CVE-2020-26148 in md4c
Summary
by MITRE • 10/04/2020
md_push_block_bytes in md4c.c in md4c 0.4.5 allows attackers to trigger use of uninitialized memory, and cause a denial of service (e.g., assertion failure) via a malformed Markdown document.
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Analysis
by VulDB Data Team • 11/15/2020
The vulnerability identified as CVE-2020-26148 resides within the md4c library version 0.4.5, specifically in the md_push_block_bytes function located in the md4c.c source file. This represents a critical security flaw that enables remote attackers to exploit uninitialized memory access patterns through carefully crafted malformed Markdown documents. The md4c library serves as a lightweight Markdown parser implementation widely used in various applications for processing Markdown formatted text, making this vulnerability particularly concerning for software systems that rely on proper Markdown parsing capabilities.
The technical flaw manifests when the md_push_block_bytes function processes malformed input data without proper validation or initialization checks. This function is responsible for handling block-level elements in Markdown documents and operates under the assumption that memory regions have been properly initialized before access. However, the vulnerability allows attackers to feed specially constructed Markdown content that causes the parser to reference uninitialized memory locations, leading to unpredictable behavior and system instability. The flaw falls under the category of uninitialized memory access as classified by CWE-457, which specifically addresses the use of uninitialized variables or memory regions in programming contexts.
The operational impact of this vulnerability extends beyond simple denial of service conditions, though that represents the primary consequence. When exploited, the vulnerability can trigger assertion failures within the md4c library, causing applications to crash or terminate unexpectedly. This makes the vulnerability particularly dangerous in production environments where continuous availability is critical, as attackers could potentially cause service disruptions by sending malicious Markdown content to applications that utilize md4c for document processing. The vulnerability can be leveraged in various attack scenarios including web applications, content management systems, and any software that accepts user-provided Markdown input for processing.
The exploitation of CVE-2020-26148 aligns with ATT&CK technique T1203, which covers the use of malformed input to trigger system instability and denial of service conditions. This vulnerability demonstrates how seemingly benign input processing functions can become attack vectors when proper memory management and input validation are not implemented. Organizations using md4c version 0.4.5 should consider this vulnerability as a potential entry point for broader attack campaigns targeting application availability. The vulnerability also intersects with ATT&CK technique T1068, which covers the exploitation of vulnerabilities in software components, making it relevant for threat hunting and incident response activities focused on identifying unauthorized access attempts through software flaws.
Mitigation strategies for this vulnerability should prioritize immediate remediation through version upgrades to md4c 0.4.6 or later, which contains the necessary patches to address the uninitialized memory access issue. Organizations should also implement input validation mechanisms that sanitize Markdown content before processing, even when using patched library versions. Additionally, deploying intrusion detection systems that monitor for malformed input patterns and implementing proper error handling that prevents crash conditions can help reduce the impact of potential exploitation attempts. The vulnerability serves as a reminder of the importance of thorough memory management practices and proper input validation in security-critical software components, particularly in parsing libraries that handle untrusted user input.