CVE-2018-16398 in AuthZ Broker
Summary
by MITRE
In Twistlock AuthZ Broker 0.1, regular expressions are mishandled, as demonstrated by containers/aa/pause?aaa=\/start to bypass a policy in which "docker start" is allowed but "docker pause" is not allowed.
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Analysis
by VulDB Data Team • 05/06/2023
The vulnerability identified as CVE-2018-16398 resides within the Twistlock AuthZ Broker version 0.1, a security component designed to enforce authorization policies for containerized environments. This flaw represents a critical weakness in the policy enforcement mechanism that governs container operations, specifically affecting how regular expressions are processed within the authorization framework. The issue manifests when the system fails to properly validate or sanitize regular expression patterns used in policy definitions, creating a path for malicious actors to bypass intended security controls. The vulnerability demonstrates a classic case of improper input validation where user-supplied data containing regular expressions can be manipulated to evade security restrictions, directly impacting the integrity of container orchestration policies.
The technical implementation of this vulnerability exploits a flaw in the regular expression handling logic that processes policy enforcement rules. When a user submits a request containing a specially crafted regular expression pattern, the system fails to properly interpret or validate the pattern against established security policies. In the specific example provided, the payload containers/aa/pause?aaa=\/start demonstrates how an attacker can manipulate the request structure to bypass a policy that permits "docker start" operations while blocking "docker pause" commands. This occurs because the regular expression engine processes the input in a manner that allows the bypassed operation to match against the allowed pattern, effectively circumventing the intended access control restrictions. The vulnerability stems from inadequate sanitization of user input and improper handling of special characters within regular expression contexts, creating a path for privilege escalation through policy evasion.
The operational impact of this vulnerability extends beyond simple policy bypass, as it fundamentally undermines the security posture of containerized environments that rely on Twistlock AuthZ Broker for access control. Organizations using this component face significant risk of unauthorized container operations, potentially allowing attackers to execute privileged commands that should be restricted. The vulnerability enables attackers to perform operations such as pausing containers, which could be used for data exfiltration, system disruption, or as a stepping stone for further compromise. This weakness directly violates the principle of least privilege and can lead to complete container orchestration system compromise. The implications are particularly severe in multi-tenant environments where proper isolation between container operations is critical for maintaining security boundaries and preventing lateral movement attacks.
Mitigation strategies for CVE-2018-16398 should focus on immediate patching of the Twistlock AuthZ Broker component to address the regular expression handling flaw. Organizations must also implement additional input validation measures to sanitize all user-supplied data before it reaches the regular expression processing engine. Security teams should review and audit existing authorization policies to identify potential bypass opportunities and ensure that regular expression patterns are properly escaped and validated. The vulnerability aligns with CWE-20, which addresses improper input validation, and reflects patterns commonly seen in attack vectors categorized under the MITRE ATT&CK framework's privilege escalation techniques. Organizations should consider implementing network segmentation and monitoring for anomalous container operations that may indicate exploitation attempts, while also ensuring that all container security tools are kept up to date with the latest security patches to prevent similar vulnerabilities from being exploited in the future.