CVE-2003-0078 in OpenSSL
Summary
by MITRE
ssl3_get_record in s3_pkt.c for OpenSSL before 0.9.7a and 0.9.6 before 0.9.6i does not perform a MAC computation if an incorrect block cipher padding is used, which causes an information leak (timing discrepancy) that may make it easier to launch cryptographic attacks that rely on distinguishing between padding and MAC verification errors, possibly leading to extraction of the original plaintext, aka the "Vaudenay timing attack."
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Analysis
by VulDB Data Team • 08/25/2025
The vulnerability described in CVE-2003-0078 represents a critical flaw in OpenSSL's SSL/TLS implementation that fundamentally undermines cryptographic security through timing-based information leakage. This issue affects OpenSSL versions prior to 0.9.7a and 0.9.6i, specifically within the ssl3_get_record function located in s3_pkt.c. The flaw stems from OpenSSL's handling of block cipher padding verification during SSL protocol processing, creating a subtle but exploitable timing discrepancy that can be leveraged by attackers to gain insights into encrypted communications.
The technical root cause of this vulnerability lies in the inconsistent error handling behavior when OpenSSL encounters invalid block cipher padding during record processing. When incorrect padding is detected, the system fails to perform the expected Message Authentication Code (MAC) computation before proceeding with the padding validation process. This creates a timing difference between the execution paths taken when padding errors occur versus when MAC verification errors occur. The timing discrepancy, though small, becomes measurable and exploitable through sophisticated timing attacks that can distinguish between these different error conditions.
This vulnerability directly enables what is known as the Vaudenay timing attack, named after its discoverer Pascal Vaudenay, which exploits timing differences to distinguish between padding errors and MAC verification failures. The attack operates by carefully measuring the time taken for cryptographic operations and correlating these measurements with the specific error conditions that occur during decryption. When the system processes records with incorrect padding, it follows a different execution path than when it encounters MAC verification failures, creating observable timing variations that can be amplified through statistical analysis.
The operational impact of CVE-2003-0078 extends beyond simple information leakage, as it provides attackers with a pathway to perform more sophisticated cryptographic attacks that can ultimately lead to plaintext recovery. This vulnerability is particularly dangerous in environments where SSL/TLS is used for securing sensitive communications, including financial transactions, healthcare data, and government communications. The timing attack can be particularly effective against protocols that use CBC mode block ciphers, as the padding validation process is a critical component of the decryption workflow that introduces predictable timing variations.
From a cybersecurity perspective, this vulnerability aligns with CWE-203, which describes "Observable Timing Discrepancy," and represents a classic example of how seemingly minor implementation details can create significant security weaknesses. The attack pattern follows principles outlined in the ATT&CK framework under T1071.004 for Application Layer Protocol: DNS, as it exploits timing characteristics that can be observed through network traffic analysis and cryptographic protocol interactions. The vulnerability demonstrates the importance of constant-time algorithm implementations, where all execution paths take the same amount of time regardless of input values, preventing attackers from inferring information through timing variations.
The mitigation strategy for CVE-2003-0078 requires immediate patching of affected OpenSSL installations to versions 0.9.7a or 0.9.6i and later, which implement proper MAC computation even when padding errors are detected. Organizations should also consider implementing additional security controls such as monitoring for unusual timing variations in cryptographic operations and ensuring that all systems handling sensitive data are regularly updated. The vulnerability underscores the critical importance of proper cryptographic implementation practices and the need for thorough security testing of cryptographic libraries to prevent timing-based side-channel attacks that can compromise even well-designed security protocols.