CVE-2017-11770 in .NET Framework
Summary
by MITRE
.NET Core 1.0, 1.1, and 2.0 allow an unauthenticated attacker to remotely cause a denial of service attack against a .NET Core web application by improperly parsing certificate data. A denial of service vulnerability exists when .NET Core improperly handles parsing certificate data, aka ".NET CORE Denial Of Service Vulnerability".
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Analysis
by VulDB Data Team • 01/10/2023
The vulnerability identified as CVE-2017-11770 represents a critical denial of service weakness affecting Microsoft .NET Core versions 1.0, 1.1, and 2.0. This flaw resides in the certificate parsing mechanism within the .NET Core runtime environment, specifically when handling X.509 certificate data during web application operations. The vulnerability stems from inadequate input validation and error handling within the certificate processing pipeline, creating a condition where malformed or specially crafted certificate data can trigger unexpected behavior in the application runtime.
The technical exploitation of this vulnerability occurs when a remote attacker sends malformed certificate data to a .NET Core web application that is configured to accept client certificates or perform certificate validation operations. The flaw manifests as improper parsing of certificate structures, particularly when the application attempts to process certificate chains or individual certificate objects. When the .NET Core runtime encounters malformed certificate data, it fails to properly validate the input and instead enters an infinite loop or consumes excessive system resources during the parsing process. This behavior results in the application becoming unresponsive and unable to process legitimate requests, effectively creating a denial of service condition that can be triggered without any authentication requirements.
From an operational perspective, this vulnerability poses significant risks to web applications deployed on .NET Core platforms, particularly those that handle client certificate authentication or perform certificate validation as part of their security protocols. The impact extends beyond simple service disruption as the vulnerability can be exploited at scale, potentially affecting multiple applications simultaneously if they share the same vulnerable runtime environment. The lack of authentication requirements makes this attack vector particularly dangerous as it can be executed by any remote attacker without prior access credentials, making it an attractive target for malicious actors seeking to disrupt services. Organizations running .NET Core applications in production environments face potential business disruption, increased operational overhead for incident response, and possible reputational damage from service unavailability.
The vulnerability aligns with CWE-129, which addresses improper validation of certificate data, and can be mapped to ATT&CK technique T1499.004 for network denial of service attacks. Microsoft addressed this vulnerability through security updates that improved input validation and error handling within the certificate parsing components of .NET Core. Organizations should implement immediate mitigation strategies including applying the relevant security patches, configuring application firewalls to restrict certificate-related traffic, and monitoring for unusual certificate processing patterns. Additionally, implementing proper certificate validation controls and reducing the attack surface by limiting client certificate requirements can help minimize exposure to this vulnerability. The remediation process requires careful testing of updated runtime environments to ensure compatibility while addressing the underlying certificate parsing flaws that enabled the denial of service condition.