CVE-2020-7929 in MongoDB
Summary
by MITRE • 03/02/2021
A user authorized to perform database queries may trigger denial of service by issuing specially crafted query contain a type of regex. This issue affects: MongoDB Inc. MongoDB Server v3.6 versions prior to 3.6.21 and MongoDB Server v4.0 versions prior to 4.0.20.
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Analysis
by VulDB Data Team • 09/16/2024
This vulnerability represents a critical denial of service weakness in MongoDB database servers that allows authenticated users to disrupt system operations through carefully constructed regular expression queries. The flaw exists in the server's handling of specific regex patterns that can cause excessive resource consumption during query processing, ultimately leading to service unavailability for legitimate users. The vulnerability affects MongoDB versions 3.6.x prior to 3.6.21 and 4.0.x prior to 4.0.20, making it a widespread concern across multiple server generations. The issue stems from insufficient input validation and resource management within the database engine's regex processing subsystem, which fails to properly handle maliciously crafted patterns that can cause exponential backtracking or infinite loops during pattern matching operations.
The technical implementation of this vulnerability exploits the underlying regular expression engine's handling of certain pattern constructs that can trigger catastrophic backtracking scenarios. When a user submits a specially crafted query containing a regex pattern with nested quantifiers, alternation, or other problematic constructs, the MongoDB server's regex engine enters into computationally expensive operations that consume excessive CPU cycles and memory resources. This behavior aligns with common weaknesses documented in CWE-1321, which addresses issues related to regular expression denial of service attacks, and specifically relates to CWE-400, covering unchecked resource consumption in software systems. The vulnerability demonstrates how seemingly benign database operations can be weaponized to cause system-wide disruption when proper input sanitization and resource limits are not enforced.
From an operational perspective, this vulnerability presents significant risk to database availability and system stability, particularly in environments where database users have elevated privileges or where automated processes rely on database queries. The impact extends beyond simple service disruption to potentially affect business continuity and data access availability for legitimate users. Attackers can exploit this weakness by crafting queries that appear legitimate but contain malicious regex patterns designed to consume resources proportional to the input size, creating a denial of service condition that can persist until the system is manually restarted or the query processing is terminated. The vulnerability's exploitation requires authentication to the database system, which means that internal threats or compromised accounts can leverage this weakness to cause service disruption. This scenario aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, and demonstrates how database systems can be targeted through application-level vulnerabilities rather than network-level attacks.
Organizations should immediately apply the vendor-provided patches to MongoDB versions 3.6.21 and 4.0.20 to address this vulnerability. Additionally, implementing proper query monitoring and resource limits can help detect and prevent exploitation attempts. Database administrators should consider implementing regex validation rules and establishing query execution time limits to prevent malicious queries from consuming excessive resources. The mitigation strategy should also include network segmentation and access control measures to limit the scope of potential exploitation. Regular security assessments and penetration testing can help identify similar vulnerabilities in database configurations and applications that interface with MongoDB systems. Implementation of database activity monitoring solutions can provide early detection of suspicious query patterns that may indicate attempted exploitation of this or similar vulnerabilities.