Dalfox, an XSS scanner, allows unauthenticated attackers to read arbitrary files on the host via the custom‑payload‑file parameter when running in REST API server mode. The parameter is deserialized directly from the request body and passed to voltFile.ReadLinesOrLiteral, which reads any file accessible to the Dalfox process. Each line of the file is embedded as an XSS payload in outbound HTTP requests to an attacker‑controlled target, enabling out‑of‑band exfiltration of the file contents.

All installations of the hahwul Dalfox utility prior to version 2.13.0 that are configured to run in server mode without an API key are vulnerable. The problem exists in the custom‑payload‑file field of the model.Options structure, which is exposed via the REST API.

The CVSS score of 7.5 indicates a high severity vulnerability. Because the attack requires only unauthenticated network access to the API endpoint and no special privileges, the EPSS score is not available but the risk remains significant. The vulnerability is not listed in CISA's KEV catalog, yet it allows direct read of any file that the Dalfox process can access, making it a serious confidentiality threat. The likely attack path is through an HTTP POST or similar request supplying a malicious custom‑payload‑file value while the server is running without an API key.