CVE-2017-16136 in method-override
Summary
by MITRE
method-override is a module used by the Express.js framework to let you use HTTP verbs such as PUT or DELETE in places where the client doesn't support it. method-override is vulnerable to a regular expression denial of service vulnerability when specially crafted input is passed in to be parsed via the X-HTTP-Method-Override header.
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Analysis
by VulDB Data Team • 02/16/2020
The CVE-2017-16136 vulnerability resides within the method-override middleware component of the Express.js web application framework, which serves as a critical middleware layer for handling HTTP verb overrides. This module enables web applications to accept PUT and DELETE HTTP methods even when clients cannot natively support them, typically through the X-HTTP-Method-Override header. The vulnerability manifests as a regular expression denial of service flaw that occurs when maliciously crafted input is processed through the header parsing mechanism, creating a potential avenue for service disruption.
The technical flaw exploits the regular expression patterns used by method-override to parse the X-HTTP-Method-Override header values. When an attacker submits specially crafted input that triggers catastrophic backtracking in the regular expression engine, the parsing process becomes computationally expensive and can consume excessive CPU resources. This vulnerability falls under the CWE-400 category of Uncontrolled Resource Consumption, specifically addressing Regular Expression Denial of Service attacks. The attack vector leverages the middleware's failure to properly validate or sanitize input before processing it through regex patterns, allowing an attacker to craft input that causes the regular expression engine to perform exponential time complexity operations.
The operational impact of this vulnerability extends beyond simple denial of service, as it can potentially disrupt the entire web application's ability to process legitimate requests. Attackers can exploit this weakness by sending malicious payloads that cause the application server to become unresponsive or consume excessive computational resources, effectively creating a denial of service condition. The vulnerability affects applications using Express.js versions prior to 4.15.5, making it particularly concerning for organizations with legacy systems or applications that have not been properly updated. This type of attack aligns with ATT&CK technique T1499.004 for Network Denial of Service, where adversaries leverage application-level vulnerabilities to exhaust system resources.
Mitigation strategies for CVE-2017-16136 primarily involve updating the method-override middleware to version 1.3.4 or higher, which includes fixed regular expression patterns that prevent catastrophic backtracking scenarios. Organizations should also implement input validation and sanitization measures at the application level to filter out potentially malicious headers before they reach the middleware components. Additionally, network-level protections such as rate limiting and header validation can provide defense-in-depth measures against exploitation attempts. The vulnerability highlights the importance of regularly updating third-party dependencies and conducting thorough security assessments of middleware components within web application frameworks, as these components often serve as attack surfaces that can be leveraged for broader system compromise.