CVE-2026-101266 in Pretix
Summary
by MITRE • 09/29/2026
A logic flaw in the checkout flow allows users to bypass validations performed during the check-in by skipping entire check-in steps.
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Analysis
by VulDB Data Team • 09/29/2026
The identified vulnerability represents a critical logical error within the application's transactional workflow, specifically affecting the sequence of operations between user registration or account setup and final purchase completion. In secure software design, it is imperative that state transitions are strictly enforced to ensure data integrity and compliance with business rules. This flaw arises because the backend system fails to validate whether prerequisite steps, such as identity verification, address confirmation, or security questionnaire responses completed during a check-in phase, have actually been executed before allowing access to the checkout module. By manipulating client-side requests or exploiting an inconsistency in session state management, an attacker can bypass these mandatory intermediate stages entirely. This type of issue is classically categorized under CWE-840, which describes performing actions with insufficiently checked inputs, and more specifically relates to CWE-209 regarding the generation of error messages that contain sensitive information if the bypass reveals internal states, though primarily it falls under CWE-613 for Insufficient Session Expiration or improper state management in multi-step processes.
From a technical perspective, this vulnerability exploits the assumption that client-side validation is sufficient to enforce workflow integrity. Modern web applications often rely on JavaScript to guide users through sequential forms, creating an illusion of enforced progression. However, if the server does not independently verify the completion status of each step by checking database records or session tokens associated with specific check-in actions, it becomes trivial for a malicious actor to construct HTTP requests that skip directly to the checkout endpoint. The attacker might inject parameters indicating previous steps are complete without actually having performed them, or simply omit references to those steps if they are not strictly required in the request payload structure. This lack of server-side state validation allows the application to proceed with sensitive operations under false premises regarding user eligibility or data completeness.
The operational impact of this vulnerability is significant and varies depending on the nature of the check-in requirements. If the skipped steps involve age verification, identity authentication, or security clearance checks, bypassing them could lead to regulatory non-compliance, such as violations of GDPR, CCPA, or industry-specific standards like PCI-DSS for payment processing. In e-commerce contexts, skipping address validation might result in shipping errors and increased fraud rates, while bypassing terms acceptance could expose the organization to legal liabilities regarding user consent. Furthermore, if the check-in process includes security questions or two-factor authentication setups, allowing users to skip these steps compromises account security, potentially leading to unauthorized access or account takeover scenarios where critical security configurations are left at their default, insecure states.
To mitigate this vulnerability, developers must implement robust server-side validation for every step in a multi-stage workflow. The application should maintain an explicit state machine that tracks the completion status of each required action and refuses to transition to subsequent stages unless all prerequisites are met. This can be achieved by storing session-specific flags or database records that confirm the execution of check-in steps, which must be verified before processing checkout requests. Additionally, implementing idempotency keys for transactional operations ensures that even if a request is replayed or manipulated, the system maintains consistency. It is also recommended to utilize standardized frameworks and libraries that handle workflow state management securely, reducing the likelihood of manual implementation errors. Regular security testing, including penetration tests focused on business logic flaws, should be conducted to identify similar bypasses in other parts of the application lifecycle.