Multiple critical vulnerabilities in Authlib allow attackers to forge trusted JWT tokens (CVE-2026-27962, CVSS 9.1), recover sensitive information from RSA1_5 encrypted tokens (CVE-2026-28490, CVSS 6.5), and bypass OpenID Connect token integrity checks (CVE-2026-28498, CVSS 7.5). These flaws affect all Authlib versions prior to 1.6.9 and require immediate patching. The fix for all three issues is to upgrade to Authlib version 1.6.9.
Jay Neiva and Mauro Carrillo discovered that Authlib did not properly validate cryptographic keys embedded in JWT headers. An attacker could possibly use this issue to forge trusted tokens, resulting in authentication and authorization bypass. (CVE-2026-27962) Jay Neiva and Mauro Carrillo discovered that Authlib incorrectly handled RSA1_5 encrypted tokens. An attacker could possibly use this issue to recover sensitive encrypted information, resulting in information disclosure. (CVE-2026-28490) Jay Neiva and Mauro Carrillo discovered that Authlib did not properly reject unsupported cryptographic algorithms when validating OpenID Connect ID tokens. An attacker could possibly use this issue to bypass token integrity checks, resulting in authentication bypass. (CVE-2026-28498) Johnny Deuss discovered that Authlib did not provide cross-site request forgery protection for the OAuth cache feature in its Starlette integration. An attacker could possibly use this issue to perform unauthorized OAuth actions, resulting in cross-site request forgery. This issue only affected Ubuntu 24.04 LTS and Ubuntu 26.04 LTS. (CVE-2026-41425)