CVE-2017-18258 in libxml2
Summary
by MITRE
The xz_head function in xzlib.c in libxml2 before 2.9.6 allows remote attackers to cause a denial of service (memory consumption) via a crafted LZMA file, because the decoder functionality does not restrict memory usage to what is required for a legitimate file.
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Analysis
by VulDB Data Team • 02/27/2023
The vulnerability identified as CVE-2017-18258 resides within the libxml2 library's xzlib.c component, specifically in the xz_head function that handles LZMA compressed data processing. This flaw represents a classic resource exhaustion attack vector that can be exploited by remote adversaries to consume excessive system memory. The vulnerability affects libxml2 versions prior to 2.9.6, making it a significant concern for systems that rely on XML parsing with compressed content. The issue stems from inadequate memory management within the LZMA decoder implementation, which fails to impose reasonable limits on memory allocation during decompression operations.
The technical root cause of this vulnerability aligns with CWE-770, which addresses allocation of resources without limits or with inadequate limits. When processing a crafted LZMA file, the xz_head function does not enforce memory usage constraints that would be appropriate for legitimate decompression operations. This allows an attacker to craft malicious LZMA files that, when processed by vulnerable libxml2 implementations, can trigger excessive memory consumption patterns. The decoder functionality essentially operates without bounds on memory allocation, enabling attackers to cause memory exhaustion that can lead to system instability or complete denial of service conditions.
From an operational perspective, this vulnerability poses substantial risks to systems that process XML content containing LZMA compressed data. Web applications, content management systems, and any software that utilizes libxml2 for XML parsing are potentially vulnerable. The impact extends beyond simple memory exhaustion as it can affect system availability and performance, particularly in environments where memory resources are constrained or where multiple concurrent processing threads exist. Attackers can exploit this vulnerability through various vectors including file uploads, network requests containing XML data, or any scenario where XML processing with compressed content occurs. The vulnerability is particularly concerning because it does not require authentication or special privileges to exploit, making it a straightforward denial of service attack that can be executed remotely.
The mitigation strategy for CVE-2017-18258 primarily involves upgrading to libxml2 version 2.9.6 or later, where the memory usage restrictions have been implemented. Organizations should also consider implementing additional protective measures such as input validation, file size limits, and resource monitoring to detect unusual memory consumption patterns. From an ATT&CK framework perspective, this vulnerability maps to T1499.004 - Network Denial of Service, as it enables attackers to consume system resources and cause service disruption. System administrators should also implement network segmentation and monitoring to detect potential exploitation attempts, particularly when processing XML content from untrusted sources. The vulnerability underscores the importance of proper resource management in decompression algorithms and highlights the necessity of adhering to secure coding practices that prevent unbounded resource allocation during data processing operations.