ID: py/client-exposed-cookie Kind: problem Security severity: 5.0 Severity: warning Precision: high Tags: - security - external/cwe/cwe-1004 Query suites: - python-code-scanning.qls - python-security-extended.qls - python-security-and-quality.qls
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Cookies without the HttpOnly flag set are accessible to JavaScript running in the same origin. In case of a Cross-Site Scripting (XSS) vulnerability, the cookie can be stolen by a malicious script. If a sensitive cookie does not need to be accessed directly by client-side JS, the HttpOnly flag should be set.
Recommendation¶
Set httponly to True, or add ; HttpOnly; to the cookie’s raw header value, to ensure that the cookie is not accessible via JavaScript.
Example¶
In the following examples, the cases marked GOOD show secure cookie attributes being set; whereas in the case marked BAD they are not set.
from flask import Flask, request, make_response, Response @app.route("/good1") def good1(): resp = make_response() resp.set_cookie("sessionid", value="value", secure=True, httponly=True, samesite='Strict') # GOOD: Attributes are securely set return resp @app.route("/good2") def good2(): resp = make_response() resp.headers['Set-Cookie'] = "sessionid=value; Secure; HttpOnly; SameSite=Strict" # GOOD: Attributes are securely set return resp @app.route("/bad1") def bad1(): resp = make_response() resp.set_cookie("sessionid", value="value", samesite='None') # BAD: the SameSite attribute is set to 'None' and the 'Secure' and 'HttpOnly' attributes are set to False by default. return resp
References¶
PortSwigger: Cookie without HttpOnly flag set
MDN: Set-Cookie.
Common Weakness Enumeration: CWE-1004.