Quantum Secular Labs / Blog / Advisories

CVE-2017-20285: YAML versions before 1.30 for Perl allow a loaded document to trigger the DESTROY method of arbitrary classes.

CVE-2017-20285 is rated critical with a CVSS v3.1 base score of 9.1. Per its scoring, it can be exploited over the network, without authentication, without any user interaction.

Vulnerability description

YAML versions before 1.30 for Perl allow a loaded document to trigger the DESTROY method of arbitrary classes. A perl/hash:Class tag blesses a hash into the class it names. The document supplies the object's fields, and Perl calls DESTROY when it goes out of scope. What DESTROY does depends on the classes the process has loaded. With File::Temp::Dir from core Perl, it can delete a directory tree the document names.

Severity breakdown

CVSS v3.1 9.1: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Attack vector: Network. Exploitable remotely over the network, with no need for local or physical access.
Attack complexity: Low. No special conditions; the attack can be repeated reliably.
Privileges required: None. No account or prior access is needed.
User interaction: None. No action from any user is needed.
Scope: Unchanged. Impact stays within the vulnerable component.
Confidentiality impact: High. Total loss of confidentiality; sensitive data can be fully disclosed.
Integrity impact: High. Total loss of integrity; data or system state can be fully modified.
Availability impact: None. No effect on availability.

Underlying weakness

CWE-470: Use of Externally-Controlled Input to Select Classes or Code

The product uses external input with reflection to select which classes or code to use, but it does not sufficiently prevent the input from selecting improper classes or code.

CWE-502: Deserialization of Untrusted Data

The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.