CVE-2021-39159 in BinderHub
Summary
by MITRE • 08/25/2021
BinderHub is a kubernetes-based cloud service that allows users to share reproducible interactive computing environments from code repositories. In affected versions a remote code execution vulnerability has been identified in BinderHub, where providing BinderHub with maliciously crafted input could execute code in the BinderHub context, with the potential to egress credentials of the BinderHub deployment, including JupyterHub API tokens, kubernetes service accounts, and docker registry credentials. This may provide the ability to manipulate images and other user created pods in the deployment, with the potential to escalate to the host depending on the underlying kubernetes configuration. Users are advised to update to version 0.2.0-n653. If users are unable to update they may disable the git repo provider by specifying the `BinderHub.repo_providers` as a workaround.
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Analysis
by VulDB Data Team • 08/29/2021
CVE-2021-39159 represents a critical remote code execution vulnerability within BinderHub, a Kubernetes-based platform designed to facilitate reproducible interactive computing environments through code repositories. This vulnerability stems from insufficient input validation mechanisms within the BinderHub service, specifically when processing user-provided repository information. The flaw allows attackers to inject maliciously crafted inputs that can trigger code execution within the BinderHub operational context, effectively creating a pathway for privilege escalation and credential exfiltration. The vulnerability is categorized under CWE-20, which addresses improper input validation, and aligns with ATT&CK technique T1059.001 for command and script injection, demonstrating how unvalidated inputs can be leveraged for arbitrary code execution.
The security implications of this vulnerability extend beyond simple code execution, as the compromised BinderHub instance gains access to sensitive credentials including JupyterHub API tokens, Kubernetes service account credentials, and Docker registry authentication details. These credentials represent a significant attack surface since they provide access to the underlying Kubernetes cluster and associated resources. The vulnerability enables attackers to manipulate container images and user-created pods within the deployment, potentially allowing for lateral movement and privilege escalation. The risk assessment indicates that depending on the Kubernetes cluster configuration, attackers might even achieve host-level compromise, making this vulnerability particularly dangerous in production environments where proper security boundaries are not established.
The technical exploitation of this vulnerability requires an attacker to craft malicious inputs that bypass existing validation checks within the BinderHub service. This typically involves manipulating repository URLs or configuration parameters in ways that trigger the underlying code execution path. The vulnerability affects specific versions of BinderHub prior to 0.2.0-n653, making version updates the primary recommended mitigation strategy. Organizations that cannot immediately upgrade can implement a temporary workaround by disabling the git repository provider through configuration settings, specifically by setting `BinderHub.repo_providers` to prevent the vulnerable code path from being triggered. This mitigation approach aligns with defensive cybersecurity practices that focus on reducing attack surface while maintaining operational functionality. The vulnerability highlights the importance of secure input handling in cloud-native applications and demonstrates how seemingly benign repository management features can become attack vectors when proper validation mechanisms are absent. Security teams should monitor for exploitation attempts and ensure proper network segmentation to limit potential damage from successful attacks.