CVE-2026-75866
CriticalCVSS 9.1Exploitation Probability (EPSS)
Low risk14th percentile - higher than 14% of all known CVEs
Summary
Punk::OAuth2::Server versions through 0.03 for Perl issue access tokens outside a client's registered scopes and grant types because no authorization path reads them. A client registered for authorization_code alone can request client_credentials, and the requested scope is signed into the token without comparison to registration. A registered client can obtain a correctly signed token with any scope, and a resource server using Punk::OAuth2::Checker accepts it.
Risk Assessment
The organization is exposed to unauthorized access to resources because a client can obtain a token with broader permissions than registered. Additionally, a client without a secret can authenticate with just its client_id, making it easier for anyone knowing that identifier to attack.
Recommendation
Update Punk::OAuth2::Server to the latest version that fixes this vulnerability. If an update is not available, restrict trust in clients and enforce scope checking in the consent hook.
Original NVD description (English source)
Punk::OAuth2::Server versions through 0.03 for Perl issue access tokens outside a client's registered scopes and grant types because no authorization path reads them. Punk::OAuth2::Server::Store registers scopes and grant_types per client and documents both as client registration. token dispatches on the grant_type in the request body, so a client registered for authorization_code alone can ask for client_credentials, and that arm passes the requested scope straight to the minter, which signs it into the at+jwt access token. authorize copies the query scope into the authorization code record without comparing it against the registration, leaving the optional consent hook as the only check between an arbitrary scope and the issued code. redirect_uris on the same client row is read and enforced. A registered client can obtain a correctly signed token carrying any scope it names, and a resource server running Punk::OAuth2::Checker accepts that token and honours the scope. A client registered without a secret authenticates on its client_id alone, so anyone who knows that identifier can request one.