ArgoCD Vulnerable to Use of Risky or Missing Cryptographic Algorithms in Redis Cache

Summary

By default, the Redis database server is not password-protected. Consequently, an attacker with access to the Redis server can gain read/write access to the data in Redis. The attacker can also modify the "mfst" (manifest) key to cause ArgoCD to execute any deployment, potentially leveraging ArgoCD's high privileges to take over the cluster. Updating the "cacheEntryHash" in the manifest JSON is necessary, but since it doesn't use a private key for signing its integrity, a simple script can generate a new FNV64a hash matching the new manifest values. The repo-server, unable to verify if its cache is compromised, will read the altered "mfst" key and initiate an update process for the injected deployment.

It's also possible to edit the "app|resources-tree" key, causing the ArgoCD server to load any Kubernetes resource into the live manifest section of the app preview. This could lead to an information leak.

The fact that the cache in Redis is neither signed nor validated, combined with Redis's default lack of password protection, presents a significant security concern given ArgoCD's high-level permissions within the cluster. A security update should ensure all Redis database values are signed or encrypted.

Details

We began by deploying ArgoCD on an EKS cluster. Surprisingly, we discovered that an unprivileged pod in a different namespace on the same cluster could connect to the Redis server on port 6379. This was unexpected, as we had observed network policy rules restricting access to the Redis server to only the pods application-controller, repo-server, and argocd-server. We later realized that, despite having installed the latest version of the VPC CNI plugin on the EKS cluster, it requires manual enablement through configuration to enforce network policies. This raises concerns that many clients might unknowingly have open access to their Redis servers. We also know your recommendation on this page Argo CD - Secret Management, to enable the network policy plugin. Further investigation revealed that any pod within my cluster could connect to the Redis server by resolving its address using the Kubernetes DNS server. Exploring the contents of the Redis server, we found that we could edit the 'mfst' value of the latest revision. By updating the “cacheEntryHash”, we made the repo-server accept it as a legitimate cache, leading ArgoCD to apply this configuration. These tests were conducted using the default configuration, with regular ArgoCD and ArgoCD via helm deployment. This scenario presents a viable attack path, enabling any pod with access to the cluster to potentially exploit ArgoCD's high permissions and take over the cluster. We believe there is a critical need to enhance the security of the cache and its components. Given that many clients likely use ArgoCD in a plug-and-play manner, they could be exposed to significant risk. I am willing to offer assistance or answer any questions you might have.

PoC

We tested this using the latest version of ArgoCD, configured with default settings. ArgoCD was installed either by applying a YAML file or through Helm. We wrote a few Go programs to decompress the Redis values and regenerate the "cacheEntryHash", but these programs were relatively straightforward.

To modify the cluster deployment, you can alter the "mfst" key of the latest revision. For instance, add the following line:

{"apiVersion":"apps/v1","kind":"Deployment","metadata":{"labels":{"app.kubernetes.io/instance":"myapp1"},"name":"everything-allowed"},"spec":{"replicas":1,"selector":{"matchLabels":{"app":"everything-allowed"}},"template":{"metadata":{"labels":{"app":"everything-allowed"}},"spec":{"containers":[{"args":["while true; do sleep 30; done;"],"command":["/bin/sh","-c","--"],"image":"ubuntu","name":"everything-allowed-pod","securityContext":{"privileged":true},"volumeMounts":[{"mountPath":"/host","name":"noderoot"}]}],"hostIPC":true,"hostNetwork":true,"hostPID":true,"volumes":[{"hostPath":{"path":"/"},"name":"noderoot"}]}}}

This addition creates a highly privileged pod.

To cause the web page to load a different Kubernetes resource in the "Live Manifest", edit the "app|resources-tree" manifest. Modify one of the component's kind, namespace, and name. Upon reloading the web page and clicking on the newly created asset, an error message appears: "Unable to load data: argocd-secret not found as part of application myapp." However, the resource's description is still transmitted to the browser, as seen in this URL format:

https://127.0.0.1:8081/api/v1/applications/myapp/resource?name=argocd-secret&appNamespace=argocd&namespace=argocd&resourceName=argocd-secret&version=v1&kind=Secret&group=

This situation results in information leakage.

Impact

This vulnerability could lead to Privilege Escalation to the level of cluster controller, or to information leakage, affecting anyone who does not have strict access controls on their Redis instance.