secure and violates the OpenID Core Specification. The "none" algorithm does not require any signature verification when validating the ID tokens, which allows the attacker to bypass the token validation by injecting a malformed ID token using "none" as the value of "alg" key in the header with an empty signature value.

Affected products

• pac4j: before 4.5.5; from 5.0.0 before 5.3.1 — fixed in 4.5.5, 5.3.1

How to fix

Upgrade to a fixed version: pac4j 4.5.5, 5.3.1. Check the vendor advisory for mitigations.

References

• https://github.com/pac4j/pac4j/commit/22b82ffd702a132d9f09da60362fc6264fc281ae
• https://openid.net/specs/openid-connect-core-1_0.html#IDToken
• https://www.pac4j.org/blog/cve_2021_44878_is_this_serious.html
• https://github.com/pac4j/pac4j/commit/22b82ffd702a132d9f09da60362fc6264fc281ae
• https://openid.net/specs/openid-connect-core-1_0.html#IDToken
• https://www.pac4j.org/blog/cve_2021_44878_is_this_serious.html

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