CVE-2026-74871 in openssl_encrypt
Summary
by MITRE • 08/17/2026
openssl_encrypt versions before 1.4.6 contain a key derivation flaw in sequential XOR composition mode where the last stage cancels out during key generation. When configured with a single KDF and no prior hashing stage, attackers can bypass memory-hard key derivation and perform offline password cracking at SHA-256 speed instead of the configured KDF cost.
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Analysis
by VulDB Data Team • 08/17/2026
The vulnerability identified in OpenSSL_encrypt versions preceding 1.4.6 represents a critical flaw within the implementation of sequential XOR composition modes used for key derivation functions. This specific defect arises from an arithmetic error during the final stage of the key generation process, where the last operational step effectively cancels out previous computations rather than contributing to them as intended. In cryptographic systems that rely on iterative processes to derive secure keys from passwords or secrets, each stage is designed to add complexity and computational cost, thereby increasing the difficulty for an attacker attempting to reverse-engineer the original input. However, due to this implementation error, the final XOR operation nullifies the work performed by earlier stages when specific configuration conditions are met. This mathematical anomaly fundamentally undermines the security model of the key derivation function, reducing what should be a computationally expensive process into a significantly weaker one that fails to provide adequate protection against brute-force attacks.
The operational impact of this vulnerability is severe for applications relying on memory-hard or cost-adjusted key derivation algorithms without an preceding hashing stage. When configured with a single Key Derivation Function and no prior hashing step, the system becomes susceptible to offline password cracking at speeds comparable to SHA-256 computations rather than adhering to the intended higher computational cost of the KDF. This discrepancy allows attackers who have obtained encrypted data or hashed credentials to perform dictionary attacks or brute-force attempts with vastly increased efficiency. The loss of memory-hardness and reduced iteration costs means that modern GPU clusters can test millions of password guesses per second, drastically reducing the time required to compromise user accounts or decrypt sensitive information protected by these keys. This effectively renders the configured security parameters obsolete, leaving systems exposed to rapid credential theft even if strong passwords are used initially.
From a classification perspective, this vulnerability aligns with CWE-347 Improper Verification of Cryptographic Signature and CWE-695 Use of Low-Level Primitives in an Insecure Manner, as it involves the incorrect application of low-level cryptographic operations leading to weakened security properties. It also relates to CWE-208 Observable Timing Discrepancy if the cancellation effect introduces measurable differences in processing time that could be exploited for side-channel analysis, although the primary concern remains the drastic reduction in computational cost. In terms of the MITRE ATT&CK framework, this flaw facilitates techniques associated with T1110 Brute Force and specifically impacts the defense against offline credential cracking by lowering the barrier to entry for attackers. The vulnerability highlights the importance of rigorous code review and formal verification in cryptographic libraries, as subtle logical errors can have catastrophic consequences for data confidentiality and integrity.
Mitigation strategies must prioritize immediate upgrading to OpenSSL_encrypt version 1.4.6 or later, where this key derivation flaw has been corrected by developers through proper implementation of the sequential XOR composition logic. For systems that cannot be immediately updated due to dependency constraints, temporary mitigations should include enforcing a prior hashing stage before applying the KDF, which alters the input state and prevents the cancellation effect from occurring in its current form. Additionally, organizations should review their cryptographic configurations to ensure they are not relying solely on single-stage key derivation without additional layers of security such as salting or pre-hashing. Regular audits of password storage mechanisms and encryption implementations are essential to detect similar logical flaws before they can be exploited. Security teams must also monitor for any emerging exploits targeting this specific version range and apply patches promptly across all affected environments to maintain the integrity of stored credentials and encrypted data.