CVE-2020-11728 in Andrew's Web Libraries
Summary
by MITRE
An issue was discovered in DAViCal Andrew's Web Libraries (AWL) through 0.60. Session management does not use a sufficiently hard-to-guess session key. Anyone who can guess the microsecond time (and the incrementing session_id) can impersonate a session.
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Analysis
by VulDB Data Team • 05/27/2024
The vulnerability identified as CVE-2020-11728 affects DAViCal Andrew's Web Libraries version 0.60 and earlier, representing a critical session management flaw that undermines the security of web applications relying on this component. This weakness stems from insufficient entropy in session key generation, creating predictable session identifiers that can be exploited by malicious actors to gain unauthorized access to user sessions. The vulnerability specifically targets the session management mechanism within the AWL framework, which is widely used in calendar and scheduling applications that require robust authentication and session handling capabilities.
The technical flaw manifests in the predictable nature of session identifiers generated by the DAViCal AWL library, where session keys are derived from microsecond timestamps combined with incrementing session_id values. This approach creates a significant attack surface because the time component can be easily guessed or brute-forced, particularly when attackers have knowledge of the application's operational timing or can observe session creation patterns. The predictability arises from the lack of sufficient randomness in the session key generation algorithm, making it feasible for an attacker to compute valid session tokens without requiring authentication credentials. This vulnerability directly maps to CWE-330, which addresses the use of insufficiently random values in security contexts, and represents a clear violation of secure session management principles outlined in industry standards such as NIST SP 800-63B.
The operational impact of this vulnerability extends beyond simple unauthorized access, as it enables session hijacking attacks that can result in complete compromise of user accounts and sensitive calendar data. Attackers can leverage the predictable session keys to impersonate legitimate users, potentially gaining access to personal schedules, shared calendar events, and other calendaring information that may contain confidential business or personal details. The attack vector is particularly concerning because it does not require complex exploitation techniques or privileged access to the system, making it accessible to threat actors with basic knowledge of web application vulnerabilities. This weakness can be exploited in various attack scenarios including man-in-the-middle attacks, session fixation, or simple brute-force attempts against predictable session identifiers, all of which can lead to unauthorized data access and potential data manipulation within the affected applications.
Mitigation strategies for this vulnerability should focus on implementing robust session key generation mechanisms that incorporate sufficient entropy and randomness to prevent predictability. Organizations should immediately upgrade to DAViCal AWL version 0.61 or later, where the session management has been enhanced to use cryptographically secure random number generators for session identifier creation. Additionally, security measures should include implementing proper session timeout mechanisms, using secure session cookies with appropriate flags, and ensuring that session identifiers are sufficiently long and random to prevent guessing attacks. The remediation approach aligns with ATT&CK technique T1548.003, which addresses the exploitation of weak session management, and should be complemented with network monitoring to detect suspicious session-related activities. Organizations should also consider implementing additional authentication layers such as multi-factor authentication to provide defense-in-depth against session-based attacks, while ensuring that all applications using this library are properly updated and that session management configurations follow security best practices recommended by OWASP and other industry security frameworks.