AntiSSRFPolicy.get_antissrf_session Method

Definition

This method retrieves an AntiSSRFSession, which extends requests.Session and applies the existing AntiSSRFPolicy instance to all requests before sending them. If a request does not meet the requirements of the policy, attempting to make the request will raise an AntiSSRFError.

def get_antissrf_session(options: any) -> AntiSSRFSession

Constraints

There are a couple of methods of the session that are used to apply the policy and therefore should not be overwritten. This includes the mount method for mounting an HTTPAdapter and the build_connection_pool_key_attributes method within our custom AntiSSRFHTTPAdapter where the SSRF protections are implemented.

Parameters

options: any

Any options for a requests.Session

Examples

# Customize the external policy to require the example-required-header header
policy = AntiSSRFPolicy(PolicyConfigOptions.EXTERNAL_ONLY_LATEST)
policy.add_required_headers(["example-required-header"])
session = policy.get_antissrf_session()

# Requests that do not follow the policy will be rejected
try:
    bad_response = session.get(
        "https://learn.microsoft.com/en-us/training/paths/describe-basic-concepts-of-cybersecurity/"
    )
    # Will not get here, since the request does not have the required header
except AntiSSRFError as err:
    # Will get here with the error: AntiSSRFError("Request headers or protocol disallowed by policy")
    pass

# Requests that follow the policy will be made like usual
try:
    good_response = session.get(
        "https://learn.microsoft.com/en-us/training/paths/describe-basic-concepts-of-cybersecurity/",
        headers={"example-required-header": "true"}
    )
    # Will get here, since the request has the required header
except AntiSSRFError as err:
    # Will not get here
    pass

Security Notes

TOCTOU Vulnerabilities

AntiSSRFPolicy only protects requests when it is applied through an AntiSSRFSession at the time the request is made.

One common mistake is validating a URL with AntiSSRF before making a request, then using a separate network component to send that request. With this pattern, your request is not protected by AntiSSRF, and you are exposed to TOCTOU-based SSRF vulnerabilities.

Proxy Support

Proxies are not supported by AntiSSRF. If you configure a proxy on your underlying system or for a particular request, no error or warning will be raised. However, the behavior will likely not match your expectations:

• Only the proxy address itself is validated against the policy’s security requirements.
• AntiSSRF has no control over proxy behavior and cannot be used to block the final destination address.
• Unless the proxy itself is independently configured to use AntiSSRF (or another SSRF protection), SSRF vulnerabilities can occur through the proxy.

For these reasons, do not use proxies with AntiSSRF-protected clients.

Do not configure proxies via any of the following:

• session.proxies dictionary
• Custom HTTPAdapter with proxy support
• Any proxy-aware mount configurations
• OS environment variables (HTTP_PROXY, HTTPS_PROXY)

Note that the requests library automatically respects proxy environment variables. Ensure your application does not implicitly use system proxy settings when creating sessions for AntiSSRF.