CVE-2018-11503 in Discount
Summary
by MITRE
The isfootnote 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, as demonstrated by mkd2html.
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Analysis
by VulDB Data Team • 03/17/2023
The vulnerability identified as CVE-2018-11503 resides within the DISCOUNT markdown processing library version 2.2.3a, specifically within the isfootnote 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 vulnerability manifests when the mkd2html utility processes malformed markdown documents, creating a scenario where the application attempts to read memory beyond the allocated buffer boundaries. This type of memory corruption vulnerability falls under the category of memory safety issues and can be classified as a CWE-125 vulnerability, which specifically addresses out-of-bounds read conditions.
The technical execution of this vulnerability occurs during the markdown parsing process where the isfootnote function fails to properly validate input data when processing footnote references within markdown documents. When a maliciously crafted file is processed, the function attempts to access memory locations that have not been properly allocated or are outside the intended buffer boundaries. This over-read condition can lead to unpredictable behavior including application crashes, data corruption, or potentially more severe consequences depending on the memory layout and execution context. The vulnerability is particularly concerning because it can be triggered remotely through file processing, making it applicable to web applications that accept user-uploaded markdown files for conversion or rendering.
The operational impact of CVE-2018-11503 extends beyond simple denial of service conditions, as it can disrupt the normal operation of any system that relies on the DISCOUNT library for markdown processing. Applications that utilize mkd2html or similar tools for converting markdown content to HTML are at risk of experiencing service interruptions when processing maliciously crafted files. This vulnerability is particularly relevant in web applications where user-generated content is processed, as attackers can upload specially crafted markdown files that will cause the application to crash or behave unpredictably. The potential for remote code execution cannot be entirely ruled out in some scenarios, though the primary impact remains denial of service. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique related to Network Denial of Service and could potentially enable further exploitation if combined with other vulnerabilities.
Mitigation strategies for this vulnerability should focus on immediate remediation through version updates to DISCOUNT library versions that contain fixes for the buffer over-read condition. System administrators should prioritize patching affected applications and updating the DISCOUNT library to versions that address the specific memory handling issues within the isfootnote function. Input validation and sanitization should be implemented at the application level to prevent processing of malformed markdown files, though this approach is secondary to the core library patching. Additionally, implementing proper memory error detection tools and runtime protections can help identify and prevent exploitation attempts. The vulnerability highlights the importance of regular security updates and proper input validation in preventing memory corruption exploits that can lead to system instability and potential security breaches. Organizations should also consider implementing network segmentation and monitoring to detect unusual processing patterns that might indicate exploitation attempts.