CVE-2026-101274 in pretix
Summary
by MITRE • 10/28/2026
When pretix is used as the identity provider in a Single-Sign-On (SSO) setup for customer accounts, the system did not properly validate the `response_type` requested in an authorization request against the configured grant type of the SSO client. This means that if an SSO client was configured to only allow the `code` response type, which requires knowledge of the client secret to use and would wrongfully send a response type like `id_token`, it would receive back a valid token. Exploiting this requires the attacker to run JavaScript on the page specified by `redirect_uri`, which must be from a list specified in the client configuration.
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Analysis
by VulDB Data Team • 10/28/2026
The vulnerability described represents a critical flaw in the OpenID Connect implementation within pretix when it functions as an identity provider for Single-Sign-On integrations. The core technical deficiency lies in the failure to strictly validate the response_type parameter against the pre-configured grant types associated with the specific SSO client application. In standard OAuth 2.0 and OpenID Connect flows, the authorization server must ensure that the requested mode of interaction aligns with the capabilities and security policies defined for the relying party. By neglecting this validation step, pretix allows a mismatch between the intended authentication flow and the actual response generated by the identity provider. This oversight creates an opportunity for attackers to manipulate the authentication process, potentially bypassing mechanisms designed to protect sensitive user data or session tokens.
The operational impact of this flaw is significant because it undermines the security model established during the client configuration phase. When a client is configured with only the authorization code grant type, it implies that the application relies on exchanging an authorization code for access and ID tokens using its secret key. This flow ensures that sensitive tokens are not exposed in browser URL fragments or local storage where they could be intercepted via cross-site scripting attacks. However, due to this vulnerability, if a malicious actor can influence the redirect_uri parameter during the initial authorization request, they may trick pretix into returning an ID token directly in the fragment of the callback URL instead of issuing an authorization code. This behavior effectively downgrades the security posture from a confidential client flow to one suitable only for public clients or implicit flows that are inherently more vulnerable to token leakage.
Exploitation of this vulnerability requires specific conditions, primarily the ability to execute JavaScript on a page controlled by the attacker but listed in the allowed redirect_uris for the target SSO client. This requirement aligns with typical cross-site scripting attack vectors where an attacker injects malicious scripts into a trusted web application's context. Once the script executes within the browser of a victim who is authenticated or being authenticated via pretix, it can intercept the ID token returned in the URL fragment. The attacker then exfiltrates this token to their own server, gaining unauthorized access to the user’s account without needing the client secret that would otherwise be required for an authorization code exchange. This scenario highlights the danger of allowing dynamic redirect URIs or insufficient validation of callback endpoints when combined with lax parameter checking on the identity provider side.
From a standards perspective, this issue maps directly to CWE-20 Improper Input Validation and CWE-345 Insufficient Verification of Data Authenticity within the context of OAuth 2.0 flows. It also relates to ATT&CK technique T1078 Valid Accounts, as it facilitates unauthorized access by stealing valid session credentials or tokens. Furthermore, the reliance on redirect_uri manipulation touches upon aspects of T1566 Phishing and potentially T1059 Command and Scripting Interpreter if the JavaScript execution is part of a broader injection attack. The failure to enforce strict response_type validation violates best practices outlined in RFC 6749 and OpenID Connect Core specifications, which mandate that authorization servers must reject requests with unsupported or mismatched parameters to prevent protocol abuse.
Mitigation strategies should focus on implementing rigorous input validation at the identity provider level. Pretix administrators and developers must ensure that every incoming authorization request explicitly checks whether the requested response_type is permitted for the specific client_id being used in the request. If a client is configured exclusively for code-based flows, any attempt to request an id_token or token response type should be immediately rejected with an appropriate error message such as invalid_request or unsupported_response_type. Additionally, organizations relying on this integration should audit their redirect_uri configurations to ensure that only trusted and strictly controlled domains are permitted. Implementing Content Security Policy headers can also help mitigate the impact of any potential cross-site scripting vulnerabilities by restricting where JavaScript can execute and preventing unauthorized data exfiltration from browser contexts. Regular security audits and penetration testing focused on OAuth flows are recommended to identify similar misconfigurations in identity provider implementations.