CVE-2026-57533

Malicious HTML content could be injected into the email address of an order, which pretix showed without sanitization on the confirmation page for individual tickets in that order.

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. A client configured to only allow the `code` response type could receive back a valid token of another type, such as `id_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.

Some API endpoints allowed creating order payments referencing a gift card by using the auto-incremented internal ID. This ID was not checked and allowed creating payments that reference gift cards from different organizers and thereby obtaining their secret. The gift card is not charged in this case, but by then triggering a refund on the payment, one can increase the value of the gift card.

The mechanism binding files generated during a shredding process to the authentication method is not working correctly and the same session token is used for all token-based API users. This is similar to an issue fixed in 2026.7.1 but was missed while creating the fix. Since the files are referred to by randomly generated UUIDs and only exist for a day, there is virtually no risk, but it renders the added protection mechanism useless.

A chain of vulnerabilities was found in pretix: payment plugins (Stripe, Mollie, OPPWA, BitPay, Payone, SecuConnect, Sofort, Saferpay) do not validate session parameters beyond cryptographic signature, the redirect feature uses the same key and salt for signing as the plugins, and the admin impersonation feature allows changing user after injecting arbitrary parameters. An attacker with access to at least one event can become any backend user and access all data.

Pretix 2025 introduces a new API endpoint that returns check-in data for all events of an organizer instead of a specific event. This allows unauthorized users to access check-in information for other events.

Emails sent by pretix can utilize placeholders that will be filled with customer data. If the name of the attendee contained HTML or Markdown formatting, this was rendered as HTML in the resulting email, allowing a user to inject links or other formatted text through a maliciously formatted name. Since pretix applies a strict allow list approach to allowed HTML tags, this could not be abused for XSS, but it can be used to manipulate emails for phishing.