CVE-2015-7826 in Botan
Summary
by MITRE
botan 1.11.x before 1.11.22 improperly handles wildcard matching against hostnames, which might allow remote attackers to have unspecified impact via a valid X.509 certificate, as demonstrated by accepting *.example.com as a match for bar.foo.example.com.
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Analysis
by VulDB Data Team • 08/28/2020
The vulnerability identified as CVE-2015-7826 affects the Botan cryptographic library version 1.11.x prior to 1.11.22, specifically addressing a critical flaw in the X.509 certificate validation process. This issue stems from improper handling of wildcard certificate matching against hostnames, creating a significant security weakness that could be exploited by remote attackers to bypass certificate validation mechanisms. The flaw manifests when the library processes wildcard certificates, particularly those with patterns like *.example.com, which should only be valid for subdomains of example.com but are incorrectly accepted for arbitrary hostnames within the domain hierarchy.
The technical implementation of this vulnerability resides in the certificate validation algorithm where the wildcard matching logic fails to properly enforce the constraints defined in RFC 6125 for X.509 certificate subject alternative name validation. When a certificate contains a wildcard pattern such as .example.com, the system should only validate that the hostname being connected to is a direct subdomain of example.com, not that it matches any arbitrary hostname structure. The flaw allows the system to accept a certificate with the pattern .example.com as valid for a hostname like bar.foo.example.com, which violates the fundamental security principle that wildcard certificates should only match a single level of subdomain depth.
This vulnerability creates unspecified but potentially severe operational impacts across systems utilizing the affected Botan library, particularly in environments where SSL/TLS connections rely on proper certificate validation. Attackers could exploit this weakness to perform man-in-the-middle attacks by presenting valid certificates that should not be accepted for certain hostnames, potentially compromising the integrity of secure communications. The impact extends beyond simple certificate validation failures, as it undermines the trust model that secure network communications depend upon, potentially allowing unauthorized parties to establish seemingly legitimate secure connections to services they should not be able to access.
The vulnerability aligns with CWE-295, which addresses "Improper Certificate Validation," and demonstrates characteristics consistent with ATT&CK technique T1552.001 for "Credentials in Files," as it affects the fundamental certificate validation process that protects sensitive communications. Organizations using Botan versions prior to 1.11.22 should immediately implement the available patch to address this issue, as the vulnerability affects the core security functionality of the library. Additionally, system administrators should conduct thorough audits of all systems utilizing the Botan library to ensure that certificate validation is functioning correctly and that no services are vulnerable to this type of certificate forgery attack.
The fix for CVE-2015-7826 involves updating to Botan version 1.11.22 or later, which includes corrected wildcard matching algorithms that properly enforce the constraints of RFC 6125. This update ensures that wildcard certificates are only accepted for hostnames that conform to the expected subdomain matching patterns, preventing the acceptance of certificates for arbitrary hostname structures that could be exploited by malicious actors. The patch addresses the root cause by implementing stricter validation rules for wildcard certificate matching, thereby restoring the intended security properties of X.509 certificate validation within the Botan cryptographic library.