CVE-2018-11468 in Discount
Summary
by MITRE
The __mkd_trim_line function in mkdio.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, as demonstrated by mkd2html.
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Analysis
by VulDB Data Team • 03/17/2023
The vulnerability identified as CVE-2018-11468 resides within the DISCOUNT markdown processing library version 2.2.3a, specifically in the __mkd_trim_line function located in mkdio.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 markdown parser implementation that converts markdown text into HTML format, with mkd2html being one of its primary command-line utilities. When processing specially crafted markdown documents, the vulnerable function fails to properly validate input boundaries, leading to memory access violations that can result in application crashes or system instability.
The technical execution of this vulnerability involves the manipulation of markdown syntax elements that trigger the buffer over-read during the line trimming process. The __mkd_trim_line function appears to inadequately handle memory allocation and boundary checking when processing certain markdown constructs, particularly those involving inline formatting or complex nesting patterns. This flaw falls under the category of memory safety issues and aligns with CWE-125, which describes out-of-bounds read vulnerabilities. The vulnerability can be leveraged by attackers to cause denial of service conditions, where legitimate users or services relying on the DISCOUNT library may experience application termination or unexpected behavior when processing maliciously formatted markdown content.
From an operational perspective, this vulnerability presents significant risks to systems that process user-generated markdown content, particularly web applications, content management systems, and collaborative platforms that utilize markdown parsing. The remote exploitation capability means that attackers can trigger the vulnerability without requiring local access, making it particularly dangerous in multi-tenant environments or public-facing applications. The impact extends beyond simple service disruption to potentially compromise system availability, as applications may crash repeatedly when encountering malicious input, leading to denial of service for legitimate users. Security professionals should consider this vulnerability in the context of the ATT&CK framework under the T1499 category, which covers network denial of service attacks, and T1059 for command and scripting interpreter usage patterns that may be employed in exploitation.
Mitigation strategies for CVE-2018-11468 should prioritize the immediate upgrade of the DISCOUNT library to version 2.2.4 or later, where the buffer over-read issue has been resolved through proper input validation and memory boundary checking. Organizations should implement defensive programming practices such as input sanitization and validation for all markdown processing components, ensuring that boundary checks are performed before memory access operations. Additionally, deploying web application firewalls or content filters that can detect and block suspicious markdown patterns may provide additional protection layers. System administrators should also consider implementing monitoring and alerting mechanisms to detect unusual application behavior or crash patterns that may indicate exploitation attempts. The vulnerability highlights the importance of maintaining updated security libraries and the potential consequences of failing to address memory safety issues in widely used parsing libraries that handle untrusted input data from multiple sources.