CVE-2019-11244 in Kubernetes
Summary
by MITRE
In Kubernetes v1.8.x-v1.14.x, schema info is cached by kubectl in the location specified by --cache-dir (defaulting to $HOME/.kube/http-cache), written with world-writeable permissions (rw-rw-rw-). If --cache-dir is specified and pointed at a different location accessible to other users/groups, the written files may be modified by other users/groups and disrupt the kubectl invocation.
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Analysis
by VulDB Data Team • 09/06/2023
The vulnerability CVE-2019-11244 represents a critical security flaw in Kubernetes versions 1.8 through 1.14 where the kubectl command-line tool improperly handles cache directory permissions. This issue stems from the default caching mechanism that stores schema information in the location specified by the --cache-dir flag, which typically defaults to $HOME/.kube/http-cache. The fundamental problem lies in the world-writeable permissions (rw-rw-rw-) assigned to these cache files, creating a significant attack surface that allows unauthorized users to modify critical components of the kubectl execution environment. The vulnerability is particularly concerning because it operates at the client-side tool level rather than the cluster itself, making it accessible to any user who can manipulate the cache directory structure.
The technical implementation of this flaw involves kubectl's caching behavior where it stores HTTP responses and schema definitions to improve performance during subsequent operations. When kubectl initializes and attempts to write cache files, it creates them with overly permissive permissions that grant write access to all users on the system. This design decision creates a privilege escalation vector where malicious users can modify these cache files to inject malicious content or manipulate the tool's behavior. The impact extends beyond simple data corruption since these cache files contain schema information that kubectl uses to validate API requests and understand cluster capabilities. When modified by unauthorized parties, these files can cause kubectl to misinterpret cluster responses, potentially leading to command execution errors or even arbitrary code execution if the cache modifications affect command parsing.
From an operational perspective, this vulnerability enables several attack vectors that align with the attack techniques documented in the MITRE ATT&CK framework under the T1059 (Command and Scripting Interpreter) and T1068 (Local Privilege Escalation) domains. An attacker with access to a shared system or the ability to create a cache directory in a world-writeable location can manipulate kubectl behavior to execute unintended commands or bypass security controls. The vulnerability is particularly dangerous in multi-user environments where users might share home directories or have access to common system locations. The impact is not limited to immediate command failures but can also result in information disclosure, as cache files might contain sensitive API response data or authentication tokens that could be extracted through manipulation of the cached content.
The security implications of this vulnerability extend beyond immediate exploitation to encompass broader system integrity concerns. According to CWE-732, this represents an inadequate permission assignment where the system grants permissions that are too broad, specifically CWE-732: "Incorrect Permission Assignment for Critical Resource." The vulnerability essentially allows for a form of cache poisoning that can disrupt legitimate kubectl operations and potentially compromise the security of the entire Kubernetes management workflow. Organizations using affected Kubernetes versions should immediately implement mitigations including restricting cache directory permissions, using dedicated cache directories with appropriate ownership, and ensuring that the --cache-dir flag points to secure locations with restricted access. Additionally, regular security audits should verify that no world-writeable cache directories exist in the system and that proper access controls are maintained across all user accounts and shared resources.