#124513 - Guard Base64Url.DecodeFromChars against non-ASCII input#124540
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tannergooding merged 6 commits intodotnet:mainfrom Feb 19, 2026
Merged
#124513 - Guard Base64Url.DecodeFromChars against non-ASCII input#124540tannergooding merged 6 commits intodotnet:mainfrom
tannergooding merged 6 commits intodotnet:mainfrom
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dotnet#124513 - Guard Base64Url.DecodeFromChars against non-ASCII input Base64Url.DecodeFromChars in Microsoft.Bcl.Memory has an out-of-bounds read bug: DecodeFrom uses Unsafe.Add with raw char values as indices into a 256-element DecodingMap without checking the DecodeRemaining return value first. Non-ASCII chars (value > ~2048) cause an AccessViolationException on .NET 8. Workaround: Add System.Text.Ascii.IsValid check before decoding to reject non-ASCII input early. Base64/Base64Url only uses ASCII characters, so any non-ASCII input is inherently invalid. See: dotnet#124513
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This was referenced Feb 18, 2026
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...libraries/System.Private.CoreLib/src/System/Buffers/Text/Base64Helper/Base64DecoderHelper.cs
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jeffhandley
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Feb 19, 2026
src/libraries/System.Memory/tests/Base64Url/Base64UrlUnicodeAPIsUnitTests.cs
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LGTM. We can investigate the BOM issue afterward.
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/ba-g Unrelated networking failures on Android only |
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Base64Url.DecodeFromChars in Microsoft.Bcl.Memory has an out-of-bounds read bug: DecodeFrom uses Unsafe.Add with raw char values as indices into a 256-element DecodingMap without checking the DecodeRemaining return value first. Non-ASCII chars (value > ~2048) cause an AccessViolationException on .NET 8.
Workaround: Add System.Text.Ascii.IsValid check before decoding to reject non-ASCII input early. Base64/Base64Url only uses ASCII characters, so any non-ASCII input is inherently invalid.
Fixes #124513