Fix GH-21734: WHATWG URL parser accepts overlong UTF-8 and invalid continuation bytes#35
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Fix GH-21734: WHATWG URL parser accepts overlong UTF-8 and invalid continuation bytes#35
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… continuation bytes lxb_encoding_decode_valid_utf_8_single() skipped all UTF-8 validation (continuation byte range, overlong sequences, surrogates), trusting the caller to pass valid input. The URL parser calls it on untrusted user input at 7 sites, and the IDNA code calls it on percent-decoded hostname bytes at 2 more. Overlong ASCII characters in hostnames passed through IDNA processing as their target codepoints, producing valid domains from byte sequences that look nothing like the canonical form (e.g., %C1%A5%C1%B6... → "evil.com"). Chrome, Firefox, and Safari reject these at the UTF-8 decode step. Add the missing validation to decode_valid_utf_8_single: - 2-byte: reject lead bytes < 0xC2 (overlong), validate continuation - 3-byte: validate continuations, reject 0xE0 + < 0xA0 (overlong), reject 0xED + > 0x9F (surrogates) - 4-byte: reject lead > 0xF4, validate continuations, reject 0xF0 + < 0x90 (overlong), reject 0xF4 + > 0x8F (> U+10FFFF) On error, advance by 1 byte (not the full sequence length) so the next byte gets its own decode attempt, matching browser behavior. Closes phpGH-21734
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Submitted upstream as php#21735 |
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Fixes php#21734.
lxb_encoding_decode_valid_utf_8_single()had no UTF-8 validation: no continuation byte range checks, no overlong sequence rejection, no surrogate rejection. It was written to assume the caller already verified the input. The URL parser calls it on untrusted user input at 7 sites, and the IDNA code calls it on percent-decoded hostname bytes at 2 more.An attacker feeding overlong ASCII characters into a hostname could get them through IDNA processing as their target codepoints, producing valid domains from byte sequences that look nothing like the canonical form.
%C1%A5%C1%B6%C1%A9%C1%AC.comresolved toevil.com. Chrome, Firefox, and Safari reject overlong sequences at the UTF-8 decode step.Added the missing validation to
decode_valid_utf_8_single:On error, the decoder advances by 1 byte (not the full sequence length) so the next byte gets its own decode attempt, matching browser behavior.