CVE-2015-7824 in Botan
Summary
by MITRE
botan 1.11.x before 1.11.22 makes it easier for remote attackers to decrypt TLS ciphertext data via a padding-oracle attack against TLS CBC ciphersuites.
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Analysis
by VulDB Data Team • 08/28/2020
The vulnerability identified as CVE-2015-7824 affects the Botan cryptographic library version 1.11.x prior to 1.11.22, specifically targeting the implementation of TLS CBC ciphersuites. This issue represents a significant security weakness that directly impacts the confidentiality of encrypted communications. The flaw manifests as a padding-oracle attack vulnerability that allows remote adversaries to systematically decrypt TLS ciphertext data without possessing the necessary cryptographic keys or session information.
The technical nature of this vulnerability stems from improper handling of padding validation during the TLS decryption process. When processing TLS records with CBC (Cipher Block Chaining) encryption, the library fails to implement constant-time padding verification mechanisms. This timing discrepancy creates observable differences in response behavior that attackers can exploit through statistical analysis and repeated requests. The vulnerability specifically affects the TLS protocol implementation within Botan, where the padding validation process reveals information about the validity of padding bytes, enabling attackers to perform iterative decryption attempts.
From an operational perspective, this vulnerability poses a substantial risk to any system relying on Botan for TLS encryption services. Remote attackers can leverage this weakness to decrypt sensitive data transmitted over TLS connections, potentially exposing confidential information including authentication credentials, personal data, financial records, and proprietary business information. The attack requires only network access to the vulnerable service and can be automated to systematically recover encrypted payloads over time. The impact extends beyond simple data theft to potential authentication bypass scenarios and privilege escalation attacks when sensitive session information is compromised.
The vulnerability aligns with CWE-209, which addresses "Information Exposure Through an Error Message," and demonstrates characteristics consistent with the ATT&CK technique T1566.001 for credential access through network-based attacks. Organizations utilizing Botan versions 1.11.x before 1.11.22 should immediately implement mitigation strategies including upgrading to the patched version 1.11.22 or later, disabling CBC ciphersuites in favor of more secure AEAD modes, and implementing additional monitoring for suspicious network activity patterns. Security teams should also consider deploying intrusion detection systems capable of identifying padding oracle attack patterns and establishing incident response procedures to address potential compromise scenarios. The fix implemented in version 1.11.22 includes proper constant-time padding validation and improved error handling to prevent information leakage during TLS decryption operations.