CVE-2018-12495 in Discount
Summary
by MITRE
The quoteblock function in markdown.c in libmarkdown.a in DISCOUNT 2.2.3a allows remote attackers to cause a denial of service (heap-based buffer over-read) via a crafted file.
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Analysis
by VulDB Data Team • 03/27/2023
The vulnerability identified as CVE-2018-12495 resides within the DISCOUNT markdown processor library version 2.2.3a, specifically within the quoteblock function located in markdown.c. This flaw represents a heap-based buffer over-read condition that can be exploited by remote attackers through the careful crafting of input files. The DISCOUNT library serves as a widely-used markdown processing component that converts markdown formatted text into HTML output, making it a critical dependency for numerous web applications and content management systems.
The technical implementation of this vulnerability stems from inadequate bounds checking within the quoteblock processing logic. When the markdown parser encounters specific malformed input patterns, particularly those involving nested or improperly structured quote blocks, the buffer over-read occurs during memory access operations. This flaw manifests as the parser attempting to read memory locations beyond the allocated buffer boundaries, potentially leading to information disclosure or system instability. The vulnerability classifies as a CWE-125: Out-of-bounds Read according to the Common Weakness Enumeration catalog, which specifically addresses situations where programs access memory beyond the intended buffer limits.
From an operational perspective, this vulnerability poses significant risks to systems relying on DISCOUNT for markdown processing, particularly web applications that accept user-generated content. Attackers can craft malicious markdown files that trigger the buffer over-read condition, potentially causing application crashes, denial of service conditions, or in some scenarios, information leakage from adjacent memory regions. The remote exploitation capability means that systems processing markdown content from untrusted sources become vulnerable without proper input validation or sanitization measures. This vulnerability aligns with ATT&CK technique T1203: Exploitation for Client Execution, as it enables attackers to disrupt service availability through crafted input processing.
The impact of this vulnerability extends beyond simple service disruption, as it can potentially expose sensitive memory contents to attackers who understand the memory layout of affected systems. Systems running vulnerable versions of DISCOUNT may experience unpredictable behavior, including application crashes, memory corruption, or even potential privilege escalation in scenarios where the affected applications have elevated permissions. Organizations using this library in production environments should immediately assess their exposure and implement appropriate mitigations. The recommended approach includes upgrading to patched versions of DISCOUNT, implementing strict input validation for markdown content, and employing sandboxing techniques to isolate markdown processing operations from critical system components. Additionally, organizations should consider implementing automated scanning tools to identify and remediate vulnerable installations within their infrastructure.