CVE-2018-16870 in wolfSSL
Summary
by MITRE
It was found that wolfssl before 3.15.7 is vulnerable to a new variant of the Bleichenbacher attack to perform downgrade attacks against TLS. This may lead to leakage of sensible data.
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Analysis
by VulDB Data Team • 08/31/2025
The vulnerability identified as CVE-2018-16870 represents a critical security flaw in wolfSSL versions prior to 3.15.7, specifically targeting the TLS protocol's cryptographic handshake mechanism. This vulnerability enables attackers to perform sophisticated downgrade attacks by exploiting weaknesses in the RSA decryption process during TLS negotiation, creating a significant risk for sensitive data exposure. The issue stems from the implementation's susceptibility to a novel variant of the Bleichenbacher attack, which has historically been used to compromise RSA-based cryptographic systems by manipulating padding schemes during decryption operations.
The technical flaw manifests in wolfSSL's handling of RSA decryption operations within the TLS protocol, where the implementation fails to properly validate padding schemes during the decryption process. This weakness allows malicious actors to send specially crafted padding values that, when processed by the vulnerable SSL library, reveal information about the plaintext being decrypted. The vulnerability specifically affects the TLS protocol's RSA key exchange mechanism, where the server's private key decryption operations are subjected to timing and padding oracle attacks. The attack vector operates by exploiting the difference in error handling between valid and invalid padding schemes, enabling an attacker to gradually reconstruct the plaintext through multiple decryption attempts.
The operational impact of this vulnerability extends beyond simple data leakage, as it fundamentally compromises the confidentiality guarantees provided by TLS encryption. Attackers can exploit this weakness to perform man-in-the-middle attacks, intercept and modify sensitive communications, and potentially gain access to authentication credentials, personal information, and proprietary data transmitted over affected systems. The vulnerability affects any application or service using wolfSSL versions before 3.15.7 in TLS configurations that rely on RSA key exchange, making it particularly dangerous for web servers, email systems, and any network infrastructure handling confidential data. The attack's effectiveness increases with network proximity and the ability to perform multiple attack iterations, making it a significant concern for organizations with exposed TLS endpoints.
Mitigation strategies for CVE-2018-16870 require immediate patching of affected wolfSSL implementations to version 3.15.7 or later, which includes enhanced padding validation and improved resistance to Bleichenbacher-style attacks. Organizations should also implement additional security controls such as disabling RSA key exchange in TLS configurations where possible, implementing proper certificate validation procedures, and monitoring network traffic for signs of attempted exploitation. The fix addresses the underlying cryptographic implementation by strengthening padding verification mechanisms and introducing proper error handling that prevents information leakage through timing variations. This vulnerability aligns with CWE-327, which focuses on weak cryptographic algorithms and improper implementation of cryptographic protocols, and maps to ATT&CK technique T1041 for data manipulation and T1566 for credential access through network attacks. System administrators must also consider implementing network segmentation and intrusion detection systems to monitor for potential exploitation attempts, as the vulnerability's impact can be amplified in environments with multiple exposed services using the affected cryptographic library.