CVE-2010-3075 in EncFS
Summary
by MITRE
EncFS before 1.7.0 encrypts multiple blocks by means of the CFB cipher mode with the same initialization vector, which makes it easier for local users to obtain sensitive information via calculations involving recovery of XORed data, as demonstrated by an attack on encrypted data in which the last block contains only one byte.
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Analysis
by VulDB Data Team • 09/25/2021
The vulnerability identified as CVE-2010-3075 affects EncFS versions prior to 1.7.0 and represents a critical cryptographic flaw that undermines the security of encrypted data storage. This issue stems from the improper implementation of the Cipher Feedback (CFB) mode of operation, where the same initialization vector is reused across multiple encryption operations. The vulnerability is classified under CWE-327, which specifically addresses the use of insecure cryptographic algorithms and modes of operation, making it particularly dangerous for applications that rely on proper encryption practices. The flaw allows attackers to exploit the deterministic nature of the encryption process and recover sensitive information through mathematical analysis of the encrypted data.
The technical implementation of this vulnerability occurs when EncFS processes multiple blocks of data using CFB mode with identical initialization vectors, creating predictable patterns in the encrypted output. When an attacker can identify or guess the content of one block, they can perform XOR operations between corresponding blocks of encrypted data to reveal information about the plaintext. The specific attack scenario mentioned in the vulnerability description demonstrates how an attacker can recover information from encrypted data when the final block contains only a single byte, making the vulnerability particularly exploitable in practical scenarios. This weakness is rooted in fundamental cryptographic principles where the reuse of initialization vectors in stream cipher modes creates vulnerabilities that can be leveraged through cryptanalysis techniques.
The operational impact of this vulnerability extends beyond simple information disclosure, as it creates opportunities for attackers to reconstruct portions of the original data without requiring brute force attacks or key recovery. Local users who have access to the encrypted filesystem can exploit this weakness to determine patterns in the data, potentially leading to full data recovery in certain circumstances. The attack vector is particularly concerning because it does not require sophisticated tools or extensive computational resources, making it accessible to attackers with basic cryptographic knowledge. This vulnerability significantly weakens the security posture of systems relying on EncFS for data protection and can result in unauthorized access to sensitive information stored in encrypted volumes.
Mitigation strategies for this vulnerability require immediate upgrading to EncFS version 1.7.0 or later, where the implementation properly handles initialization vector generation and ensures that each encryption operation uses a unique initialization vector. Organizations should also implement regular security audits of their encryption implementations and ensure that cryptographic libraries are kept up to date with the latest security patches. The remediation process involves not only updating the software but also potentially re-encrypting existing data to ensure that previously compromised data cannot be exploited. Security teams should monitor for similar vulnerabilities in other cryptographic implementations and consider adopting more robust encryption modes such as Galois/Counter Mode (GCM) or Cipher Block Chaining (CBC) with proper initialization vector handling as recommended by NIST standards and the ATT&CK framework for cryptographic operations.