CVE-2004-2136 in Linux
Summary
by MITRE
dm-crypt on Linux kernel 2.6.x, when used on certain file systems with a block size 1024 or greater, has certain "IV computation" weaknesses that allow watermarked files to be detected without decryption.
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Analysis
by VulDB Data Team • 04/13/2019
The vulnerability identified as CVE-2004-2136 represents a significant cryptographic weakness in the Linux kernel's dm-crypt implementation that affects versions 2.6.x and later. This flaw specifically manifests when dm-crypt is deployed on file systems that utilize block sizes of 1024 bytes or greater, creating a scenario where the initialization vector computation process becomes predictable and exploitable. The vulnerability stems from the deterministic nature of how initialization vectors are calculated within the encryption process, which violates fundamental cryptographic principles that require randomness and unpredictability in cryptographic operations. According to the CWE classification system, this represents a weakness in cryptographic implementation under CWE-327, specifically related to the use of insecure or weak cryptographic algorithms and implementation practices that compromise the confidentiality and integrity of encrypted data.
The technical flaw in dm-crypt's IV computation mechanism allows attackers to identify watermarked files through analysis of the encryption patterns without possessing the decryption keys. This occurs because the initialization vectors are derived from predictable patterns based on file system block positions rather than being properly randomized for each encryption operation. When file systems with large block sizes are used, the mathematical relationship between the block addresses and the computed initialization vectors becomes apparent to an attacker who can analyze the encrypted data structure. The vulnerability creates a side-channel attack vector that enables detection of watermarking within encrypted files, essentially undermining the security assumptions that encrypted data should remain opaque to unauthorized parties. This weakness is particularly concerning as it operates at the kernel level and affects the core encryption mechanisms that protect data at rest, making it a critical vulnerability for systems handling sensitive information.
The operational impact of this vulnerability extends beyond simple information disclosure, as it fundamentally compromises the security model of dm-crypt encryption. Attackers can exploit this weakness to determine whether specific files contain watermarks or other embedded identifiers, which can reveal information about file contents, user activities, or system configurations without actually decrypting the data. This capability has implications for privacy protection, as it allows for passive monitoring and analysis of encrypted data streams. The vulnerability also impacts compliance with various security standards that require strong encryption guarantees, particularly in environments where data confidentiality is paramount. Organizations using dm-crypt for data protection may inadvertently expose metadata about their file systems and data structures, creating potential attack vectors for adversaries seeking to understand system configurations or identify specific file types within encrypted volumes. According to ATT&CK framework, this vulnerability maps to T1566 (Phishing for Information) and T1552 (Unsecured Credentials) as it enables adversaries to gather intelligence about encrypted data without direct access to encryption keys or credentials.
Mitigation strategies for CVE-2004-2136 require immediate attention from system administrators and security teams responsible for Linux systems utilizing dm-crypt encryption. The primary recommendation involves upgrading to newer kernel versions where this vulnerability has been addressed through improved IV computation algorithms that ensure proper randomization of initialization vectors. Organizations should also consider implementing alternative encryption solutions that do not suffer from similar IV computation weaknesses, particularly when dealing with large block size file systems. Additionally, system administrators should conduct comprehensive audits of their encryption implementations to identify any instances where dm-crypt is deployed with block sizes of 1024 bytes or greater, as these configurations are particularly vulnerable to exploitation. The remediation process should include thorough testing of updated kernel versions to ensure compatibility with existing systems while maintaining security integrity. Organizations should also implement monitoring solutions that can detect anomalous patterns in encrypted file access that might indicate exploitation attempts targeting this vulnerability. Proper configuration management and regular security assessments are essential to prevent unauthorized access to encrypted data through this and similar cryptographic weaknesses that compromise the fundamental security guarantees of encryption technologies.