CVE-2021-3446 in libtpms
Summary
by MITRE • 03/25/2021
A flaw was found in libtpms in versions before 0.8.2. The commonly used integration of libtpms with OpenSSL contained a vulnerability related to the returned IV (initialization vector) when certain symmetric ciphers were used. Instead of returning the last IV it returned the initial IV to the caller, thus weakening the subsequent encryption and decryption steps. The highest threat from this vulnerability is to data confidentiality.
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Analysis
by VulDB Data Team • 04/05/2021
The vulnerability identified as CVE-2021-3446 resides within the libtpms library, a critical component for TPM (Trusted Platform Module) functionality in security-critical systems. This flaw specifically affects versions prior to 0.8.2 and represents a serious cryptographic weakness that undermines the integrity of encrypted communications. The issue manifests in the integration between libtpms and OpenSSL, where the library fails to properly handle initialization vectors during symmetric cipher operations, creating a fundamental flaw in the encryption process that directly impacts data confidentiality.
The technical root cause of this vulnerability stems from improper handling of initialization vectors within the cryptographic implementation. When symmetric ciphers are employed, the library incorrectly returns the initial IV value instead of the expected final IV value to the calling application. This seemingly minor deviation has profound implications for cryptographic security as it fundamentally weakens the encryption and decryption processes. The IV is a critical component in symmetric encryption algorithms, particularly in modes like CBC (Cipher Block Chaining) where the IV ensures that identical plaintext blocks encrypt to different ciphertext blocks. By returning the wrong IV, the system effectively reduces the entropy and security of the encryption process, making it more susceptible to pattern analysis and cryptographic attacks.
The operational impact of this vulnerability extends beyond simple data confidentiality concerns, affecting the entire security posture of systems relying on libtpms for secure cryptographic operations. Systems utilizing this library for TPM functionality, including those implementing secure boot processes, key management, and hardware security modules, face significant risks. The weakness creates opportunities for attackers to potentially reconstruct plaintext data from encrypted communications, especially when the same IV is used multiple times or when pattern recognition techniques can be applied to the flawed encryption process. This vulnerability aligns with CWE-329, which specifically addresses the improper generation or use of initialization vectors, and represents a clear violation of cryptographic best practices.
From an attack perspective, this vulnerability enables potential adversaries to exploit the flawed encryption implementation through various means including ciphertext-only attacks and pattern analysis techniques. The ATT&CK framework categorizes this as a cryptographic weakness that could be leveraged in the credential access and defense evasion phases of an attack lifecycle. The impact is particularly severe for systems where TPM functionality is critical, such as in enterprise security infrastructure, cloud computing environments, and embedded systems requiring hardware-based security. Organizations implementing solutions that depend on libtpms for secure cryptographic operations must consider this vulnerability as a critical threat to their data protection mechanisms, potentially requiring immediate remediation and system re-evaluation.
The mitigation strategy for CVE-2021-3446 involves immediate upgrading of libtpms to version 0.8.2 or later, which contains the necessary fixes to properly handle initialization vectors during symmetric cipher operations. System administrators should also conduct comprehensive vulnerability assessments to identify all systems utilizing affected versions of libtpms, particularly those in security-critical environments. Additional measures include monitoring for any signs of cryptographic attacks or data breaches that may have occurred during the period when vulnerable systems were operational, and implementing proper key rotation procedures to ensure that any compromised data remains protected. The fix addresses the core cryptographic implementation issue by ensuring that the correct IV values are returned to callers, thereby restoring the intended security properties of the encryption process.