CVE-2017-18640 in PeopleSoft Enterprise PT PeopleTools
Summary
by MITRE
The Alias feature in SnakeYAML 1.18 allows entity expansion during a load operation, a related issue to CVE-2003-1564.
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Analysis
by VulDB Data Team • 01/11/2026
The vulnerability identified as CVE-2017-18640 resides within the SnakeYAML library version 1.18, specifically affecting its Alias feature implementation. This flaw represents a significant security concern as it enables entity expansion during YAML loading operations, creating a pathway for malicious actors to exploit the system through carefully crafted input data. The vulnerability is particularly concerning because it mirrors the characteristics of CVE-2003-1564, which established a precedent for XML external entity processing issues that have long been recognized as critical attack vectors in data parsing libraries.
The technical flaw manifests when the SnakeYAML library processes YAML documents containing aliases that reference entities within the document structure. During the load operation, the library fails to properly validate or restrict the expansion of these aliases, allowing attackers to construct malicious YAML content that can trigger excessive resource consumption or unintended behavior. This occurs because the alias resolution mechanism does not adequately enforce boundaries on entity expansion, potentially leading to recursive expansion patterns that can exhaust system resources or cause denial of service conditions. The vulnerability operates at the parsing layer where YAML documents are interpreted and converted into in-memory data structures, making it particularly dangerous as it can affect any application relying on SnakeYAML for configuration management or data processing.
The operational impact of CVE-2017-18640 extends beyond simple denial of service scenarios to encompass potential information disclosure and system compromise. When exploited, this vulnerability can cause applications to consume excessive memory or processing power, leading to service disruption and potentially enabling attackers to perform resource exhaustion attacks against systems. The vulnerability is particularly dangerous in environments where SnakeYAML is used to process untrusted input from external sources, such as user-provided configuration files, API payloads, or data import operations. Attackers can craft YAML documents that, when processed by vulnerable applications, trigger cascading alias expansions that consume system resources in a manner that can be difficult to detect and mitigate. This type of vulnerability aligns with ATT&CK technique T1210, which describes exploitation of weaknesses in remote services, and falls under CWE-400, which covers unchecked resource consumption vulnerabilities.
Mitigation strategies for CVE-2017-18640 should focus on immediate library upgrades to versions that address the alias expansion vulnerability, typically SnakeYAML 1.23 or later. Organizations should implement input validation and sanitization measures to restrict YAML content that can be processed by applications using SnakeYAML, particularly when handling external or untrusted input. Additional protective measures include configuring resource limits and timeouts on YAML processing operations, implementing proper access controls to limit which entities can be referenced through aliases, and monitoring system behavior for unusual resource consumption patterns that might indicate exploitation attempts. Security teams should also consider implementing network segmentation and application-level firewalls to limit exposure to potential attackers who might attempt to exploit this vulnerability through various attack vectors including web applications, API endpoints, or configuration management systems that rely on SnakeYAML for data processing.