CVE-2026-13603

Summary

The payment integration pretix-oppwa provides support for the payment providers VR Payment, Hobex, and potentially others based on Oppwa's technology. The integration of Oppwa, following their official documentation, includes a step where the user is redirected from the payment provider back to our system with a query parameter like ?resourcePath=/v1/checkouts/{checkoutId}/payment in the URL. Our system is then supposed to fetch the status of the transaction from the URL given by baseUrl + resourcePath.

Our plugin pretix-oppwa did so insecurely by concatenating the parameter form the URL to the base domain of the API without further validation and, critically, without a / at the end of the baseUrl. Therefore, an attacker could inject a resourcePath argument in a way that causes pretix to call a different server instead. Since the request includes the access token (API key) of the Oppwa account, this would leak the access token, giving access to data contained in the payment provider's system. This is fixed with the release today by strictly validating the given API URL.

After installing the update, we recommend asking your payment provider for a new access token and updating it in pretix.

Affected Software

Weaknesses

• CWE-20: CWE-20 Improper input validation
• CWE-918: CWE-918 Server-Side request forgery (SSRF)

Workarounds

Workaround: If you are unable to update pretix quickly, we still recommend to try installing the pretix-oppwa plugin in the latest version. We have not tested it with every old pretix release, but we expect it to be compatible with any version after 2025.1. Otherwise, we recommend to uninstall the pretix-oppwa plugin.

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: none
  • Automatable: yes
  • Technical Impact: total

References

• https://pretix.eu/about/en/blog/20260701-release-2026-5-3/

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