Summary Form and login CAPTCHA verification interpolate the user-supplied widget token unencoded into the server-side verification URL/body, allowing a crafted token to inject query parameters into the reCAPTCHA/hCaptcha verify request.
Details
- packages/form/lib/recaptcha.js:39 — recaptchaUri = 'https://www.google.com/recaptcha/api/siteverify?secret=${recaptchaSecret}&response=${input.recaptcha}'
- packages/login-recaptcha/index.js:44 — same pattern for login
- packages/login-hcaptcha/index.js:47 — body: 'response=${token}&secret=${secret}'
PoC
input.recaptcha = 'attacker_token&secret=INJECTED_SECRET&something=1' → resulting verify URL: https://www.google.com/recaptcha/api/siteverify?secret=&response=attacker_token&secret=INJECTED_SECRET&something=1 # (replicated exactly from recaptcha.js:39)
Impact Low: a crafted token smuggles extra key=value pairs (secret, extra response) into the outbound verify call, forcing verification failures (DoS of the captcha gate and of captcha-gated login/form flows) and enabling automated bypass probing; no secret exfiltration.
Remediation — Build the verify request with URL + searchParams (or encodeURIComponent on both secret and response), and validate the token against ^[A-Za-z0-9.-]{1,2048}$ before use.