CVE-2021-29469 in Node-redis
Summary
by MITRE • 04/24/2021
Node-redis is a Node.js Redis client. Before version 3.1.1, when a client is in monitoring mode, the regex begin used to detected monitor messages could cause exponential backtracking on some strings. This issue could lead to a denial of service. The issue is patched in version 3.1.1.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 04/29/2021
The vulnerability identified as CVE-2021-29469 affects the Node-redis library, a widely-used Node.js client for Redis database operations. This issue specifically targets the monitoring mode functionality within the client library, where the implementation contains a flawed regular expression pattern that creates opportunities for malicious input to trigger performance degradation. The affected version range includes all releases prior to 3.1.1, making it a significant concern for applications that utilize monitoring capabilities in their Redis client implementations. The vulnerability represents a classic example of a regular expression denial of service (ReDoS) attack vector that can severely impact system availability and performance.
The technical flaw manifests in the monitoring mode where the Node-redis client attempts to parse and process monitor messages from the Redis server. The vulnerable regex pattern exhibits exponential backtracking behavior when processing specially crafted input strings that match the pattern structure. This occurs when the regular expression engine attempts to match input strings that cause it to explore multiple potential matches through backtracking, leading to computational complexity that grows exponentially with input length. The regex pattern fails to properly handle certain string combinations that create nested backtracking scenarios, allowing an attacker to craft inputs that cause the regular expression engine to consume excessive CPU cycles and memory resources.
The operational impact of this vulnerability extends beyond simple performance degradation to potentially causing complete system unresponsiveness or application crashes. When an attacker exploits this vulnerability, they can send malicious monitor messages that trigger the exponential backtracking behavior, effectively consuming all available CPU resources on the system running the Node-redis client. This denial of service condition affects not just individual application instances but can potentially impact entire infrastructure components that rely on Redis monitoring for operational insights. The vulnerability is particularly concerning in production environments where monitoring mode is actively used, as it can be exploited without requiring authentication or special privileges, making it an attractive target for attackers seeking to disrupt services.
The fix implemented in version 3.1.1 addresses the root cause by modifying the regular expression pattern to eliminate the backtracking vulnerability while maintaining the intended functionality of monitor message parsing. This patch demonstrates the importance of proper input validation and regex design in security-critical components. The vulnerability aligns with CWE-400, which catalogs weaknesses related to resource exhaustion, and specifically relates to the ReDoS category. From an ATT&CK framework perspective, this vulnerability could be leveraged as part of a broader attack chain under the T1499.004 technique for network denial of service, potentially leading to system availability compromise and service disruption. Organizations should prioritize updating to version 3.1.1 or later to mitigate this vulnerability, while also implementing monitoring for unusual CPU usage patterns that might indicate exploitation attempts. The incident underscores the critical importance of regex security testing and the potential for seemingly benign functionality to become attack vectors when not properly validated against malicious inputs.