CVE-2011-4577 in OpenSSL
Summary
by MITRE
OpenSSL before 0.9.8s and 1.x before 1.0.0f, when RFC 3779 support is enabled, allows remote attackers to cause a denial of service (assertion failure) via an X.509 certificate containing certificate-extension data associated with (1) IP address blocks or (2) Autonomous System (AS) identifiers.
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Analysis
by VulDB Data Team • 08/08/2024
The vulnerability described in CVE-2011-4577 represents a critical denial of service flaw within OpenSSL implementations that affects versions prior to 0.9.8s and 1.0.0f. This issue specifically manifests when the OpenSSL library processes X.509 certificates that contain RFC 3779 extension data, which is designed to support IP address blocks and Autonomous System identifiers. The flaw stems from inadequate validation of certificate extension data, leading to assertion failures that crash the application. This vulnerability operates at the cryptographic library level, making it particularly dangerous as it can affect any application that relies on OpenSSL for secure communications including web servers, email servers, and other network services that handle X.509 certificates.
The technical implementation of this vulnerability involves the processing of RFC 3779 certificate extensions that are used to specify IP address ranges and AS identifiers in certificates. When OpenSSL encounters malformed or improperly structured certificate extension data within these specific extensions, the library's internal assertion checks fail, causing an abrupt termination of the application process. This behavior occurs because the validation logic does not properly handle edge cases or malformed data within the certificate extension fields, particularly when dealing with IP address block or AS identifier data. The assertion failure represents a fundamental flaw in the library's error handling mechanism, where the software assumes certain data structures will always conform to expected formats without proper bounds checking or validation.
From an operational standpoint, this vulnerability presents a significant risk to systems that process X.509 certificates from untrusted sources, particularly in environments where certificate validation is performed automatically without manual intervention. Attackers can exploit this weakness by constructing malicious X.509 certificates with specifically crafted RFC 3779 extensions that trigger the assertion failure when processed by vulnerable OpenSSL implementations. The impact extends beyond simple service disruption as this vulnerability can be leveraged to create widespread denial of service conditions across multiple applications and services that depend on OpenSSL. The vulnerability aligns with CWE-611, which addresses improper restriction of XML external entity reference, and demonstrates how certificate validation flaws can lead to system instability. The attack surface includes any system that validates certificates, including web servers, email servers, SSL/TLS clients, and certificate authorities that process certificate requests.
The recommended mitigations for CVE-2011-4577 involve immediate upgrading of OpenSSL implementations to versions 0.9.8s or 1.0.0f and later, which contain the necessary patches to properly handle RFC 3779 certificate extensions. Organizations should also consider disabling RFC 3779 support in OpenSSL configurations when this functionality is not required, as a temporary workaround. Additionally, implementing proper certificate validation procedures that include checking for malformed extensions and monitoring for unusual certificate processing patterns can help detect potential exploitation attempts. The vulnerability demonstrates the importance of robust input validation in cryptographic libraries and aligns with ATT&CK technique T1499.004, which covers network denial of service attacks through protocol manipulation. System administrators should also consider implementing certificate pinning mechanisms and regular security assessments to prevent exploitation of similar vulnerabilities in the cryptographic infrastructure.