CVE-2024-42473 in OpenFGA
Summary
by MITRE • 08/12/2024
OpenFGA is an authorization/permission engine. OpenFGA v1.5.7 and v1.5.8 are vulnerable to authorization bypass when calling Check API with a model that uses `but not` and `from` expressions and a userset. Users should downgrade to v1.5.6 as soon as possible. This downgrade is backward compatible. As of time of publication, a patch is not available but OpenFGA's maintainers are planning a patch for inclusion in a future release.
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Analysis
by VulDB Data Team • 10/01/2024
The vulnerability identified as CVE-2024-42473 affects OpenFGA, an authorization and permission engine designed to manage complex access control policies. This authorization bypass flaw specifically manifests when the Check API is invoked with a model that incorporates `but not` and `from` expressions in conjunction with usersets. The affected versions include OpenFGA v1.5.7 and v1.5.8, while v1.5.6 remains unaffected and is recommended as a temporary downgrade solution. This issue represents a significant security concern as it allows unauthorized access to resources that should be restricted based on the defined authorization policies.
The technical flaw stems from improper handling of authorization logic when processing `but not` and `from` expressions within the Check API implementation. These expressions create complex permission rules where certain users or groups are explicitly excluded from access (`but not`) while simultaneously establishing relationships through usersets (`from`). The vulnerability occurs when the system fails to properly evaluate these combined expressions, leading to situations where users who should be denied access can bypass restrictions and gain unauthorized permissions. This represents a weakness in the authorization engine's logical evaluation process and demonstrates a failure in proper access control enforcement mechanisms.
The operational impact of this vulnerability is substantial as it directly compromises the integrity of the authorization system. An attacker who can manipulate API calls to the Check endpoint with the specific combination of `but not` and `from` expressions could potentially access resources that should be restricted to authorized users only. This bypass allows for privilege escalation and unauthorized data access, potentially affecting sensitive information and system resources. The vulnerability affects any organization using OpenFGA with policies that utilize these specific expression types, making it a critical concern for systems implementing complex access control policies.
Organizations should immediately implement the recommended mitigation by downgrading to OpenFGA v1.5.6, which maintains backward compatibility with existing configurations and policies. This downgrade approach ensures that systems remain protected while awaiting the official patch from OpenFGA maintainers. Security teams should conduct thorough audits of their authorization policies to identify any usage of `but not` and `from` expressions that might be vulnerable to this bypass. Additionally, monitoring systems should be enhanced to detect unusual API access patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-284 (Improper Access Control) and could potentially be leveraged in techniques categorized under ATT&CK tactic TA0004 (Privilege Escalation) and TA0006 (Credential Access) depending on the specific implementation and target resources. Organizations should also consider implementing additional security controls such as API rate limiting and enhanced logging to detect potential exploitation attempts while awaiting the formal patch release.