CVE-2026-27598: Dagu: Path traversal in DAG creation allows arbitrary YAML file write outside DAGs directory

The CreateNewDAG API endpoint (POST /api/v1/dags) does not validate the DAG name before passing it to the file store. While RenameDAG calls core.ValidateDAGName() to reject names containing path separators (line 273 in dags.go), CreateNewDAG skips this validation entirely and passes user input directly to dagStore.Create().

In internal/persis/filedag/store.go, the generateFilePath function (line 493) checks if the name contains a path separator, and if so, resolves it via filepath.Abs(name) — completely ignoring the baseDir. This means a name like ../../tmp/pwned will write a file to /tmp/pwned.yaml instead of the DAGs directory.

Affected code:

internal/service/frontend/api/v1/dags.go line 120-170 — CreateNewDAG handler, no call to ValidateDAGName

internal/persis/filedag/store.go line 493-498 — generateFilePath resolves absolute path when name contains separator

internal/persis/filedag/store.go line 213 — Create calls generateFilePath and writes attacker-controlled YAML content to the resolved path

PoC:

curl -X POST http://localhost:8080/api/v1/dags \
-H "Content-Type: application/json" \
-d '{
"name": "../../tmp/path-traversal-proof",
"spec": "steps:\n  - command: id > /tmp/pwned\n"
}'

After this request, a file /tmp/path-traversal-proof.yaml will be created with the attacker-supplied content. The file will be written with the permissions of the dagu process.

An authenticated user with DAG write permissions can write arbitrary YAML files anywhere on the filesystem (limited by the process permissions). Since dagu executes DAG files as shell commands, writing a malicious DAG to the DAGs directory of another instance or overwriting config files can lead to remote code execution.