CVE-2016-10536 in engine.io-client
Summary
by MITRE
engine.io-client is the client for engine.io, the implementation of a transport-based cross-browser/cross-device bi-directional communication layer for Socket.IO. The vulnerability is related to the way that node.js handles the `rejectUnauthorized` setting. If the value is something that evaluates to false, certificate verification will be disabled. This is problematic as engine.io-client 1.6.8 and earlier passes in an object for settings that includes the rejectUnauthorized property, whether it has been set or not. If the value has not been explicitly changed, it will be passed in as `null`, resulting in certificate verification being turned off.
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Analysis
by VulDB Data Team • 03/17/2023
The vulnerability identified as CVE-2016-10536 affects the engine.io-client library version 1.6.8 and earlier, which serves as the client component for engine.io, a critical transport layer for Socket.IO applications. This flaw represents a significant security weakness in how the library handles SSL/TLS certificate verification within node.js environments. The vulnerability stems from improper handling of the rejectUnauthorized configuration parameter, which controls whether SSL certificates should be validated during secure connections. When this parameter evaluates to a falsy value, certificate verification is disabled, leaving applications susceptible to man-in-the-middle attacks and other cryptographic threats.
The technical implementation flaw occurs within the engine.io-client library's parameter handling mechanism where it passes configuration objects containing the rejectUnauthorized property to the underlying node.js SSL implementation. Specifically, when users do not explicitly set this property, the library defaults to passing null as the value, which in node.js context evaluates to false and consequently disables certificate validation. This behavior violates fundamental security principles and creates an implicit trust model that undermines the security assurances provided by SSL/TLS protocols. The vulnerability is classified under CWE-295 which specifically addresses improper certificate validation, and aligns with ATT&CK technique T1566 related to credential access through network sniffing and man-in-the-middle attacks.
The operational impact of this vulnerability is substantial as it affects any application using engine.io-client version 1.6.8 or earlier that establishes secure WebSocket connections through the engine.io transport layer. Applications become vulnerable to attacks where malicious actors can intercept and manipulate communications between clients and servers, potentially gaining access to sensitive data, session tokens, or other confidential information. The flaw is particularly dangerous in production environments where secure communication is paramount, as the vulnerability can remain undetected while silently disabling critical security controls. Network monitoring tools may not immediately flag this as an issue since the connection appears to establish successfully, but the cryptographic security is fundamentally compromised.
Mitigation strategies for CVE-2016-10536 primarily involve upgrading to engine.io-client version 1.6.9 or later, where the library properly handles the rejectUnauthorized parameter by either explicitly setting it to true or ensuring that null values are properly converted to boolean true. Administrators should also implement explicit configuration management practices that require developers to explicitly set security parameters rather than relying on default behaviors. Additional protective measures include implementing network-level monitoring to detect anomalous SSL/TLS behavior, conducting regular security audits of client-side libraries, and establishing secure coding practices that prevent implicit security parameter handling. Organizations should also consider implementing certificate pinning mechanisms as an additional defense in depth strategy, though the primary fix remains the library upgrade to address the root cause of the improper null value handling that disables certificate verification.