YAML::Syck versions through 1.36 for Perl has several potential security vulnerabilities including a high-severity heap buffer overflow in the YAML emitter.

The heap overflow occurs when class names exceed the initial 512-byte allocation.

The base64 decoder could read past the buffer end on trailing newlines.

strtok mutated n->typeid in place, corrupting shared node data.

A memory leak occurred in syckhdlraddanchor when a node already had an anchor. The incoming anchor string 'a' was leaked on early return.

XML::Parser versions through 2.47 for Perl has an off-by-one heap buffer overflow in stserialstack

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, parsestream() 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.

YAML::Syck versions before 1.36 for Perl has missing null-terminators which causes out-of-bounds read and potential information disclosure

Missing null terminators in token.c leads to but-of-bounds read which allows adjacent variable to be read

The issue is seen with complex YAML files with a hash of all keys and empty values.  There is no indication that the issue leads to accessing memory outside that allocated to the module.