Fix UTF-8 validation to reject invalid code points - #91
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Replace unsafe char::from_u32_unchecked with safe char::from_u32 to properly validate Unicode scalar values. This prevents undefined behavior from invalid characters created from: - Surrogate code points (U+D800..U+DFFF) - Code points above maximum Unicode (>U+10FFFF) - Overlong UTF-8 encodings Added validation checks for minimum encoding lengths to reject overlong sequences. Added tests to verify rejection of all invalid cases. Fixes a soundness issue where invalid UTF-8 byte sequences could create invalid char values, leading to undefined behavior.
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Jun 8, 2026
New * Added `RestrictedString::take_opt_from`. ([#90]) Improvements * `BIT_STRING` parsing now checks that the unused bits are zero in CER and DER modes. ([#97]) Bug fixes * Fixed `Utf8String` potentially accepting invalid UTF-8. ([#91] by [@sumleo]) * Fixed a panic in `Unsigned::from_bytes` when the input is all zero. ([#92] by [@sumleo]) * Fixed incorrect bounds check in `BitString::bit`. ([#93] by [@sumleo]) * Added character set validation to `FromStr` impl for `NumericString`, `PrintableString`, and `Ia5String`. ([#95] by [@sumleo])
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Summary
Fixes a soundness issue in UTF-8 string validation that could create invalid
charvalues from malformed UTF-8 sequences, leading to undefined behavior.Problem
The
Utf8CharSet::next_charimplementation usedchar::from_u32_uncheckedwithout proper validation, accepting:This violated Rust safety guarantees and could cause memory corruption or process termination.
Solution
unsafe char::from_u32_uncheckedwith safechar::from_u32char::from_u32inherently rejects surrogates and out-of-range valuesTesting
Added three test cases verifying rejection of:
All existing tests continue to pass.
Impact
This is a critical security fix that prevents undefined behavior from untrusted input (e.g., X.509 certificates with UTF8String fields).