CVE-2026-13602

We found a chain of combining multiple weaknesses in the product that could allow an attacker to become any user in the backend and access any data:

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The payment integration plugins Stripe (included in the core system), pretix-mollie, pretix-oppwa, pretix-bitpay, pretix-payone, pretix-secuconnect, pretix-sofort, and pretix-saferpay

contain a code path that is intended for the transport of session

parameters from a tab with isolated cookies (e.g. in the pretix widget)

to a new tab. For this purpose, a set of session parameters is

cryptographically signed and then passed to the new tab as a URL

parameter. The plugins perform no further validation of the session

parameters, other than the cryptographic signature being valid. This is

fixed with the releases issued today by strictly validating that no

session parameters outside of the scope of the respective plugin may be

set.

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An unrelated feature in the core system is used to generate redirect links that obfuscate any Referer

headers for outgoing links to prevent leakage of secrets in URLs. This

redirect page also requires cryptographically signed parameters.

Unfortunately, it uses the same key and salt for the signature as the

previously mentioned feature in the payment integration plugins. A

motivated attacker with access to at least one event in the backend can

trick the system into cryptographically signing arbitrary content using

specially crafted links. In combination with the previous issue, the

attacker could use this to set and modify arbitrary parameters on their

user session by injecting the signed parameters into the feature of the

payment providers. This is fixed with the releases issued today by using

different salts for the signature for each plugin and feature.

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A third, unrelated feature in the core system is used for admin users

to act on behalf of another user, mostly for debugging purposes. With

being able to insert arbitrary parameters into a session, an attacker

can abuse this feature to change their session from their actual user to

any user in the system by guessing a valid user ID. This is fixed with

the release today by requiring unguessable information to be contained

in the session of the user to switch to.