CVE-2013-1895 in py-bcrypt
Summary
by MITRE
The py-bcrypt module before 0.3 for Python does not properly handle concurrent memory access, which allows attackers to bypass authentication via multiple authentication requests, which trigger the password hash to be overwritten.
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Analysis
by VulDB Data Team • 06/11/2024
The py-bcrypt module vulnerability identified as CVE-2013-1895 represents a critical concurrency flaw that undermines the security of password authentication systems relying on bcrypt hashing. This vulnerability specifically affects versions of the py-bcrypt module prior to 0.3 and stems from improper handling of concurrent memory access patterns during password verification operations. The flaw creates a race condition scenario where multiple simultaneous authentication requests can interfere with each other's execution, leading to potential authentication bypasses.
The technical implementation of this vulnerability resides in the module's failure to properly synchronize memory access when processing multiple concurrent authentication requests. When multiple users attempt to authenticate simultaneously against the same password hash, the underlying bcrypt implementation does not adequately protect shared memory resources. This race condition allows an attacker to manipulate the timing of authentication requests in such a way that one request can overwrite the hash data being processed by another request. The vulnerability manifests as a memory corruption issue where the password verification process becomes unreliable due to concurrent access to the same hash storage locations.
From an operational perspective, this vulnerability presents a significant risk to authentication systems that depend on bcrypt for password hashing, particularly in multi-threaded or high-concurrency environments. Attackers can exploit this weakness by crafting multiple simultaneous authentication requests that exploit the race condition to bypass password verification entirely. The impact extends beyond simple authentication bypass to potentially allow unauthorized access to protected systems, as the compromised authentication mechanism fails to properly validate user credentials. This vulnerability is particularly dangerous in web applications and services where concurrent user access is common and where bcrypt is used for password storage and verification.
The vulnerability maps directly to CWE-367, which addresses Time-of-Check to Time-of-Use (TOCTOU) race conditions, and aligns with ATT&CK technique T1110.003 for credential access through brute force methods. The attack vector leverages concurrent processing weaknesses to create a scenario where legitimate authentication attempts can be subverted by exploiting the timing window between hash validation and memory access synchronization. Organizations using affected py-bcrypt versions should prioritize immediate patching to address this concurrency issue. Recommended mitigations include upgrading to py-bcrypt version 0.3 or later, implementing proper thread synchronization mechanisms, and conducting thorough security assessments of authentication systems that rely on bcrypt implementations. Additionally, system administrators should monitor for potential exploitation attempts and implement additional authentication controls to reduce the attack surface while patches are deployed.