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CVE-2026-28802

Authlib: Setting `alg: none` and a blank signature appears to bypass signature verification

CVSS 4.0 7.7 HIGHCheck source for fixed versionsKEV status unknown

Original advisory

cve-program · CVE-2026-28802

Published

Authlib is a Python library which builds OAuth and OpenID Connect servers. From version 1.6.5 to before version 1.6.7, previous tests involving passing a malicious JWT containing alg: none and an empty signature was passing the signature verification step without any changes to the application code when a failure was expected.. This issue has been patched in version 1.6.7.

Read the publisher's advisory

Affected versions, risk and source history

cve-program · CVE-2026-28802

Published

authlib

Vendor product

Publisher's version information

Shown as published. These rules are not interpreted as NuGet package version ranges.

{
                    "vendor": "authlib",
                    "product": "authlib",
                    "versions": [
                        {
                            "version": ">= 1.6.5, < 1.6.7",
                            "status": "affected"
                        }
                    ]
                }

Original source record · Cite this exact observation · Complete original publisher JSON