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

> Attackers with admin access can configure malicious redirect targets, causing users to be silently redirected to external phishing sites via cached 301 responses.

- **Severity:** Medium 4.8 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 3 Jun 2026
- **Updated:** 4 Jun 2026
- **Also known as:** GHSA-v8rf-g37v-vgpx

## What is CVE-2026-43924?

CVE-2026-43924 is a medium-severity vulnerability in FOSSBilling, published on 3 Jun 2026. An attacker needs administrator access to exploit it, and only if a user opens a file or follows a link.

### Official 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.

Weakness: CWE-601 (URL Redirection to Untrusted Site)

## Which versions are affected by CVE-2026-43924?


## How do I fix CVE-2026-43924?

No fix has been published for CVE-2026-43924 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-43924 being exploited?

There is no known exploitation of CVE-2026-43924 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-43924 and fix it if it is affected.

What it is: CVE-2026-43924 is a medium-severity vulnerability in FOSSBilling, published on 3 Jun 2026. An attacker needs administrator access to exploit it, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-43924 in the wild and no public exploit code.

Affected product: FOSSBilling. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-43924/ (Markdown: https://insights.sbomify.com/CVE-2026-43924/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-43924
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-43924
- OSV: https://osv.dev/vulnerability/CVE-2026-43924

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-43924/
Summaries are generated and may contain mistakes; the official description above is the record.