CVE-2018-18385 in Asciidoctor
Summary
by MITRE
Asciidoctor v1.5.7.1 allows remote attackers to cause a denial of service (infinite loop), as demonstrated by web applications that deliver untrusted input to this product, because Parser#next_block misuses a "while true" statement.
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Analysis
by VulDB Data Team • 05/25/2023
The vulnerability identified as CVE-2018-18385 affects Asciidoctor version 1.5.7.1 and represents a critical denial of service flaw that can be exploited by remote attackers through untrusted input processing. This vulnerability exists within the parser component of the Asciidoctor library, specifically within the Parser#next_block method where a "while true" statement is misused, creating an infinite loop condition that can be triggered by maliciously crafted input. The flaw demonstrates a classic software engineering error where an infinite loop construct is improperly implemented, allowing attackers to consume system resources indefinitely. The vulnerability is particularly dangerous because it can be exploited through web applications that process user-provided content, making it a significant concern for any system that relies on Asciidoctor for document processing or rendering. The issue stems from the parser's inability to properly handle malformed or specially crafted input sequences that cause the loop to never terminate, resulting in resource exhaustion and service unavailability.
The technical implementation of this vulnerability involves the misuse of a while true loop construct within the Parser#next_block method, which creates an infinite execution path when processing certain input patterns. This type of flaw falls under CWE-835, which specifically addresses the issue of infinite loops in software implementations, and represents a form of resource exhaustion attack that can be classified under the ATT&CK technique T1499.100 - Network Denial of Service. The infinite loop occurs because the parser's state management logic fails to properly advance or terminate the loop condition when encountering specific input sequences, causing the application to hang indefinitely. The vulnerability is particularly insidious because it can be triggered through seemingly benign input that, when processed by the Asciidoctor parser, causes the execution to enter an endless cycle. The attack vector is typically through web applications that accept user input and process it through the Asciidoctor library, making it a common attack surface in content management systems, documentation generators, and web-based editors that utilize this library for rendering.
The operational impact of this vulnerability extends beyond simple service disruption to potentially affect system availability and resource allocation across multiple application layers. When exploited, the infinite loop consumes CPU resources continuously, potentially leading to system instability, application crashes, or complete service unavailability for legitimate users. The vulnerability affects any web application that processes untrusted input through Asciidoctor's parser component, including but not limited to documentation platforms, content management systems, and web-based editors that support asciidoc format processing. Organizations using vulnerable versions of Asciidoctor may experience cascading failures if multiple concurrent requests trigger the infinite loop, leading to denial of service conditions that can impact entire application stacks. The resource consumption pattern of this vulnerability can be particularly problematic in cloud environments or containerized applications where CPU limits are enforced, as the infinite loop can quickly exhaust allocated resources and trigger automatic scaling mechanisms or resource throttling.
Mitigation strategies for CVE-2018-18385 should focus on immediate version upgrades to Asciidoctor 1.5.8 or later, which contain the patched parser implementation that resolves the infinite loop condition. System administrators should implement input validation and sanitization measures to reduce the attack surface, particularly for applications that process user-provided content through Asciidoctor. Additionally, implementing rate limiting and resource monitoring can help detect and prevent exploitation attempts, while application-level timeouts should be configured to prevent indefinite processing of input sequences. The fix for this vulnerability demonstrates the importance of proper loop termination conditions in parser implementations and emphasizes the need for comprehensive testing of edge cases in input processing components. Organizations should also consider implementing network-level controls and intrusion detection systems to monitor for patterns associated with this vulnerability, particularly in web applications that process untrusted content through Asciidoctor or similar parsing libraries. Regular security audits and dependency updates should be prioritized to prevent similar issues in other components of the application stack that may be susceptible to similar infinite loop vulnerabilities.