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Merge pull request #6989 from RasmusWL/flask-file-sending-fixup
Python: Small fixup for `flask.send_from_directory`
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‎python/change-notes/2021-10-28-flask-send_file.md

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lgtm,codescanning
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* Added modeling of the `send_from_directory` and `send_file` functions from the `flask` PyPI package, resulting in additional sinks for the _Uncontrolled data used in path expression_ (`py/path-injection`) query. This addition was originally [submitted as an external contribution by @porcupineyhairs](https://github.com/github/codeql/pull/6330).

‎python/ql/lib/semmle/python/frameworks/Flask.qll

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@@ -11,6 +11,7 @@ private import semmle.python.Concepts
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private import semmle.python.frameworks.Werkzeug
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private import semmle.python.ApiGraphs
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private import semmle.python.frameworks.internal.InstanceTaintStepsHelper
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private import semmle.python.security.dataflow.PathInjectionCustomizations
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/**
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* Provides models for the `flask` PyPI package.
@@ -525,13 +526,30 @@ module Flask {
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*
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* See https://flask.palletsprojects.com/en/1.1.x/api/#flask.send_from_directory
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*/
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class FlaskSendFromDirectory extends FileSystemAccess::Range, DataFlow::CallCfgNode {
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FlaskSendFromDirectory() {
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private class FlaskSendFromDirectoryCall extends FileSystemAccess::Range, DataFlow::CallCfgNode {
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FlaskSendFromDirectoryCall() {
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this = API::moduleImport("flask").getMember("send_from_directory").getACall()
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}
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override DataFlow::Node getAPathArgument() {
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result in [this.getArg(_), this.getArgByName(["directory", "filename"])]
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result in [
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this.getArg(0), this.getArgByName("directory"),
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// as described in the docs, the `filename` argument is restrained to be within
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// the provided directory, so is not exposed to path-injection. (but is still a
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// path-argument).
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this.getArg(1), this.getArgByName("filename")
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]
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}
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}
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/**
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* To exclude `filename` argument to `flask.send_from_directory` as a path-injection sink.
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*/
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private class FlaskSendFromDirectoryCallFilenameSanitizer extends PathInjection::Sanitizer {
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FlaskSendFromDirectoryCallFilenameSanitizer() {
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this = any(FlaskSendFromDirectoryCall c).getArg(1)
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or
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this = any(FlaskSendFromDirectoryCall c).getArgByName("filename")
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}
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}
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*
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* See https://flask.palletsprojects.com/en/1.1.x/api/#flask.send_file
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*/
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class FlaskSendFile extends FileSystemAccess::Range, DataFlow::CallCfgNode {
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FlaskSendFile() { this = API::moduleImport("flask").getMember("send_file").getACall() }
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private class FlaskSendFileCall extends FileSystemAccess::Range, DataFlow::CallCfgNode {
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FlaskSendFileCall() { this = API::moduleImport("flask").getMember("send_file").getACall() }
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override DataFlow::Node getAPathArgument() {
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result in [this.getArg(0), this.getArgByName("filename_or_fp")]

‎python/ql/lib/semmle/python/security/dataflow/PathInjection.qll

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@@ -26,7 +26,11 @@ class PathNotNormalizedConfiguration extends TaintTracking::Configuration {
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override predicate isSink(DataFlow::Node sink) { sink instanceof Sink }
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override predicate isSanitizer(DataFlow::Node node) { node instanceof Path::PathNormalization }
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override predicate isSanitizer(DataFlow::Node node) {
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node instanceof Sanitizer
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or
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node instanceof Path::PathNormalization
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}
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override predicate isSanitizerGuard(DataFlow::BarrierGuard guard) {
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guard instanceof SanitizerGuard
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override predicate isSink(DataFlow::Node sink) { sink instanceof Path::PathNormalization }
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override predicate isSanitizer(DataFlow::Node node) { node instanceof Sanitizer }
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override predicate isSanitizerOut(DataFlow::Node node) { node instanceof Path::PathNormalization }
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override predicate isSanitizerGuard(DataFlow::BarrierGuard guard) {
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override predicate isSink(DataFlow::Node sink) { sink instanceof Sink }
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override predicate isSanitizer(DataFlow::Node node) { node instanceof Sanitizer }
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override predicate isSanitizerGuard(DataFlow::BarrierGuard guard) {
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guard instanceof Path::SafeAccessCheck
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or

‎python/ql/lib/semmle/python/security/dataflow/PathInjectionCustomizations.qll

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@@ -32,6 +32,16 @@ module PathInjection {
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*/
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abstract class Sink extends DataFlow::Node { }
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/**
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* A sanitizer for "path injection" vulnerabilities.
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*
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* This should only be used for things like calls to library functions that perform their own
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* (correct) normalization/escaping of untrusted paths.
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*
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* Please also see `Path::SafeAccessCheck` and `Path::PathNormalization` Concepts.
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*/
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abstract class Sanitizer extends DataFlow::Node { }
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/**
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* A sanitizer guard for "path injection" vulnerabilities.
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*/

‎python/ql/test/library-tests/frameworks/flask/file_sending.py

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from flask import send_from_directory, send_file
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send_from_directory("dir", "file") # $ getAPathArgument="dir" getAPathArgument="file"
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send_from_directory(directory="dir", filename="file") # $ getAPathArgument="dir" getAPathArgument="file"
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send_file("file") # $ getAPathArgument="file"
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send_file(filename_or_fp="file") # $ getAPathArgument="file"

‎python/ql/test/library-tests/frameworks/flask/save_uploaded_file.py

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@@ -1,17 +1,6 @@
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from flask import Flask, request, send_from_directory, send_file
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from flask import Flask, request
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app = Flask(__name__)
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@app.route("/save-uploaded-file") # $routeSetup="/save-uploaded-file"
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def test_taint(): # $requestHandler
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request.files['key'].save("path") # $ getAPathArgument="path"
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@app.route("/path-injection") # $routeSetup="/path-injection"
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def test_path(): # $requestHandler
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send_from_directory("filepath","file") # $ getAPathArgument="filepath" getAPathArgument="file"
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send_file("file") # $ getAPathArgument="file"
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send_from_directory(directory="filepath","file") # $ getAPathArgument="filepath" getAPathArgument="file"
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send_from_directory(filename="filepath","file") # $ getAPathArgument="filepath" getAPathArgument="file"
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send_file(filename_or_fp="file") # $ getAPathArgument="file"

‎python/ql/test/query-tests/Security/CWE-022-PathInjection/PathInjection.expected

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edges
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| flask_path_injection.py:19:15:19:21 | ControlFlowNode for request | flask_path_injection.py:19:15:19:26 | ControlFlowNode for Attribute |
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| flask_path_injection.py:19:15:19:26 | ControlFlowNode for Attribute | flask_path_injection.py:21:32:21:38 | ControlFlowNode for dirname |
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| path_injection.py:12:16:12:22 | ControlFlowNode for request | path_injection.py:12:16:12:27 | ControlFlowNode for Attribute |
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| path_injection.py:12:16:12:27 | ControlFlowNode for Attribute | path_injection.py:13:14:13:47 | ControlFlowNode for Attribute() |
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| path_injection.py:19:16:19:22 | ControlFlowNode for request | path_injection.py:19:16:19:27 | ControlFlowNode for Attribute |
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| test_chaining.py:41:9:41:16 | ControlFlowNode for source() | test_chaining.py:42:9:42:19 | ControlFlowNode for normpath() |
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| test_chaining.py:44:13:44:23 | ControlFlowNode for normpath() | test_chaining.py:45:14:45:14 | ControlFlowNode for z |
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nodes
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| flask_path_injection.py:19:15:19:21 | ControlFlowNode for request | semmle.label | ControlFlowNode for request |
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| flask_path_injection.py:19:15:19:26 | ControlFlowNode for Attribute | semmle.label | ControlFlowNode for Attribute |
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| flask_path_injection.py:21:32:21:38 | ControlFlowNode for dirname | semmle.label | ControlFlowNode for dirname |
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| path_injection.py:12:16:12:22 | ControlFlowNode for request | semmle.label | ControlFlowNode for request |
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| path_injection.py:12:16:12:27 | ControlFlowNode for Attribute | semmle.label | ControlFlowNode for Attribute |
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| path_injection.py:13:14:13:47 | ControlFlowNode for Attribute() | semmle.label | ControlFlowNode for Attribute() |
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| test_chaining.py:44:13:44:23 | ControlFlowNode for normpath() | semmle.label | ControlFlowNode for normpath() |
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| test_chaining.py:45:14:45:14 | ControlFlowNode for z | semmle.label | ControlFlowNode for z |
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#select
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| flask_path_injection.py:21:32:21:38 | ControlFlowNode for dirname | flask_path_injection.py:19:15:19:21 | ControlFlowNode for request | flask_path_injection.py:21:32:21:38 | ControlFlowNode for dirname | This path depends on $@. | flask_path_injection.py:19:15:19:21 | ControlFlowNode for request | a user-provided value |
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| path_injection.py:13:14:13:47 | ControlFlowNode for Attribute() | path_injection.py:12:16:12:22 | ControlFlowNode for request | path_injection.py:13:14:13:47 | ControlFlowNode for Attribute() | This path depends on $@. | path_injection.py:12:16:12:22 | ControlFlowNode for request | a user-provided value |
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| path_injection.py:21:14:21:18 | ControlFlowNode for npath | path_injection.py:19:16:19:22 | ControlFlowNode for request | path_injection.py:21:14:21:18 | ControlFlowNode for npath | This path depends on $@. | path_injection.py:19:16:19:22 | ControlFlowNode for request | a user-provided value |
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| path_injection.py:31:14:31:18 | ControlFlowNode for npath | path_injection.py:27:16:27:22 | ControlFlowNode for request | path_injection.py:31:14:31:18 | ControlFlowNode for npath | This path depends on $@. | path_injection.py:27:16:27:22 | ControlFlowNode for request | a user-provided value |

‎python/ql/test/query-tests/Security/CWE-022-PathInjection/flask_path_injection.py

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from flask import Flask, request, send_from_directory
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app = Flask(__name__)
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STATIC_DIR = "/server/static/"
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# see https://flask.palletsprojects.com/en/1.1.x/api/#flask.send_from_directory
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@app.route("/provide-filename")
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def download_file():
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filename = request.args.get('filename', '')
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# ok since `send_from_directory` ensure this stays within `STATIC_DIR`
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return send_from_directory(STATIC_DIR, filename) # OK
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# see https://flask.palletsprojects.com/en/1.1.x/api/#flask.send_from_directory
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@app.route("/also-provide-dirname")
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def download_file():
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dirname = request.args.get('dirname', '')
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filename = request.args.get('filename', '')
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return send_from_directory(dirname, filename) # NOT OK

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