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CVE-2021-25735 is an authorization bypass in Kubernetes kube-apiserver affecting validation of Node update requests. Under specific conditions, a Node update can bypass a Validating Admission Webhook when that webhook's denial decision depends at least partly on the prior state of the Node object. Some previous Node fields are not observed by the webhook, allowing an update that should have been rejected under old-state-aware validation logic to be admitted.
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1 valid exploit after Mallory filtered fakes, detection scripts, and README-only repos.
This repository is a proof-of-concept (POC) exploit for CVE-2021-25735, a vulnerability in Kubernetes' validating admission webhooks. The repository contains a Node.js application (app/server.js) that acts as a validating admission webhook, deployed via Kubernetes manifests (webhook-deploy.yaml and webhook-registration.yaml). The exploit demonstrates how an attacker can bypass the webhook's validation logic by manipulating the 'changeAllowed' label in node metadata. The provided bash script (gencerts.sh) generates the necessary TLS certificates for secure webhook communication. The README.md provides step-by-step instructions for setting up the vulnerable environment and reproducing the exploit. The main attack vector is network-based, as the exploit targets the Kubernetes API server's webhook mechanism. The repository is structured for educational and demonstration purposes, not for weaponization.
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