YAML::Syck versions before 1.38 for Perl has an out-of-bounds read.

The base60 (sexagesimal) parsing code in perl_syck.h has a buffer underflow bug in both int#base60 and float#base60 handlers. When processing the leftmost segment of a colon-separated value (e.g., the 1 in 1:30:45), the inner while loop can decrement a pointer past the start of the string buffer:

while ( colon >= ptr && *colon != ':' )
{
    colon--;
}
if ( *colon == ':' ) *colon = '\0';  // colon may be ptr-1 here

When no colon is found (final/leftmost segment), colon becomes ptr-1, and the subsequent *colon dereference reads one byte before the allocated buffer.

References

• https://nvd.nist.gov/vuln/detail/CVE-2026-5089
• cpan-authors/YAML-Syck#132
• cpan-authors/YAML-Syck#133
• https://github.com/cpan-authors/YAML-Syck/commit/208a4d3bd1b5cdb4a791a6e3905bd6bd45e9d005.patch
• https://metacpan.org/release/TODDR/YAML-Syck-1.38/changes
• http://www.openwall.com/lists/oss-security/2026/05/12/16