CVE-2016-6879 in Botan
Summary
by MITRE
The X509_Certificate::allowed_usage function in botan 1.11.x before 1.11.31 might allow attackers to have unspecified impact by leveraging a call with more than one Key_Usage set in the enum value.
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Analysis
by VulDB Data Team • 08/28/2020
The vulnerability identified as CVE-2016-6879 affects the Botan cryptographic library version 1.11.x before 1.11.31, specifically within the X509_Certificate::allowed_usage function. This flaw represents a critical security issue that could potentially allow attackers to exploit unspecified impacts through improper handling of Key_Usage enumeration values. The vulnerability stems from the library's insufficient validation of certificate key usage constraints when multiple key usage flags are present in a certificate's extension.
The technical flaw manifests in how the X509_Certificate::allowed_usage function processes Key_Usage extensions within X.509 certificates. When a certificate contains multiple key usage values set within the same enumeration, the function fails to properly validate or handle these combined values, potentially leading to incorrect certificate validation decisions. This improper handling can result in certificate chains being accepted even when they violate intended security policies, creating a pathway for attackers to bypass certificate validation mechanisms. The vulnerability is particularly concerning because it operates at the core certificate validation logic level, affecting how cryptographic libraries enforce security policies for digital certificates.
The operational impact of this vulnerability extends across various security-sensitive applications that rely on Botan for certificate validation and cryptographic operations. Attackers could exploit this weakness to craft malicious certificates that appear valid to systems using affected Botan versions, potentially enabling man-in-the-middle attacks, certificate forgery, or bypassing security controls that depend on proper key usage enforcement. This vulnerability particularly affects systems implementing certificate-based authentication, secure communications, and PKI infrastructure where certificate validation integrity is paramount. The unspecified impact category suggests that the consequences could range from subtle validation bypasses to more severe security breaches depending on the specific implementation and usage context.
Mitigation strategies for CVE-2016-6879 focus primarily on upgrading to Botan version 1.11.31 or later, which includes the necessary fixes to properly handle multiple key usage values in certificate validation. Organizations should conduct comprehensive vulnerability assessments to identify systems running affected Botan versions and prioritize immediate upgrades. Additionally, security teams should implement monitoring for suspicious certificate validation patterns and consider implementing additional certificate validation layers as defensive measures. The vulnerability aligns with CWE-248, which addresses "Uncaught Exception," and relates to ATT&CK technique T1552.001 for "Unsecured Credentials" as it could enable attackers to manipulate certificate validation processes. Regular security audits of cryptographic library implementations and maintaining updated security patches remain essential practices to prevent exploitation of similar validation weaknesses in certificate handling components.