Executive brief
FOSSBilling is an open-source platform used by businesses to manage client billing and support. A security flaw allows an administrator to embed malicious code into emails sent to customers. When a customer views their email history in the client portal, this code could execute in their browser, potentially allowing the attacker to steal session information or perform unauthorized actions on the customer's behalf.
Technical details
A stored cross-site scripting (XSS) vulnerability exists in FOSSBilling's email history modules (mod_email_index.html.twig and mod_email_email.html.twig). The root cause is the use of the Twig '|raw' filter when rendering 'content_html' inside a JavaScript template literal for an iframe's 'srcdoc' attribute, which bypasses output escaping. An attacker with administrative access can inject payloads using backticks, template expressions (${...}), or script tags to break out of the JavaScript context. Successful exploitation allows for session cookie theft, CSRF token disclosure, or unauthorized actions in the context of the victim client. The issue is resolved in version 0.8.0.
Affected products
- FOSSBilling FOSSBilling >= 0.6.0, <= 0.7.2
Timeline
- 2026-06-12: advisory: GitHub Security Advisory published
- 2026-07-06: disclosed: CVE published to NVD
- 2026-08-01: patched: Fixed in version 0.8.0