CVE-2026-66749 in Lets Chat
Summary
by MITRE • 07/28/2026
Let's Chat 0.4.0 through 0.4.8 contains a null dereference vulnerability that allows authenticated attackers to crash the server by supplying a valid 24-character hex string room parameter that matches no document in the database. Attackers can send a crafted GET /messages request causing an uncaught TypeError in an asynchronous Mongoose callback that terminates the Node.js server process, with the same defect reachable through multiple code paths including the socket.io interface.
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Analysis
by VulDB Data Team • 07/28/2026
This vulnerability exists within Let's Chat versions 0.4.0 through 0.4.8 and represents a critical null dereference flaw that can be exploited by authenticated attackers to cause remote server crashes. The vulnerability manifests when an attacker supplies a valid 24-character hexadecimal string as a room parameter that does not correspond to any existing document in the database. This specific input triggers an unhandled TypeError within the asynchronous Mongoose callback mechanism, leading to abrupt termination of the Node.js server process and complete service disruption. The flaw demonstrates poor error handling practices where the application fails to properly validate or handle cases where database queries return null or undefined results.
The technical execution path involves sending a crafted GET /messages request that bypasses normal input validation procedures. When Mongoose processes the query with the non-existent room parameter, the asynchronous callback fails to account for scenarios where document lookup returns no results, resulting in an uncaught TypeError exception that crashes the entire server process. This vulnerability is particularly dangerous because it can be triggered through multiple code paths including both RESTful API endpoints and the socket.io interface, providing attackers with several potential attack vectors. The asynchronous nature of the callback execution means that the error occurs outside the normal request handling flow, making it difficult to detect and prevent through standard input validation measures.
The operational impact of this vulnerability extends beyond simple service disruption as it represents a denial-of-service condition that can be exploited by authenticated users with minimal privileges. Attackers need only valid authentication credentials to exploit this flaw, eliminating the requirement for privilege escalation or complex attack chains. The crash occurs at the Node.js process level, requiring manual restart of the application and potentially resulting in data loss or session disruption for legitimate users. This vulnerability directly maps to CWE-476 which describes null pointer dereference conditions, and aligns with ATT&CK technique T1499.004 which covers network disruption through service exhaustion or termination.
Mitigation strategies should focus on implementing comprehensive error handling within all database query operations, particularly around asynchronous Mongoose callbacks where null results are possible. The application code must validate all database query outcomes and explicitly handle cases where documents do not exist rather than allowing unhandled exceptions to propagate. Input sanitization should include validation of room parameter existence before processing, and defensive programming practices should be implemented to ensure that all potential execution paths properly account for edge cases including empty or null results from database operations. Additionally, implementing proper exception handling middleware at the Node.js application level can help catch these unhandled errors before they terminate the process, while also logging the incidents for security monitoring purposes.