CVE-2026-42183

A nil pointer dereference in server/auth/gatekeeper.go rbacAuthorization() causes a panic (denial of service) for SSO users whose claims match a namespace-level RBAC rule but not an SSO-namespace rule, when SSO_DELEGATE_RBAC_TO_NAMESPACE=true.

Details

When getServiceAccount(claims, ssoNamespace) returns nil (no matching rule), the error is suppressed and loginAccount remains nil. If RBAC delegation finds a matching namespaceAccount, line 304 calls precedence(loginAccount) which unconditionally accesses serviceAccount.Annotations, nil pointer dereference.

Affected code (v4.0.4):

// gatekeeper.go:304
} else if precedence(namespaceAccount) > precedence(loginAccount) {
    // loginAccount is nil here -> precedence(nil) -> PANIC

// gatekeeper.go:232-234
func precedence(serviceAccount *corev1.ServiceAccount) int {
    i, _ := strconv.Atoi(serviceAccount.Annotations[common.AnnotationKeyRBACRulePrecedence])
    return i
}

PoC

Live-tested 2026-04-17: kind cluster, Argo Workflows v4.0.4, Dex v2.43.1 OIDC provider.

1. Deploy Argo Workflows with --auth-mode=sso --auth-mode=client, SSO pointing to Dex, RBAC enabled.
2. Set SSO_DELEGATE_RBAC_TO_NAMESPACE=true on the argo-server deployment.
3. Create an RBAC ServiceAccount with workflows.argoproj.io/rbac-rule: "true" annotation in a target namespace (e.g., target-ns).
4. Do not create a matching RBAC rule in the SSO namespace (argo).
5. Authenticate via the Dex SSO flow.
6. Request GET /api/v1/workflows/target-ns with the SSO session cookie.
7. Server returns HTTP 500: {"code":13,"message":"runtime error: invalid memory address or nil pointer dereference"}
8. Server logs: Recovered from panic with stack trace at gatekeeper.go:233 (precedence()) called from gatekeeper.go:304.

Every subsequent API request from affected SSO users triggers the same panic.

AI Disclosure

This advisory was prepared with AI assistance (Claude Code, Anthropic).

Permanent denial of service for any SSO user whose claims don't match SSO-namespace RBAC but do match a target namespace rule. Realistic in multi-tenant deployments with per-namespace RBAC. The gRPC recovery interceptor catches the panic so the server process survives, but the affected user gets HTTP 500 on every request.

The application dereferences a null pointer, causing a crash. Typical impact: denial of service via crash.

Kodem intelligence

Add nil check: if loginAccount == nil || precedence(namespaceAccount) > precedence(loginAccount)

1. What is CVE-2026-42183? CVE-2026-42183 is a low-severity null pointer dereference vulnerability in github.com/argoproj/argo-workflows/v4 (go), affecting versions >= 4.0.0, <= 4.0.4. It is fixed in 4.0.5. The application dereferences a null pointer, causing a crash.
2. Which versions of github.com/argoproj/argo-workflows/v4 are affected by CVE-2026-42183? github.com/argoproj/argo-workflows/v4 (go) versions >= 4.0.0, <= 4.0.4 is affected.
3. Is there a fix for CVE-2026-42183? Yes. CVE-2026-42183 is fixed in 4.0.5. Upgrade to this version or later.
4. Is CVE-2026-42183 exploitable, and should I be worried? Whether CVE-2026-42183 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
5. What actually determines whether CVE-2026-42183 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
6. How do I fix CVE-2026-42183? Upgrade github.com/argoproj/argo-workflows/v4 to 4.0.5 or later.