CVE-2024-37388 in lxml
Summary
by MITRE • 06/07/2024
An XML External Entity (XXE) vulnerability in the ebookmeta.get_metadata function of lxml before v4.9.1 allows attackers to access sensitive information or cause a Denial of Service (DoS) via crafted XML input.
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Analysis
by VulDB Data Team • 10/30/2024
The vulnerability identified as CVE-2024-37388 represents a critical XML External Entity (XXE) flaw within the ebookmeta.get_metadata function of the lxml library prior to version 4.9.1. This issue stems from inadequate input validation and processing of XML documents, creating a pathway for malicious actors to exploit the library's handling of external entity references. The vulnerability manifests when the library processes XML content that contains external entity declarations, allowing attackers to craft malicious payloads that can trigger unintended behavior during metadata extraction operations. The flaw is particularly concerning because lxml is widely used across various applications for XML processing, making this vulnerability potentially impactful across a broad range of systems and services.
The technical implementation of this XXE vulnerability occurs within the ebookmeta.get_metadata function where the library fails to properly sanitize XML input before processing. When malicious XML contains external entity references such as DOCTYPE declarations with external subsets or parameter entities, the lxml library may attempt to resolve these references during parsing. This behavior can result in information disclosure when the library retrieves and processes data from external resources, or it can cause denial of service conditions when crafted payloads trigger resource exhaustion or infinite loops during entity resolution. The vulnerability is classified as CWE-611 (Improper Restriction of XML External Entity Reference) and aligns with ATT&CK technique T1213.002 (Data from Information Repositories) as it enables unauthorized access to system resources through malformed XML processing.
The operational impact of CVE-2024-37388 extends beyond simple information disclosure, as it can be leveraged to create persistent denial of service conditions that affect application availability. Attackers can construct XML payloads that cause the library to consume excessive system resources or enter infinite processing loops, effectively rendering affected applications unavailable to legitimate users. Additionally, the vulnerability enables attackers to access internal system resources that should normally be protected from external access, potentially allowing them to read local files, perform port scans, or access network services that are typically isolated from external networks. This makes the vulnerability particularly dangerous in environments where applications process untrusted XML content from users or external sources.
Mitigation strategies for CVE-2024-37388 should prioritize updating the lxml library to version 4.9.1 or later, which includes proper XML entity handling and validation. Organizations should implement strict input validation for all XML content processed by applications using lxml, particularly when dealing with user-supplied or external data. Security measures should include disabling external entity resolution entirely within XML parsers, implementing proper XML schema validation, and employing network segmentation to limit potential attack vectors. Additional defensive measures include monitoring for unusual XML processing patterns, implementing web application firewalls to detect and block malicious XML payloads, and conducting regular security assessments of applications that utilize the vulnerable library. The vulnerability demonstrates the importance of maintaining up-to-date dependencies and implementing proper input sanitization practices to prevent XML-related security issues that can compromise both confidentiality and availability of systems.