CVE-2023-42816 in Kyverno
Summary
by MITRE • 11/13/2023
Kyverno is a policy engine designed for Kubernetes. A security vulnerability was found in Kyverno where an attacker could cause denial of service of Kyverno. The vulnerability was in Kyvernos Notary verifier. An attacker would need control over the registry from which Kyverno would fetch signatures. With such a position, the attacker could return a malicious response to Kyverno, when Kyverno would send a request to the registry. The malicious response would cause denial of service of Kyverno, such that other users' admission requests would be blocked from being processed. This is a vulnerability in a new component released in v1.11.0. The only users affected by this are those that have been building Kyverno from source at the main branch which is not encouraged. Users consuming official Kyverno releases are not affected. There are no known cases of this vulnerability being exploited in the wild.
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Analysis
by VulDB Data Team • 12/06/2023
CVE-2023-42816 represents a denial of service vulnerability within Kyverno's Notary verifier component, specifically affecting versions prior to the official release that includes the patched functionality. This vulnerability stems from insufficient input validation and response handling when Kyverno interacts with container registries during signature verification processes. The flaw exists in the Notary verifier module that was introduced in version 1.11.0, making it a relatively new attack surface that has not yet been widely exploited in production environments. The vulnerability manifests when Kyverno attempts to fetch cryptographic signatures from container registries, creating a potential attack vector for adversaries who have compromised access to the registry infrastructure. The technical implementation involves improper handling of registry responses that could contain malformed or malicious data structures, leading to resource exhaustion or process termination within the Kyverno admission controller. This weakness directly relates to CWE-400, which categorizes improper handling of resource consumption, and aligns with ATT&CK technique T1499.004, which covers network denial of service attacks targeting infrastructure components. The impact of this vulnerability extends beyond simple service disruption as it affects the core admission control functionality of Kubernetes clusters, potentially blocking legitimate admission requests from being processed and thereby compromising cluster security posture. The vulnerability's exploitation requires an attacker to have control over the registry from which Kyverno fetches signatures, making it a privilege escalation scenario rather than a straightforward network-based attack. This dependency on registry compromise means the attack surface is limited to environments where such access has already been established through other means. Organizations using official Kyverno releases are protected from this vulnerability since the patched version has been included in stable distributions. The issue primarily affects developers and security teams who have been building Kyverno from the main branch source code, which is not the recommended practice for production environments. The vulnerability's classification as a denial of service weakness in a security tool creates a particularly concerning scenario where an attacker could potentially disrupt cluster operations while maintaining access to the system. This makes the vulnerability particularly dangerous in environments where Kyverno is used as a critical admission control mechanism for enforcing security policies. The remediation approach focuses on upgrading to official releases that include the patched Notary verifier component, ensuring that users are not running code from unstable development branches. Organizations should also implement monitoring for unusual registry behavior and consider network segmentation to limit potential attack vectors. The vulnerability demonstrates the importance of validating external dependencies and implementing proper input sanitization in security-critical components, particularly those that interact with external systems such as container registries. This weakness highlights the need for comprehensive testing of new components before they are included in production releases, especially in security tools where reliability and availability are paramount for maintaining cluster integrity. The absence of known exploitation attempts in the wild suggests that this vulnerability may be relatively complex to exploit successfully, but the potential impact on cluster operations makes it a critical concern for security administrators.