CVE-2026-69183

Summary

Monkeytype is a minimalistic and customizable typing test. In 26.26.0 and earlier, the backend rate-limit key generator in backend/src/middlewares/rate-limit.ts uses client-controlled cf-connecting-ip and x-forwarded-for headers before the trust-proxy-derived req.ip value. An unauthenticated attacker can rotate either header to create a new bucket for each request, bypassing rootRateLimiter, badAuthRateLimiter, getKey(), and the getKeyWithUid() fallback used by public endpoints. This permits repeated POST /users/forgotPasswordEmail and verificationEmail requests, mail bombing registered users, consuming Firebase or SMTP quota, evading brute-force protection, and enabling resource exhaustion. Exploitability of cf-connecting-ip depends on deployment topology, but x-forwarded-for and direct-to-origin paths remain affected when those values are not overwritten by a trusted proxy. No fixed version is available as of this review.

Affected Software

Weaknesses

• CWE-290: CWE-290: Authentication Bypass by Spoofing
• CWE-307: CWE-307: Improper Restriction of Excessive Authentication Attempts
• CWE-644: CWE-644: Improper Neutralization of HTTP Headers for Scripting Syntax

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: poc
  • Automatable: no
  • Technical Impact: partial

Additional References

• https://github.com/monkeytypegame/monkeytype/security/advisories/GHSA-c878-p3jh-mmjf

References

• https://github.com/monkeytypegame/monkeytype/security/advisories/GHSA-c878-p3jh-mmjf

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