CVE-2020-25630 in Moodle
Summary
by MITRE • 12/08/2020
A vulnerability was found in Moodle where the decompressed size of zip files was not checked against available user quota before unzipping them, which could lead to a denial of service risk. This affects versions 3.9 to 3.9.1, 3.8 to 3.8.4, 3.7 to 3.7.7, 3.5 to 3.5.13 and earlier unsupported versions. Fixed in 3.9.2, 3.8.5, 3.7.8 and 3.5.14.
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Analysis
by VulDB Data Team • 12/13/2020
The vulnerability identified as CVE-2020-25630 represents a critical denial of service flaw within the Moodle learning management system that exploits improper resource management during file decompression operations. This weakness specifically targets the handling of zip file extraction processes where the system fails to validate whether the decompressed file sizes exceed the available user storage quota before proceeding with the extraction. The vulnerability exists across multiple Moodle versions including 3.9.1 and earlier, 3.8.4 and earlier, 3.7.7 and earlier, 3.5.13 and earlier, affecting organizations that rely on Moodle for educational content distribution and file management. The flaw stems from inadequate input validation and resource boundary checking mechanisms that permit malicious actors to upload specially crafted zip files designed to expand beyond normal storage limits.
The technical implementation of this vulnerability demonstrates a classic resource exhaustion attack vector where an attacker can manipulate the system's file handling process to consume excessive storage space or memory resources. When Moodle processes zip files, it should validate the total decompressed size against the user's available quota before beginning extraction, but this validation is missing or insufficient in the affected versions. This allows an attacker to upload a compressed file that appears small in size but decompresses to an enormous amount of data, effectively exhausting the user's allocated storage space or system resources. The vulnerability operates at the application layer and can be classified under CWE-400 as "Uncontrolled Resource Consumption" with potential implications for CWE-129 as "Improper Validation of Array Index" when considering the resource allocation calculations. The attack pattern aligns with ATT&CK technique T1499.001 for "Fragging" and T1566.001 for "Phishing" when considering how attackers might deliver malicious zip files through social engineering campaigns.
The operational impact of CVE-2020-25630 extends beyond simple service disruption to potentially compromise entire Moodle instances and user accounts. Organizations using affected Moodle versions face the risk of storage exhaustion attacks that can render user accounts unusable, cause system instability, and require significant administrative intervention to resolve. The vulnerability particularly affects environments where users can upload files, such as assignment submission areas, course content repositories, or general file sharing areas within Moodle. When exploited, the vulnerability can cause cascading failures including database performance degradation, application crashes, and potential denial of service for legitimate users who attempt to access their accounts or upload files. The fix implemented in versions 3.9.2, 3.8.5, 3.7.8, and 3.5.14 addresses this by introducing proper size validation checks during the decompression process, ensuring that the total decompressed size is compared against available user quota before extraction begins. System administrators should prioritize immediate patching of affected installations and consider implementing additional monitoring for unusual file upload patterns that might indicate exploitation attempts, particularly focusing on zip file uploads that exceed normal size expectations.