Reject overlong UTF-8 forms in _Mbrtowc and add test case - #6060
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Stephan T. Lavavej (StephanTLavavej) merged 5 commits intoFeb 11, 2026
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Added UTF-8 validation in _Mbrtowc to reject overlong encodings and out-of-range code points, returning EILSEQ instead of accepting ill-formed sequences.
Alex Guteniev (AlexGuteniev)
approved these changes
Jan 31, 2026
Stephan T. Lavavej (StephanTLavavej)
approved these changes
Jan 31, 2026
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Thank you so much for figuring out how to salvage this! 😻 Now I finally understand what the issue is. I pushed additional test coverage. |
Stephan T. Lavavej (StephanTLavavej)
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Stephan T. Lavavej (StephanTLavavej)
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I'm mirroring this to the MSVC-internal repo. Please notify me if any further changes are pushed, otherwise no action is required. |
Stephan T. Lavavej (StephanTLavavej)
merged commit Feb 11, 2026
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This PR adds test case on top of #5943, and removes the check for out-of-range code points.
While
_Mbrtowcis used by both<locale>and<format>facilities, only the former are affected because the<format>functions call the constexpr function_Decode_utfif the encoding is UTF-8.I removed the check for out-of-range values because I think
wchcan't exceed 0xFFFF: there's an early return if the result won't fit in the Basic Multilingual Plane,STL/stl/src/xmbtowc.cpp
Lines 110 to 115 in 3f76681