CVE-2026-42183: Github.com/argoproj/argo workflows/v4 Denial of Service Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-p4gq-3vxj-f4jq",
  "modified" : "2026-05-13T13:39:11Z",
  "published" : "2026-05-04T20:01:13Z",
  "aliases" : [ "CVE-2026-42183" ],
  "summary" : "Argo Affected by SSO RBAC Delegation Nil Pointer Dereference DoS (gatekeeper.go)",
  "details" : "### Summary\nA 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`.\n\n### Details\nWhen `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.\n\n**Affected code (v4.0.4):**\n\n```go\n// gatekeeper.go:304\n} else if precedence(namespaceAccount) > precedence(loginAccount) {\n    // loginAccount is nil here -> precedence(nil) -> PANIC\n\n// gatekeeper.go:232-234\nfunc precedence(serviceAccount *corev1.ServiceAccount) int {\n    i, _ := strconv.Atoi(serviceAccount.Annotations[common.AnnotationKeyRBACRulePrecedence])\n    return i\n}\n```\n\n### PoC\n**Live-tested 2026-04-17:** kind cluster, Argo Workflows v4.0.4, Dex v2.43.1 OIDC provider.\n\n1. Deploy Argo Workflows with `--auth-mode=sso --auth-mode=client`, SSO pointing to Dex, RBAC enabled.\n2. Set `SSO_DELEGATE_RBAC_TO_NAMESPACE=true` on the argo-server deployment.\n3. Create an RBAC ServiceAccount with `workflows.argoproj.io/rbac-rule: \"true\"` annotation in a target namespace (e.g., `target-ns`).\n4. Do **not** create a matching RBAC rule in the SSO namespace (`argo`).\n5. Authenticate via the Dex SSO flow.\n6. Request `GET /api/v1/workflows/target-ns` with the SSO session cookie.\n7. Server returns HTTP 500: `{\"code\":13,\"message\":\"runtime error: invalid memory address or nil pointer dereference\"}`\n8. Server logs: `Recovered from panic` with stack trace at `gatekeeper.go:233` (`precedence()`) called from `gatekeeper.go:304`.\n\nEvery subsequent API request from affected SSO users triggers the same panic.\n\n### Impact\nPermanent 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.\n\n### Suggested Fix\nAdd nil check: `if loginAccount == nil || precedence(namespaceAccount) > precedence(loginAccount)`\n\n### AI Disclosure\nThis advisory was prepared with AI assistance (Claude Code, Anthropic).",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/argoproj/argo-workflows/v4"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.0.0"
      }, {
        "fixed" : "4.0.5"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.0.4"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/argoproj/argo-workflows/security/advisories/GHSA-p4gq-3vxj-f4jq"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-42183"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/argoproj/argo-workflows/commit/c4cc17d0c034fa9a9cc01ef1af6c8016c93071d4"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/argoproj/argo-workflows"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/argoproj/argo-workflows/releases/tag/v4.0.5"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-476" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-04T20:01:13Z",
    "nvd_published_at" : "2026-05-09T04:16:23Z"
  }
}