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Merge pull request #5588 from jorgectf/jorgectf/python/jwt-queries
Python: Add JWT security-related queries
2 parents 8d22db8 + 9ad8a85 commit eed98bd

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‎python/ql/src/experimental/Security/CWE-347/JWTEmptyKeyOrAlgorithm.py‎

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import jwt
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# algorithm set to None
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jwt.encode(payload, "somekey", None)
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# empty key
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jwt.encode(payload, key="", algorithm="HS256")

‎python/ql/src/experimental/Security/CWE-347/JWTEmptyKeyOrAlgorithm.qhelp‎

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<!DOCTYPE qhelp PUBLIC
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"-//Semmle//qhelp//EN"
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"qhelp.dtd">
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<qhelp>
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<overview>
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<p>Applications encoding a JSON Web Token (JWT) may be vulnerable when the applied key or algorithm
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is empty or <code>None</code>.</p>
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</overview>
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<recommendation>
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<p>Use non-empty nor <code>None</code> values while encoding JWT payloads.</p>
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</recommendation>
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<example>
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<p>This example shows two PyJWT encoding calls.
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In the first place, the encoding process use a None algorithm whereas the second example uses an
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empty key. Both examples leave the payload insecurely encoded.
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</p>
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<sample src="JWTEmptyKeyOrAlgorithm.py" />
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</example>
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<references>
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<li>PyJWT: <a href="https://pyjwt.readthedocs.io/en/stable/">Documentation</a>.</li>
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<li>Authlib JWT: <a href="https://docs.authlib.org/en/latest/specs/rfc7519.html">Documentation</a>.</li>
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<li>Python-Jose: <a href="https://github.com/mpdavis/python-jose">Documentation</a>.</li>
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<li>Auth0 Blog: <a href="https://auth0.com/blog/critical-vulnerabilities-in-json-web-token-libraries/#Meet-the--None--Algorithm">Meet the "None" Algorithm</a>.</li>
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</references>
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</qhelp>

‎python/ql/src/experimental/Security/CWE-347/JWTEmptyKeyOrAlgorithm.ql‎

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/**
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* @name JWT encoding using empty key or algorithm
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* @description The application uses an empty secret or algorithm while encoding a JWT Token.
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* @kind problem
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* @problem.severity warning
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* @id py/jwt-empty-secret-or-algorithm
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* @tags security
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*/
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// determine precision above
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import python
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import experimental.semmle.python.Concepts
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import experimental.semmle.python.frameworks.JWT
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from JWTEncoding jwtEncoding, string affectedComponent
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where
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affectedComponent = "algorithm" and
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isEmptyOrNone(jwtEncoding.getAlgorithm())
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or
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affectedComponent = "key" and
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isEmptyOrNone(jwtEncoding.getKey())
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select jwtEncoding, "This JWT encoding has an empty " + affectedComponent + "."

‎python/ql/src/experimental/Security/CWE-347/JWTMissingSecretOrPublicKeyVerification.py‎

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import jwt
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# unverified decoding
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jwt.decode(payload, key="somekey", verify=False)

‎python/ql/src/experimental/Security/CWE-347/JWTMissingSecretOrPublicKeyVerification.qhelp‎

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<!DOCTYPE qhelp PUBLIC
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"-//Semmle//qhelp//EN"
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"qhelp.dtd">
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<qhelp>
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<overview>
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<p>Applications decoding a JSON Web Token (JWT) may be vulnerable when the
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key isn't verified in the process.
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</p>
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</overview>
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<recommendation>
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<p>Set the <code>verify</code> argument to <code>True</code> or use
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a framework that does it by default.
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</p>
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</recommendation>
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<example>
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<p>This example shows a PyJWT encoding call with the <code>verify</code>
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argument set to <code>False</code>.
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</p>
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<sample src="JWTMissingSecretOrPublicKeyVerification.py" />
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</example>
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<references>
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<li>PyJWT: <a href="https://pyjwt.readthedocs.io/en/stable/">Documentation</a>.</li>
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<li>Authlib JWT: <a href="https://docs.authlib.org/en/latest/specs/rfc7519.html">Documentation</a>.</li>
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<li>Python-Jose: <a href="https://github.com/mpdavis/python-jose">Documentation</a>.</li>
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</references>
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</qhelp>

‎python/ql/src/experimental/Security/CWE-347/JWTMissingSecretOrPublicKeyVerification.ql‎

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/**
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* @name JWT missing secret or public key verification
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* @description The application does not verify the JWT payload with a cryptographic secret or public key.
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* @kind problem
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* @problem.severity warning
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* @id py/jwt-missing-verification
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* @tags security
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* external/cwe/cwe-347
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*/
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// determine precision above
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import python
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import experimental.semmle.python.Concepts
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from JWTDecoding jwtDecoding
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where not jwtDecoding.verifiesSignature()
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select jwtDecoding.getPayload(), "is not verified with a cryptographic secret or public key."

‎python/ql/src/experimental/semmle/python/Concepts.qll‎

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*/
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DataFlow::Node getValueArg() { result = range.getValueArg() }
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}
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/** Provides classes for modeling JWT encoding-related APIs. */
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module JWTEncoding {
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/**
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* A data-flow node that collects methods encoding a JWT token.
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*
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* Extend this class to model new APIs. If you want to refine existing API models,
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* extend `JWTEncoding` instead.
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*/
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abstract class Range extends DataFlow::Node {
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/**
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* Gets the argument containing the encoding payload.
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*/
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abstract DataFlow::Node getPayload();
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/**
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* Gets the argument containing the encoding key.
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*/
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abstract DataFlow::Node getKey();
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/**
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* Gets the argument for the algorithm used in the encoding.
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*/
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abstract DataFlow::Node getAlgorithm();
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/**
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* Gets a string representation of the algorithm used in the encoding.
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*/
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abstract string getAlgorithmString();
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}
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}
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/**
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* A data-flow node that collects methods encoding a JWT token.
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*
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* Extend this class to refine existing API models. If you want to model new APIs,
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* extend `JWTEncoding::Range` instead.
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*/
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class JWTEncoding extends DataFlow::Node instanceof JWTEncoding::Range {
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/**
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* Gets the argument containing the payload.
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*/
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DataFlow::Node getPayload() { result = super.getPayload() }
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/**
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* Gets the argument containing the encoding key.
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*/
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DataFlow::Node getKey() { result = super.getKey() }
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/**
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* Gets the argument for the algorithm used in the encoding.
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*/
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DataFlow::Node getAlgorithm() { result = super.getAlgorithm() }
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/**
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* Gets a string representation of the algorithm used in the encoding.
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*/
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string getAlgorithmString() { result = super.getAlgorithmString() }
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}
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/** Provides classes for modeling JWT decoding-related APIs. */
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module JWTDecoding {
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/**
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* A data-flow node that collects methods decoding a JWT token.
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*
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* Extend this class to model new APIs. If you want to refine existing API models,
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* extend `JWTDecoding` instead.
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*/
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abstract class Range extends DataFlow::Node {
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/**
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* Gets the argument containing the encoding payload.
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*/
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abstract DataFlow::Node getPayload();
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/**
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* Gets the argument containing the encoding key.
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*/
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abstract DataFlow::Node getKey();
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/**
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* Gets the argument for the algorithm used in the encoding.
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*/
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abstract DataFlow::Node getAlgorithm();
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/**
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* Gets a string representation of the algorithm used in the encoding.
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*/
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abstract string getAlgorithmString();
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/**
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* Gets the options Node used in the encoding.
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*/
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abstract DataFlow::Node getOptions();
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/**
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* Checks if the signature gets verified while decoding.
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*/
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abstract predicate verifiesSignature();
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}
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}
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/**
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* A data-flow node that collects methods encoding a JWT token.
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*
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* Extend this class to refine existing API models. If you want to model new APIs,
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* extend `JWTDecoding::Range` instead.
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*/
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class JWTDecoding extends DataFlow::Node instanceof JWTDecoding::Range {
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/**
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* Gets the argument containing the payload.
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*/
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DataFlow::Node getPayload() { result = super.getPayload() }
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/**
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* Gets the argument containing the encoding key.
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*/
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DataFlow::Node getKey() { result = super.getKey() }
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/**
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* Gets the argument for the algorithm used in the encoding.
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*/
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DataFlow::Node getAlgorithm() { result = super.getAlgorithm() }
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/**
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* Gets a string representation of the algorithm used in the encoding.
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*/
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string getAlgorithmString() { result = super.getAlgorithmString() }
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/**
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* Gets the options Node used in the encoding.
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*/
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DataFlow::Node getOptions() { result = super.getOptions() }
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/**
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* Checks if the signature gets verified while decoding.
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*/
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predicate verifiesSignature() { super.verifiesSignature() }
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}

‎python/ql/src/experimental/semmle/python/Frameworks.qll‎

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private import experimental.semmle.python.frameworks.LDAP
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private import experimental.semmle.python.frameworks.NoSQL
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private import experimental.semmle.python.frameworks.Log
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private import experimental.semmle.python.frameworks.JWT
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private import experimental.semmle.python.libraries.PyJWT
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private import experimental.semmle.python.libraries.Authlib
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private import experimental.semmle.python.libraries.PythonJose

‎python/ql/src/experimental/semmle/python/frameworks/JWT.qll‎

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private import python
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private import semmle.python.ApiGraphs
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/** Checks if the argument is empty or none. */
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predicate isEmptyOrNone(DataFlow::Node arg) { isEmpty(arg) or isNone(arg) }
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/** Checks if an empty string `""` flows to `arg` */
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predicate isEmpty(DataFlow::Node arg) {
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exists(StrConst emptyString |
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emptyString.getText() = "" and
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DataFlow::exprNode(emptyString).(DataFlow::LocalSourceNode).flowsTo(arg)
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)
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}
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/** Checks if `None` flows to `arg` */
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predicate isNone(DataFlow::Node arg) {
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DataFlow::exprNode(any(None no)).(DataFlow::LocalSourceNode).flowsTo(arg)
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}
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/** Checks if `False` flows to `arg` */
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predicate isFalse(DataFlow::Node arg) {
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DataFlow::exprNode(any(False falseExpr)).(DataFlow::LocalSourceNode).flowsTo(arg)
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}

‎python/ql/src/experimental/semmle/python/libraries/Authlib.qll‎

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private import python
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private import experimental.semmle.python.Concepts
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private import semmle.python.ApiGraphs
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private import experimental.semmle.python.frameworks.JWT
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private module Authlib {
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/** Gets a reference to `authlib.jose.(jwt|JsonWebToken)` */
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private API::Node authlibJWT() {
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result in [
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API::moduleImport("authlib").getMember("jose").getMember("jwt"),
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API::moduleImport("authlib").getMember("jose").getMember("JsonWebToken").getReturn()
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]
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}
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/** Gets a reference to `jwt.encode` */
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private API::Node authlibJWTEncode() { result = authlibJWT().getMember("encode") }
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/** Gets a reference to `jwt.decode` */
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private API::Node authlibJWTDecode() { result = authlibJWT().getMember("decode") }
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/**
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* Gets a call to `authlib.jose.(jwt|JsonWebToken).encode`.
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*
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* Given the following example:
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*
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* ```py
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* jwt.encode({"alg": "HS256"}, token, "key")
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* ```
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*
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* * `this` would be `jwt.encode({"alg": "HS256"}, token, "key")`.
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* * `getPayload()`'s result would be `token`.
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* * `getKey()`'s result would be `"key"`.
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* * `getAlgorithm()`'s result would be `"HS256"`.
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* * `getAlgorithmstring()`'s result would be `HS256`.
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*/
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private class AuthlibJWTEncodeCall extends DataFlow::CallCfgNode, JWTEncoding::Range {
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AuthlibJWTEncodeCall() { this = authlibJWTEncode().getACall() }
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override DataFlow::Node getPayload() { result = this.getArg(1) }
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override DataFlow::Node getKey() { result = this.getArg(2) }
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override DataFlow::Node getAlgorithm() {
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exists(KeyValuePair headerDict |
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headerDict = this.getArg(0).asExpr().(Dict).getItem(_) and
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headerDict.getKey().(Str_).getS().matches("alg") and
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result.asExpr() = headerDict.getValue()
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)
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}
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override string getAlgorithmString() {
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exists(StrConst str |
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DataFlow::exprNode(str).(DataFlow::LocalSourceNode).flowsTo(getAlgorithm()) and
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result = str.getText()
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)
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}
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}
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/**
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* Gets a call to `authlib.jose.(jwt|JsonWebToken).decode`
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*
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* Given the following example:
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*
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* ```py
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* jwt.decode(token, key)
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* ```
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*
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* * `this` would be `jwt.decode(token, key)`.
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* * `getPayload()`'s result would be `token`.
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* * `getKey()`'s result would be `key`.
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*/
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private class AuthlibJWTDecodeCall extends DataFlow::CallCfgNode, JWTDecoding::Range {
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AuthlibJWTDecodeCall() { this = authlibJWTDecode().getACall() }
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override DataFlow::Node getPayload() { result = this.getArg(0) }
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override DataFlow::Node getKey() { result = this.getArg(1) }
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override DataFlow::Node getAlgorithm() { none() }
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override string getAlgorithmString() { none() }
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override DataFlow::Node getOptions() { none() }
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override predicate verifiesSignature() { any() }
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}
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}

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