CVE-2026-4177 in YAML::Syck
Summary
by MITRE • 03/17/2026
YAML::Syck versions through 1.36 for Perl has several potential security vulnerabilities including a high-severity heap buffer overflow in the YAML emitter.
The heap overflow occurs when class names exceed the initial 512-byte allocation.
The base64 decoder could read past the buffer end on trailing newlines.
strtok mutated n->type_id in place, corrupting shared node data.
A memory leak occurred in syck_hdlr_add_anchor when a node already had an anchor. The incoming anchor string 'a' was leaked on early return.
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Analysis
by VulDB Data Team • 03/22/2026
The YAML::Syck library for Perl presents a critical security vulnerability through CVE-2026-4177 that manifests across multiple memory corruption vectors within the YAML emitter component. This vulnerability affects versions through 1.36 and represents a significant threat to systems processing untrusted YAML input. The heap buffer overflow occurs when class names exceed the initial 512-byte allocation, creating a potential attack surface for remote code execution or denial of service scenarios. This flaw directly maps to CWE-122 Heap-based Buffer Overflow, which is categorized under the broader CWE-119 category of memory safety issues. The vulnerability demonstrates the classic pattern of insufficient bounds checking where the system fails to validate input size against allocated memory boundaries.
The base64 decoder component contains a separate but equally dangerous flaw where trailing newlines cause the decoder to read past the buffer end, leading to memory corruption. This type of vulnerability falls under CWE-125 Out-of-bounds Read, which can result in information disclosure or system instability when malformed input is processed. The strtok function presents another vector of compromise by mutating n->type_id in place, which corrupts shared node data structures and creates a potential for data tampering or information leakage. This corruption mechanism aligns with CWE-787 Out-of-bounds Write, as the function modifies memory locations outside the intended boundaries of the data structure. These memory corruption vulnerabilities collectively create an environment where an attacker can manipulate the parser's internal state and potentially execute arbitrary code.
The memory leak in syck_hdlr_add_anchor represents a persistent security weakness that can lead to resource exhaustion over time. When a node already possesses an anchor, the function fails to properly handle the incoming anchor string 'a' during early return conditions, causing memory to be leaked without proper cleanup. This memory leak directly corresponds to CWE-401 Memory Leak, which can result in gradual system degradation and potential denial of service attacks. The combination of these vulnerabilities creates a comprehensive attack surface that can be exploited through various attack vectors including remote code execution, information disclosure, and system instability. The attack patterns associated with these flaws align with ATT&CK techniques such as T1059 Command and Scripting Interpreter and T1106 Execution of File and Directory Permissions, as the vulnerabilities can be leveraged to execute malicious code within the target environment.
Organizations utilizing YAML::Syck in their Perl applications must implement immediate mitigations including upgrading to patched versions, implementing input validation controls, and deploying runtime protections. The remediation strategy should focus on addressing the heap overflow through proper buffer size validation, implementing bounds checking in the base64 decoder, and ensuring proper memory management in anchor handling functions. System administrators should consider deploying intrusion detection systems to monitor for exploitation attempts and establish monitoring procedures for unusual memory allocation patterns. The vulnerabilities described here represent a fundamental breakdown in memory safety controls that can be exploited through carefully crafted YAML input, making comprehensive system hardening essential for protecting against potential compromise.