CVE-2016-2850 in Botan
Summary
by MITRE
Botan 1.11.x before 1.11.29 does not enforce TLS policy for (1) signature algorithms and (2) ECC curves, which allows remote attackers to conduct downgrade attacks via unspecified vectors.
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Analysis
by VulDB Data Team • 08/19/2022
The vulnerability identified as CVE-2016-2850 affects the Botan cryptographic library version 1.11.x prior to 1.11.29, representing a significant weakness in TLS protocol enforcement that exposes systems to sophisticated downgrade attacks. This flaw specifically targets two critical aspects of TLS security implementation where the library fails to properly validate signature algorithms and elliptic curve cryptography parameters during the handshake process. The vulnerability stems from insufficient policy enforcement mechanisms within the cryptographic library, allowing malicious actors to manipulate TLS negotiations and force connections to use weaker cryptographic primitives than initially negotiated. The impact extends beyond simple security degradation as it creates opportunities for active attack vectors that can compromise the integrity and confidentiality of encrypted communications.
The technical nature of this vulnerability lies in the library's failure to validate cryptographic parameters against established security policies during TLS handshake operations. When the Botan library processes TLS connections, it should enforce strict adherence to security policies governing acceptable signature algorithms and elliptic curve choices, but this enforcement mechanism was absent or incomplete in affected versions. This allows attackers to exploit the lack of validation by presenting forged certificate chains or manipulating the cryptographic negotiation process to downgrade connections to less secure configurations. The unspecified vectors mentioned in the description suggest that the attack could be executed through various means including man-in-the-middle scenarios, proxy manipulation, or direct protocol interference. The vulnerability operates at the protocol level where cryptographic strength decisions are made, making it particularly dangerous as it undermines the fundamental security assumptions of TLS implementations.
From an operational standpoint, this vulnerability creates substantial risk for systems relying on Botan for TLS functionality, potentially enabling attackers to bypass security measures designed to prevent the use of weak cryptographic algorithms. The downgrade attack capability means that even if a client and server negotiate strong cryptographic parameters initially, an attacker can force the connection to use weaker alternatives, effectively nullifying security improvements. This vulnerability affects the core security posture of applications using Botan, particularly those in environments where TLS security is paramount such as financial services, healthcare systems, and government communications. The impact is amplified because the flaw exists in a widely used cryptographic library, meaning that numerous applications and systems could be simultaneously vulnerable. Organizations may experience data breaches, unauthorized access, or compromised communications if they are running affected versions of the library.
The mitigation strategy for CVE-2016-2850 requires immediate upgrade to Botan version 1.11.29 or later, which includes the necessary policy enforcement mechanisms for signature algorithms and ECC curves. System administrators should conduct comprehensive inventory checks to identify all systems using affected Botan versions and prioritize patching efforts accordingly. Additional defensive measures include implementing strict TLS policy enforcement at network boundaries, monitoring for unusual cryptographic negotiation patterns, and conducting regular security audits of cryptographic implementations. Organizations should also consider implementing certificate pinning mechanisms and enhanced logging to detect potential downgrade attempts. From a compliance perspective, this vulnerability aligns with CWE-327 (Use of a Broken or Risky Cryptographic Algorithm) and represents a weakness in the TLS implementation that could be categorized under ATT&CK technique T1071.004 (Application Layer Protocol: DNS) when used in conjunction with DNS-based attack vectors. The vulnerability demonstrates the critical importance of proper cryptographic policy enforcement and serves as a reminder that even well-established libraries can contain security gaps that require vigilant monitoring and timely remediation.