The YAML::Syck library for Perl contains a buffer underflow bug in the base60 parsing code used for both integer and float handlers. During parsing of colon-separated values, an inner loop can decrement a pointer past the beginning of the input string buffer for the leftmost segment, leading to a read one byte before the allocated memory. While the description does not explicitly state that the read can be used for data leakage, it is inferred that this out‑of‐bounds read could potentially expose adjacent memory contents, thereby creating a risk of information disclosure.

The vulnerability affects the TODDR YAML::Syck package on CPAN. Any installation of this library with a version prior to 1.38 is susceptible. Versions 1.38 and later include the fix, so updating to a current release restores safe operation. Any Perl application that deserializes YAML data and relies on this module can be impacted.

The CVSS score of 7.3 reflects a high severity for this out‑of‑bounds read. The EPSS score of <1% indicates a very low likelihood of exploitation in the near term. The flaw is not listed in CISA’s KEV catalog, meaning that no publicly documented exploits exist at this time. Potential exploitation would require an attacker to supply crafted YAML input that triggers the parsing of an incomplete colon‑separated value, which may be feasible in many untrusted data scenarios.