CVE-2021-4249 in xml-conduit
Summary
by MITRE • 12/18/2022
A vulnerability was found in xml-conduit. It has been classified as problematic. Affected is an unknown function of the file xml-conduit/src/Text/XML/Stream/Parse.hs of the component DOCTYPE Entity Expansion Handler. The manipulation leads to infinite loop. It is possible to launch the attack remotely. Upgrading to version 1.9.1.0 is able to address this issue. The name of the patch is 4be1021791dcdee8b164d239433a2043dc0939ea. It is recommended to upgrade the affected component. The identifier of this vulnerability is VDB-216204.
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Analysis
by VulDB Data Team • 01/15/2023
The vulnerability identified as CVE-2021-4249 represents a critical security flaw within the xml-conduit library, specifically affecting the DOCTYPE entity expansion handler functionality. This issue resides in the Text/XML/Stream/Parse.hs file where an improper handling of XML parsing operations creates a condition that can lead to indefinite looping behavior. The vulnerability stems from the library's inability to properly terminate parsing operations when encountering certain malformed XML constructs, particularly those involving entity expansions within DOCTYPE declarations. The flaw manifests as an infinite loop during XML processing, which can consume excessive system resources and potentially lead to denial of service conditions.
The technical implementation of this vulnerability occurs when the xml-conduit library processes XML documents containing maliciously crafted DOCTYPE declarations that reference entities in ways that trigger recursive expansion patterns. The parsing logic fails to implement adequate safeguards against excessive entity expansion or recursion depth limits, allowing an attacker to craft XML payloads that cause the parser to enter an infinite loop. This condition can be triggered through remote exploitation when the library processes untrusted XML input from external sources, making it particularly dangerous in web applications and services that accept XML data from users or external systems.
From an operational perspective, this vulnerability poses significant risks to systems relying on xml-conduit for XML processing, particularly in environments where the library handles untrusted input from external sources. The infinite loop condition can lead to complete system resource exhaustion, application crashes, or service unavailability, effectively creating a denial of service scenario. Attackers can exploit this vulnerability by sending specially crafted XML documents that trigger the entity expansion handler, causing the application to consume excessive CPU cycles and memory resources. The remote exploitability aspect means that this vulnerability can be leveraged from external networks without requiring local system access, making it particularly dangerous for web-facing applications.
The mitigation strategy for CVE-2021-4249 centers on upgrading to version 1.9.1.0 of the xml-conduit library, which incorporates the patch identified by the commit hash 4be1021791dcdee8b164d239433a2043dc0939ea. This upgrade addresses the core issue by implementing proper bounds checking and recursion limits within the DOCTYPE entity expansion handler, preventing the infinite loop condition from occurring. Organizations should prioritize this upgrade across all systems that utilize the xml-conduit library, particularly in production environments where XML processing occurs with untrusted input. Additionally, implementing proper input validation and XML schema validation can provide additional defense-in-depth measures against similar vulnerabilities in other XML processing components.
This vulnerability aligns with CWE-835, which specifically addresses the issue of infinite loops in software applications, and can be categorized under ATT&CK technique T1499.004 for denial of service attacks. The flaw demonstrates the importance of implementing proper resource management and input validation in XML processing libraries, as similar issues can occur in other XML parsers and processing libraries that fail to implement adequate safeguards against malformed input. Security teams should conduct comprehensive vulnerability assessments to identify all systems using affected versions of xml-conduit and ensure proper patch management procedures are in place to prevent exploitation of similar vulnerabilities in the future.