CVE-2015-7827 in Botan
Summary
by MITRE
Botan before 1.10.13 and 1.11.x before 1.11.22 makes it easier for remote attackers to conduct million-message attacks by measuring time differences, related to decoding of PKCS#1 padding.
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Analysis
by VulDB Data Team • 08/19/2022
The vulnerability identified as CVE-2015-7827 affects the Botan cryptographic library, specifically versions prior to 1.10.13 and 1.11.x versions before 1.11.22. This weakness stems from insufficient timing protection during the decoding process of PKCS#1 padding, creating a side-channel attack vector that significantly weakens the security of cryptographic operations. The issue is particularly concerning because it enables remote adversaries to conduct million-message attacks through precise measurement of time differences, fundamentally undermining the security assumptions of the cryptographic system.
The technical flaw manifests in the cryptographic library's handling of PKCS#1 padding decoding operations. When processing encrypted messages that utilize PKCS#1 padding, the library exhibits variable timing behavior that correlates with the validity of padding structures. This timing variation occurs because the implementation does not employ constant-time operations during the padding validation process, allowing attackers to observe and measure the time differences between valid and invalid padding attempts. The vulnerability directly relates to CWE-203, which describes "Observable Timing Discrepancy" in cryptographic implementations, where timing variations can leak information about the internal state of cryptographic operations.
The operational impact of this vulnerability is severe as it enables sophisticated side-channel attacks that can compromise the security of RSA-based cryptographic operations. Attackers can leverage this timing information to perform million-message attacks, where they systematically send numerous encrypted messages to a target system and analyze the timing variations to deduce information about the private key or the encryption process. This type of attack falls under the ATT&CK technique T1059.001, which covers "Command and Scripting Interpreter: Python" in the context of automated attack automation, though the specific vulnerability relates more directly to cryptographic side-channel analysis techniques. The vulnerability essentially provides an attacker with a powerful information leakage mechanism that can be exploited to reduce the computational complexity of breaking RSA encryption.
The implications extend beyond simple timing attacks to encompass broader cryptographic security weaknesses in the library's implementation. When cryptographic libraries fail to provide constant-time operations, they become susceptible to various side-channel attacks that can systematically weaken encryption strength over time. This vulnerability represents a critical failure in the security design principles that cryptographic implementations must follow, particularly in the area of resistance to timing-based attacks. The attack vector is particularly dangerous because it requires minimal privileges and can be executed remotely, making it accessible to a wide range of threat actors. Organizations using affected versions of the Botan library should immediately implement mitigations including upgrading to patched versions, implementing constant-time cryptographic operations, and considering additional protections such as timing randomization or hardware security modules to prevent exploitation of this timing vulnerability.