PT-2026-33852 · Gnu C Library · Glibc
Rocket Ma
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Published
2026-04-20
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Updated
2026-04-20
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CVE-2026-5928
None
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Calling the ungetwc function on a FILE stream with wide characters encoded in a character set that has overlaps between its single byte and multi-byte character encodings, in the GNU C Library version 2.43 or earlier, may result in an attempt to read bytes before an allocated buffer, potentially resulting in unintentional disclosure of neighboring data in the heap, or a program crash.
A bug in the wide character pushback implementation ( IO wdefault pbackfail in libio/wgenops.c) causes ungetwc() to operate on the regular character buffer (fp-> IO read ptr) instead of the actual wide-stream read pointer (fp-> wide data-> IO read ptr). The program crash may happen in cases where fp-> IO read ptr is not initialized and hence points to NULL. The buffer under-read requires a special situation where the input character encoding is such that there are overlaps between single byte representations and multibyte representations in that encoding, resulting in spurious matches. The spurious match case is not possible in the standard Unicode character sets.
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Weakness Enumeration
Related Identifiers
Affected Products
Glibc