YAML versions before 1.27_001 for Perl allow a loaded perl/glob document to replace any package…

Why it is Yellow

• CVSS 7.3 high
• Remotely exploitable without logging in

References

• https://github.com/ingydotnet/yaml-pm/commit/bace96b5e6661d521c7c515c94a09e081c911fce.patch
• https://github.com/ingydotnet/yaml-pm/issues/212
• https://metacpan.org/release/TINITA/YAML-1.28/changes
• http://www.openwall.com/lists/oss-security/2026/10/05/7

Original description

YAML versions before 1.27_001 for Perl allow a loaded perl/glob document to replace any package variable, which can lead to arbitrary code execution. A perl/glob document names a package and a symbol, and supplies the value assigned to it. Nothing restricts the name, so the target can be @INC or YAML's own load options. A perl/glob document that sets $YAML::LoadCode or $YAML::UseCode turns on code loading, which is off by default, for every later Load() in the process. A perl/code document is then passed to a string eval, so an attacker who supplies two documents to separate Load() calls in one process can execute arbitrary Perl code.