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Python: Add json.dumps() as XSS sanitizer #19

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Python: Add json.dumps() as XSS sanitizer #19

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12 changes: 12 additions & 0 deletions python/ql/lib/semmle/python/security/dataflow/ReflectedXSSCustomizations.qll
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@ private import semmle.python.Concepts
private import semmle.python.frameworks.data.ModelsAsData
private import semmle.python.dataflow.new.RemoteFlowSources
private import semmle.python.dataflow.new.BarrierGuards
private import semmle.python.ApiGraphs

/**
* Provides default sources, sinks and sanitizers for detecting
Expand Down Expand Up @@ -91,4 +92,15 @@ module ReflectedXss {
class SanitizerFromModel extends Sanitizer {
SanitizerFromModel() { ModelOutput::barrierNode(this, ["html-injection", "js-injection"]) }
}

/**
* A call to `json.dumps()`, considered as a sanitizer.
* The output of json.dumps is JSON-formatted data typically returned
* with application/json Content-Type, which browsers do not render as HTML.
*/
class JsonDumpsSanitizer extends Sanitizer {
JsonDumpsSanitizer() {
this = API::moduleImport("json").getMember("dumps").getACall()
}
}
}
19 changes: 19 additions & 0 deletions python/ql/test/query-tests/Security/CWE-079-ReflectedXss/json_response.py
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@@ -0,0 +1,19 @@
import json
from flask import Flask, request, make_response

app = Flask(__name__)


@app.route("/api/data")
def json_api_response():
"""json.dumps output is safe - JSON-encoded data is not rendered as HTML."""
user_input = request.args.get("data", "")
result = json.dumps({"input": user_input})
return make_response(result, 200, {"Content-Type": "application/json"}) # Safe


@app.route("/unsafe")
def unsafe_html_response():
"""Without json.dumps, user input in HTML response is unsafe."""
user_input = request.args.get("data", "")
return make_response("<html>" + user_input + "</html>") # $ Alert
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