XML::Parser versions through 2.45 for Perl could overflow the pre-allocated buffer size cause a heap corruption (double free or corruption) and crashes. A :utf8 PerlIO layer, parse_stream() in Expat.xs could overflow the XML input buffer because Perl's read() returns decoded characters while SvPV() gives back multi-byte UTF-8 bytes that can exceed the pre-allocated buffer size. This can cause heap corruption (double free or corruption) and crashes.

• https://github.com/cpan-authors/XML-Parser/commit/56b0509dfc6b559cd7555ea81ee62e3622069255.patch
• https://github.com/cpan-authors/XML-Parser/issues/64
• https://metacpan.org/release/TODDR/XML-Parser-2.46/changes
• https://rt.cpan.org/Ticket/Display.html?id=19859
• http://www.openwall.com/lists/oss-security/2026/03/19/1
• http://www.openwall.com/lists/oss-security/2026/03/22/3

XML::Parser versions through 2.47 for Perl has an off-by-one heap buffer overflow in st_serial_stack. In the case (stackptr == stacksize - 1), the stack will NOT be expanded. Then the new value will be written at location (++stackptr), which equals stacksize and therefore falls just outside the allocated buffer. The bug can be observed when parsing an XML file with very deep element nesting

• https://github.com/cpan-authors/XML-Parser/commit/3eb9cc95420fa0c3f76947c4708962546bf27cfd.patch
• https://github.com/cpan-authors/XML-Parser/issues/39
• https://rt.cpan.org/Ticket/Display.html?id=19860
• http://www.openwall.com/lists/oss-security/2026/03/19/2