False positive: Full server-side request forgery

[markdboyd]

Description of the false positive

I have seen alerts for "Full server-side request forgery" (id: py/full-ssrf), even though the code has a valid mitigation in place. CodeQL also isn't recognizing other valid mitigations for this vulnerability.

For example, given this code:

   url = request.url.replace(request.host_url, "my-expected-host-url")

    resp = requests.request(
        url=url,
    )

As you can see, this code is already using request.url.replace to control the requested URL and ensure that malicious requests cannot manipulate the destination of the request. However, CodeQL does not recognize this method as a valid mitigation for SSRF.

I also tried:

   from urllib.parse import urljoin

   url = urljoin("my-expected-host-url", request.path)

CodeQL does not accept this approach either.

The only approach that CodeQL accepts is string concatenation:

   url = "my-expected-host-url" + request.path

Having to use string concatenation instead of urljoin is not ideal.

[rvermeulen]

Hi @markdboyd,

Thanks for reporting this. We indeed only seem to support the string concatenation sanitizer https://github.com/github/codeql/blob/ad5c5acae500e8d1742c3c5ff7ecaece2fe3ddcb/python/ql/lib/semmle/python/security/dataflow/ServerSideRequestForgeryCustomizations.qll#L94C61-L94C84

I will pass this information to the team implementing the Python queries.