CVE-2023-5978 in FreeBSD
Summary
by MITRE • 11/08/2023
In versions of FreeBSD 13-RELEASE before 13-RELEASE-p5, under certain circumstances the cap_net libcasper(3) service incorrectly validates that updated constraints are strictly subsets of the active constraints. When only a list of resolvable domain names was specified without setting any other limitations, an application could submit a new list of domains including include entries not previously listed. This could permit the application to resolve domain names that were previously restricted.
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Analysis
by VulDB Data Team • 12/05/2023
The vulnerability identified as CVE-2023-5978 affects FreeBSD 13-RELEASE versions prior to 13-RELEASE-p5 and represents a significant flaw in the network capability validation mechanism within the libcasper(3) service. This issue resides in the cap_net capability management system that controls network access permissions for applications running on FreeBSD systems. The problem manifests when applications attempt to update network constraints through the casper service, specifically when dealing with domain name resolution restrictions. The flaw stems from an incorrect validation algorithm that fails to properly enforce the subset relationship between old and new constraint sets, creating a potential security bypass mechanism.
The technical implementation of this vulnerability involves the cap_net libcasper service maintaining a set of active network constraints that limit what domain names an application can resolve. When an application submits a new constraint list containing domain names, the service should verify that all new entries are strictly contained within the previously active constraint set. However, the validation logic incorrectly allows new domain entries to be added to the constraint list even when those entries were not part of the original active constraints. This occurs specifically when only a list of resolvable domain names is provided without additional limiting parameters, effectively creating a scenario where applications can expand their network access privileges beyond the originally intended scope.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass potential data exfiltration and network reconnaissance capabilities. An application that previously had restricted domain resolution access could exploit this flaw to resolve additional domain names that were not permitted in the original constraint set, potentially enabling access to sensitive resources or systems that should have been blocked. This vulnerability particularly affects systems where network access controls are strictly enforced through the casper service, creating opportunities for attackers to bypass security policies that should prevent unauthorized network communication. The flaw represents a classic case of insufficient input validation and privilege management that could be exploited in various attack scenarios.
Mitigation strategies for CVE-2023-5978 should prioritize immediate system updates to FreeBSD 13-RELEASE-p5 or later versions where the validation logic has been corrected. Organizations should also implement additional monitoring of casper service usage and constraint modifications to detect potential exploitation attempts. Security teams should review existing network access control policies and validate that applications are not unnecessarily granted broad domain resolution capabilities. The vulnerability aligns with CWE-284 Access Control Issues and can be categorized under ATT&CK technique T1068, which addresses local privilege escalation through system configuration vulnerabilities. Additionally, this flaw demonstrates the importance of proper constraint validation in capability-based security systems and underscores the critical need for thorough testing of privilege management mechanisms in operating system security frameworks.