CVE-2019-25777

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

Published Oct 5, 2026 CVSS 3.1 · 7.3 High EPSS < 1% KEV · Not listed
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.

Remediation

Vendor Solution

Upgrade to YAML 1.28 or later.


Vendor Workaround

For deployments that cannot upgrade to YAML 1.28, set $YAML::LoadBlessed = 0 before loading untrusted input. The option exists from YAML 1.25 and gates glob loading too.

Tracking

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Advisories

Source ID Title
Ubuntu USN Ubuntu USN USN-8925-1 YAML-LibYAML vulnerabilities
History
Type Values Removed Values Added
First Time appeared Ingydotnet
Ingydotnet yaml
Vendors & Products Ingydotnet
Ingydotnet yaml
Type Values Removed Values Added
Metrics cvssV3_1

{'score': 8.1, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H'}

ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

cvssV3_1

{'score': 7.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L'}

Type Values Removed Values Added
References
Metrics threat_severity

None

cvssV3_1

{'score': 8.1, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H'}

threat_severity

Important

Type Values Removed Values Added
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.
Title 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
Weaknesses CWE-502
CWE-914
References
Weaknesses

Sources

Status
PUBLISHED
Assigner
CPANSec
Published
Updated
Oct 6, 2026, 4:58 PM
Reserved
Sep 21, 2026, 9:17 PM
Status
Deferred
Published
Oct 5, 2026, 7:16 AM
Modified
Oct 6, 2026, 5:17 PM
Severity
Important
Public date
Oct 5, 2026, 6:50 AM