What’s Vulnerable › Vulnerabilities

CVE-2026-43924: FOSSBilling has an open redirect via administrator-configured redirect targets

• Severity: medium (CVSS 4.8 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-06-03 · updated 2026-07-22
• Weakness: CWE-601

Description

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.

Affected products

• FOSSBilling: before 0.8.0

References

• https://github.com/FOSSBilling/FOSSBilling/releases/tag/0.8.0
• https://github.com/FOSSBilling/FOSSBilling/security/advisories/GHSA-v8rf-g37v-vgpx

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