CVE-2021-45945 in uWebSockets
Summary
by MITRE • 01/01/2022
uWebSockets 19.0.0 through 20.8.0 has an out-of-bounds write in std::__1::pair uWS::HttpParser::fenceAndConsumePostPadded
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Analysis
by VulDB Data Team • 01/05/2022
The vulnerability CVE-2021-45945 affects uWebSockets versions 19.0.0 through 20.8.0 and represents a critical out-of-bounds write condition within the HttpParser component. This flaw occurs during the processing of HTTP requests where the application fails to properly validate input data before performing memory operations. The specific function implicated is uWS::HttpParser::fenceAndConsumePostPadded which handles post-padded data during HTTP parsing operations. The vulnerability stems from inadequate bounds checking when processing HTTP request data that may contain maliciously crafted padding or malformed content. This type of vulnerability falls under CWE-787 Out-of-bounds Write, which is classified as a memory safety issue that can lead to arbitrary code execution or system compromise. The issue is particularly concerning because uWebSockets is a high-performance HTTP server library commonly used in web applications and microservices architectures.
The technical exploitation of this vulnerability requires an attacker to craft specific HTTP requests that trigger the vulnerable code path within the parser. When the HttpParser processes malformed or specially crafted HTTP data, the fenceAndConsumePostPadded function attempts to write data beyond the allocated memory boundaries of an internal std::__1::pair structure. This occurs because the function does not properly validate the length of incoming data against the bounds of its internal buffers before performing write operations. The flaw is particularly dangerous in server environments where uWebSockets is used as a backend component, as it could allow remote attackers to execute arbitrary code on the affected system. The vulnerability demonstrates a classic buffer overflow pattern where insufficient input validation leads to memory corruption, potentially enabling privilege escalation or denial of service conditions.
From an operational impact perspective, this vulnerability poses significant risks to organizations utilizing uWebSockets in production environments. The out-of-bounds write can result in application crashes, data corruption, or more severely, remote code execution depending on the system configuration and memory layout. Attackers could exploit this vulnerability to gain unauthorized access to systems running affected versions of uWebSockets, potentially leading to complete system compromise. The vulnerability affects both web servers and microservices that rely on uWebSockets for HTTP handling, making it a widespread concern across various deployment scenarios. Organizations using this library in critical infrastructure, financial services, or healthcare applications face heightened risk due to potential data breaches and service disruptions. The vulnerability also aligns with ATT&CK technique T1203 Exploitation for Client Execution, as it enables remote code execution through HTTP request manipulation.
Mitigation strategies for CVE-2021-45945 involve immediate patching of affected uWebSockets versions to the latest stable releases where the vulnerability has been addressed. Organizations should implement network segmentation and monitoring to detect suspicious HTTP traffic patterns that might indicate exploitation attempts. Input validation should be strengthened at all levels of the application stack, including implementing proper bounds checking and sanitization of HTTP request data. Security teams should consider implementing intrusion detection systems that can identify anomalous HTTP request patterns associated with this vulnerability. Additionally, regular security assessments and vulnerability scanning should be conducted to identify other potential issues in the application stack. The fix typically involves updating to uWebSockets version 20.9.0 or later, which includes proper bounds checking and memory validation in the HttpParser component. Organizations should also implement proper access controls and least privilege principles to limit the potential impact if exploitation occurs, as well as maintain comprehensive backup and recovery procedures to ensure business continuity in case of successful attacks.