CVE-2017-13099 in wolfSSL
Summary
by MITRE
wolfSSL prior to version 3.12.2 provides a weak Bleichenbacher oracle when any TLS cipher suite using RSA key exchange is negotiated. An attacker can recover the private key from a vulnerable wolfSSL application. This vulnerability is referred to as "ROBOT."
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Analysis
by VulDB Data Team • 12/30/2024
The vulnerability identified as CVE-2017-13099 represents a critical cryptographic flaw in wolfSSL versions prior to 3.12.2 that fundamentally compromises the security of RSA key exchange implementations. This weakness manifests as a weak Bleichenbacher oracle, a specific type of cryptographic vulnerability that arises from improper error handling during RSA decryption operations. The flaw specifically affects TLS cipher suites that utilize RSA key exchange, creating a pathway for attackers to systematically recover the private key of vulnerable applications through a series of carefully crafted cryptographic operations. The vulnerability has been classified under CWE-310 as "Cryptographic Algorithm Weakness" and is particularly significant because it enables attackers to perform sophisticated key recovery attacks that were previously thought to be computationally infeasible.
The operational impact of this vulnerability extends far beyond simple cryptographic weakness, as it fundamentally undermines the confidentiality and integrity guarantees that RSA key exchange is designed to provide. When an attacker successfully exploits this vulnerability through the ROBOT attack vector, they can reconstruct the private key of the TLS server, which allows them to impersonate the server, decrypt previously captured communications, and potentially compromise the entire TLS infrastructure. This attack is particularly dangerous because it operates at the protocol level, affecting the core cryptographic foundations that secure web communications. The vulnerability affects all TLS cipher suites that rely on RSA key exchange, making it particularly widespread across applications that have not updated to patched versions of wolfSSL.
The technical exploitation of this vulnerability follows the established patterns of Bleichenbacher's attack on RSA PKCS#1 v1.5 padding, where the attacker can determine valid padding through timing or error responses from the server. In the context of wolfSSL, the weak oracle occurs during the RSA decryption process when the application fails to properly handle error conditions that reveal information about the validity of padding. This information leakage, even when minimal, accumulates over multiple requests to enable the attacker to reconstruct the private key through mathematical techniques that exploit the statistical properties of the padding oracle. The attack can be executed remotely without requiring privileged access, making it particularly dangerous for web servers and applications that handle sensitive communications. Organizations implementing security controls should reference ATT&CK technique T1593 for reconnaissance activities related to cryptographic key recovery and T1583 for infrastructure attacks targeting cryptographic implementations.
Mitigation strategies for CVE-2017-13099 require immediate action to update wolfSSL implementations to version 3.12.2 or later, which includes proper error handling that prevents the information leakage that enables the attack. Organizations should also consider transitioning away from RSA key exchange cipher suites toward more secure alternatives such as ECDHE-based cipher suites that do not suffer from this vulnerability. Additionally, network administrators should implement monitoring for unusual cryptographic operations and consider deploying cryptographic libraries that have undergone thorough security auditing for similar vulnerabilities. The fix implemented in wolfSSL 3.12.2 addresses the root cause by ensuring that error responses during RSA operations are uniform and do not reveal information about padding validity, thereby eliminating the oracle that enabled the attack. Security teams should also conduct comprehensive vulnerability assessments to identify other potential instances of similar weaknesses in cryptographic implementations across their infrastructure.