CVE-2015-8002 in MediaWiki
Summary
by MITRE
The chunked upload API (ApiUpload) in MediaWiki before 1.23.11, 1.24.x before 1.24.4, and 1.25.x before 1.25.3 allows remote authenticated users to cause a denial of service (disk consumption) via a file upload using one byte chunks.
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Analysis
by VulDB Data Team • 04/20/2018
The vulnerability identified as CVE-2015-8002 represents a critical denial of service weakness in MediaWiki's chunked upload API implementation. This flaw affects multiple versions of the popular wiki platform, specifically targeting releases before 1.23.11, 1.24.4, and 1.25.3, creating a persistent security risk for organizations relying on MediaWiki for content management. The vulnerability stems from improper handling of file upload operations that utilize the chunked transfer encoding method, which is commonly employed for large file transfers to improve reliability and reduce memory consumption during uploads.
The technical exploitation of this vulnerability occurs through a specific attack pattern involving one-byte chunked file uploads. When authenticated users leverage the ApiUpload functionality with files broken into single-byte chunks, the MediaWiki system fails to properly validate or process these fragmented uploads. This processing error leads to excessive disk space consumption as the system creates multiple temporary file entries or maintains inefficient storage structures for each byte-sized chunk. The flaw essentially allows attackers to consume available disk resources at an accelerated rate, potentially exhausting storage capacity and rendering the affected MediaWiki instance unusable for legitimate users. This behavior aligns with CWE-400, which categorizes unchecked resource consumption as a fundamental weakness in resource management.
The operational impact of this vulnerability extends beyond simple service disruption, creating significant risks for organizations that depend on MediaWiki for collaborative content management. Attackers can systematically consume disk space by repeatedly initiating one-byte chunked uploads, effectively creating a denial of service condition that impacts not only file upload capabilities but potentially the entire system performance. The vulnerability is particularly concerning because it requires only authenticated access, meaning that users with legitimate account credentials can exploit this weakness, making it difficult to distinguish between legitimate usage and malicious activity. This characteristic places the vulnerability within the ATT&CK framework's privilege escalation and denial of service tactics, where adversaries leverage existing permissions to compromise system resources.
Organizations should prioritize immediate remediation by upgrading to patched versions of MediaWiki that address this specific chunked upload processing issue. The recommended mitigation strategy involves implementing proper input validation and resource limiting measures within the upload API to prevent excessive disk consumption from fragmented uploads. Additionally, administrators should consider implementing upload size limits and monitoring mechanisms to detect unusual upload patterns that might indicate exploitation attempts. The vulnerability highlights the importance of robust resource management in web applications and demonstrates how seemingly minor implementation flaws in API handling can create significant operational risks. Security teams should also implement network monitoring to detect abnormal upload activities and establish automated alerts when disk usage exceeds predefined thresholds, providing early warning of potential exploitation attempts.