CVE-2024-31995 in zcap
Summary
by MITRE • 04/11/2024
`@digitalbazaar/zcap` provides JavaScript reference implementation for Authorization Capabilities. Prior to version 9.0.1, when invoking a capability with a chain depth of 2, i.e., it is delegated directly from the root capability, the `expires` property is not properly checked against the current date or other `date` param. This can allow invocations outside of the original intended time period. A zcap still cannot be invoked without being able to use the associated private key material. `@digitalbazaar/zcap` v9.0.1 fixes expiration checking. As a workaround, one may revoke a zcap at any time.
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Analysis
by VulDB Data Team • 05/16/2024
The vulnerability identified as CVE-2024-31995 affects the @digitalbazaar/zcap JavaScript library which implements Authorization Capabilities for decentralized identity systems. This library serves as a reference implementation for managing capabilities that grant specific permissions within distributed systems. The flaw exists in versions prior to 9.0.1 and specifically impacts the validation of expiration timestamps when capabilities are invoked with a chain depth of exactly two levels. The vulnerability represents a temporal authorization bypass that could permit unauthorized use of capabilities beyond their intended time windows.
The technical implementation flaw stems from inadequate validation of the expires property within the capability invocation process. When a capability is delegated directly from a root capability, the system fails to properly compare the expiration timestamp against the current system time or other temporal parameters. This validation gap creates a window where capabilities can be legitimately invoked even after their designated expiration time has passed. The vulnerability is particularly concerning because it operates at the delegation level where the chain depth equals two, indicating a specific pattern in capability delegation that was not adequately protected. The root cause aligns with CWE-605, which addresses "Double Check" and "Race Condition" vulnerabilities in authorization systems, specifically when temporal constraints are not properly enforced during access control validation.
The operational impact of this vulnerability extends beyond simple time-based authorization bypasses. While the system correctly requires possession of the associated private key material for invocation, the expiration check failure creates a scenario where authorized parties could potentially exploit capabilities for longer periods than intended. This temporal malleability could lead to extended access windows that might be exploited by malicious actors who have legitimate access to the capability but not necessarily the private key. The vulnerability affects systems that rely on time-bound capabilities for security enforcement, potentially undermining trust models where temporal constraints are critical for access control. Organizations using this library in production environments may experience unauthorized access to resources that should have expired, particularly in scenarios where capability delegation chains are commonly two levels deep.
Mitigation strategies for CVE-2024-31995 include immediate upgrade to version 9.0.1 or later of the @digitalbazaar/zcap library, which contains the fixed expiration checking functionality. The library developers have addressed this issue by implementing proper temporal validation that compares the expires property against current time parameters. As a temporary workaround, administrators can revoke affected capabilities at any time to prevent further unauthorized use, though this requires maintaining capability revocation mechanisms. Organizations should conduct thorough audits of their capability usage patterns to identify instances where delegation chains might be two levels deep and where temporal constraints are critical for security. This vulnerability demonstrates the importance of comprehensive temporal validation in distributed authorization systems and aligns with ATT&CK techniques related to privilege escalation through authorization bypasses, particularly in the context of capability-based security models where time-based constraints are fundamental to access control enforcement.