EUVD-2026-34176Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:P/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Primary rating from GitHub Advisory · only source for this CVE.
CVSS VectorGitHub Advisory
CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:P/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Lifecycle Timeline
3DescriptionGitHub Advisory
FOSSBilling is a free, open-source billing and client management system. Prior to version 0.8.0, the Redirect module does not validate the URL scheme of administrator-configured destination URLs before storing or issuing redirects. This allows arbitrary external URLs to be configured as redirect targets, creating an open redirect vulnerability exploitable for phishing attacks. Users following a legitimate FOSSBilling URL can be silently redirected to an attacker-controlled external site. The redirect is issued as a 301 (Moved Permanently) response, which browsers cache persistently, amplifying the impact. Exploitation requires administrator privileges to create or modify redirect entries, limiting practical attack scenarios to multi-admin environments or compromised admin accounts. Version 0.8.0 fixes the issue. Some workarounds are available. Restrict admin access to the Redirect module to trusted administrators only and/or audit existing redirect entries in the database (the extension_meta table with extension = 'mod_redirect') for any unexpected or external target URLs.
AnalysisAI
Open redirect vulnerability in FOSSBilling's Redirect module (prior to version 0.8.0) allows authenticated administrators to configure arbitrary external URLs as redirect targets without URL scheme validation. Users following a legitimate FOSSBilling link are silently issued a 301 Moved Permanently response to an attacker-controlled phishing site; because 301 responses are persistently cached by browsers, the redirect continues to function even after server-side correction until client caches expire. No public exploit identified at time of analysis; version 0.8.0 (released 2026-05-28) patches the issue.
Technical ContextAI
FOSSBilling is a PHP-based open-source billing and client management platform. The vulnerable component is mod_redirect, the built-in Redirect module, which stores administrator-configured destination URLs in the extension_meta database table (keyed by extension = 'mod_redirect') and issues those URLs directly as HTTP 301 responses without validating the URL scheme (e.g., permitting arbitrary http://, https://, or other scheme values pointing to external domains). CWE-601 (URL Redirection to Untrusted Site - Open Redirect) describes this root cause: user- or admin-supplied URLs are passed to the redirect response without allowlisting trusted schemes or enforcing same-origin or same-domain constraints. The choice of HTTP 301 rather than 302 is a significant technical amplifier - 301 is defined as a permanent redirect that browsers and intermediary caches store indefinitely, meaning clients who have already received the malicious redirect will continue to be sent to the attacker's site even after the server-side entry is corrected, until cache TTL expiry or explicit clearing. Version 0.8.0 addresses the issue by adding URL scheme validation prior to storage and issuance of redirects.
RemediationAI
Upgrade to FOSSBilling version 0.8.0, released 2026-05-28, which introduces URL scheme validation in the Redirect module before storing or issuing redirect responses. The release is available at https://github.com/FOSSBilling/FOSSBilling/releases/tag/0.8.0. Note that version 0.8.0 is a larger release with potentially breaking changes: it requires PHP 8.3 or newer, refactors guest API routes, removes the public system version endpoint, renames core classes (Box_Mod to FOSSBilling\Module), and migrates the frontend build system - operators maintaining custom modules, themes, or API integrations should review the full release notes and back up the installation before upgrading. If immediate upgrade is not feasible, restrict access to the Redirect module in the admin panel to the smallest set of fully trusted administrators (reducing the pool of accounts whose compromise could enable exploitation), and audit the extension_meta database table filtering on extension = 'mod_redirect' for unexpected or external destination URLs and remove any found. Be aware that 301 responses already cached by client browsers will persist beyond server-side correction - affected users may need to manually clear browser cache or be directed to do so following an incident. No additional network-level workarounds are effective since exploitation originates from an authenticated admin session.
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