Impact The two parsers resolved duplicates inconsistently and silently: - "Content.disposition()" retained the last occurrence of each parameter. - "Content.type()" retained the first occurrence of charset and boundary. Either behavior creates a parameter-smuggling primitive when another component in the request-processing chain (a WAF, reverse proxy, security filter, or alternate parser) resolves duplicates the opposite way. The primary attack vector is upload filename allowlist bypass: "Content-Disposition: form-data; name="file"; filename="safe.txt"; filename="shell.php"" Patches The issue has been patched in 6.0.2. Workarounds Pre or post validate headers looking for duplicates. Resources - "RFC 6266 §4.1 — Content-Disposition syntax" (https://www.rfc-editor.org/rfc/rfc6266#section-4.1) - "RFC 7231 §3.1.1.1 — Content-Type syntax" (https://www.rfc-editor.org/rfc/rfc7231#section-3.1.1.1) - "RFC 7230 §3.2.6 — token character set" (https://www.rfc-editor.org/rfc/rfc7230#section-3.2.6)