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Max Schaefer
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JavaScript: Add query IncompleteUrlSchemeCheck.ql.
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‎change-notes/1.23/analysis-javascript.md‎

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| Useless regular expression character escape (`js/useless-regexp-character-escape`) | correctness, security, external/cwe/cwe-20 | Highlights regular expression strings with useless character escapes, indicating a possible violation of [CWE-20](https://cwe.mitre.org/data/definitions/20.html). Results are shown on LGTM by default. |
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| Unreachable method overloads (`js/unreachable-method-overloads`) | correctness, typescript | Highlights method overloads that are impossible to use from client code. Results are shown on LGTM by default. |
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| Ignoring result from pure array method (`js/ignore-array-result`) | maintainability, correctness | Highlights calls to array methods without side effects where the return value is ignored. Results are shown on LGTM by default. |
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| Incomplete URL scheme check (`js/incomplete-url-scheme-check`) | security, correctness, external/cwe/cwe-020 | Highlights checks for `javascript:` URLs that do not take `data:` or `vbscript:` URLs into account. |
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## Changes to existing queries
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‎javascript/config/suites/javascript/security‎

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+ semmlecode-javascript-queries/DOM/TargetBlank.ql: /Security/CWE/CWE-200
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+ semmlecode-javascript-queries/Electron/EnablingNodeIntegration.ql: /Security/CWE/CWE-094
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+ semmlecode-javascript-queries/Security/CWE-020/IncompleteHostnameRegExp.ql: /Security/CWE/CWE-020
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+ semmlecode-javascript-queries/Security/CWE-020/IncompleteUrlSchemeCheck.ql: /Security/CWE/CWE-020
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+ semmlecode-javascript-queries/Security/CWE-020/IncompleteUrlSubstringSanitization.ql: /Security/CWE/CWE-020
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+ semmlecode-javascript-queries/Security/CWE-020/IncorrectSuffixCheck.ql: /Security/CWE/CWE-020
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+ semmlecode-javascript-queries/Security/CWE-020/MissingRegExpAnchor.ql: /Security/CWE/CWE-020

‎javascript/ql/src/Security/CWE-020/IncompleteUrlSchemeCheck.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>
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URLs starting with <code>javascript:</code> can be used to encode JavaScript code to be executed
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when the URL is visited. While this is a powerful mechanism for creating feature-rich and responsive
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web applications, it is also a potential security risk: if the URL comes from an untrusted source,
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it might contain harmful JavaScript code. For this reason, many frameworks and libraries first check
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the URL scheme of any untrusted URL, and reject URLs with the <code>javascript:</code> scheme.
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</p>
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<p>
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However, the <code>data:</code> and <code>vbscript:</code> schemes can be used to represent
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executable code in a very similar way, so any validation logic that checks against
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<code>javascript:</code> but not against <code>data:</code> and <code>vbscript:</code> is likely to
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be insufficient.
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</p>
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</overview>
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<recommendation>
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<p>
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Add checks covering both <code>data:</code> and <code>vbscript:</code>.
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</p>
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</recommendation>
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<example>
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<p>
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The following function validates a (presumably untrusted) URL <code>url</code>. If it starts with
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<code>javascript:</code> (case-insensitive and potentially preceded by whitespace), the harmless
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placeholder URL <code>about:blank</code> is returned to prevent code injection; otherwise
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<code>url</code> itself is returned.
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</p>
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<sample src="examples/IncompleteUrlSchemeCheck.js"/>
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<p>
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While this check provides partial projection, it should be extended to cover <code>data:</code>
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and <code>vbscript:</code> as well:
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</p>
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<sample src="examples/IncompleteUrlSchemeCheckGood.js"/>
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</example>
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<references>
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<li>WHATWG: <a href="https://wiki.whatwg.org/wiki/URL_schemes">URL schemes</a>.</li>
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</references>
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</qhelp>

‎javascript/ql/src/Security/CWE-020/IncompleteUrlSchemeCheck.ql‎

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/**
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* @name Incomplete URL scheme check
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* @description Checking for the "javascript:" URL scheme without also checking for "vbscript:"
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* and "data:" suggests a logic error or even a security vulnerability.
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* @kind problem
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* @problem.severity warning
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* @precision high
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* @id js/incomplete-url-scheme-check
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* @tags security
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* correctness
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* external/cwe/cwe-020
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*/
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import javascript
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import semmle.javascript.dataflow.internal.AccessPaths
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/** A URL scheme that can be used to represent executable code. */
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class DangerousScheme extends string {
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DangerousScheme() { this = "data:" or this = "javascript:" or this = "vbscript:" }
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}
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/** Gets a data-flow node that checks `nd` against the given `scheme`. */
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DataFlow::Node schemeCheck(
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DataFlow::Node nd, DangerousScheme scheme
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) {
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// check of the form `nd.startsWith(scheme)`
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exists(StringOps::StartsWith sw | sw = result |
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sw.getBaseString() = nd and
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sw.getSubstring().mayHaveStringValue(scheme)
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)
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or
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// propagate through trimming, case conversion, and regexp replace
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exists(DataFlow::MethodCallNode stringop |
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stringop.getMethodName().matches("trim%") or
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stringop.getMethodName().matches("to%Case") or
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stringop.getMethodName() = "replace"
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|
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result = schemeCheck(stringop, scheme) and
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nd = stringop.getReceiver()
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)
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or
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// propagate througb local data flow
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result = schemeCheck(nd.getASuccessor(), scheme)
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}
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/** Gets a data-flow node that checks an instance of `ap` against the given `scheme`. */
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DataFlow::Node schemeCheckOn(AccessPath ap, DangerousScheme scheme) {
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result = schemeCheck(ap.getAnInstance().flow(), scheme)
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}
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from AccessPath ap, int n
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where
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n = strictcount(DangerousScheme s) and
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strictcount(DangerousScheme s | exists(schemeCheckOn(ap, s))) < n
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select schemeCheckOn(ap, "javascript:"),
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"This check does not consider " +
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strictconcat(DangerousScheme s | not exists(schemeCheckOn(ap, s)) | s, " and ") + "."

‎javascript/ql/src/Security/CWE-020/examples/IncompleteUrlSchemeCheck.js‎

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function sanitizeUrl(url) {
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let u = decodeURI(url).trim().toLowerCase();
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if (u.startsWith("javascript:"))
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return "about:blank";
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return url;
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}

‎javascript/ql/src/Security/CWE-020/examples/IncompleteUrlSchemeCheckGood.js‎

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function sanitizeUrl(url) {
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let u = decodeURI(url).trim().toLowerCase();
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if (u.startsWith("javascript:") || u.startsWith("data:") || u.startsWith("vbscript:"))
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return "about:blank";
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return url;
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}

‎javascript/ql/test/query-tests/Security/CWE-020/IncompleteUrlSchemeCheck.expected‎

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| IncompleteUrlSchemeCheck.js:3:9:3:35 | u.start ... ript:") | This check does not consider data: and vbscript:. |

‎javascript/ql/test/query-tests/Security/CWE-020/IncompleteUrlSchemeCheck.js‎

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function sanitizeUrl(url) {
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let u = decodeURI(url).trim().toLowerCase();
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if (u.startsWith("javascript:"))
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return "about:blank";
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return url;
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}

‎javascript/ql/test/query-tests/Security/CWE-020/IncompleteUrlSchemeCheck.qlref‎

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Security/CWE-020/IncompleteUrlSchemeCheck.ql

‎javascript/ql/test/query-tests/Security/CWE-020/IncompleteUrlSchemeCheckGood.js‎

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function sanitizeUrl(url) {
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let u = decodeURI(url).trim().toLowerCase();
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if (u.startsWith("javascript:") || u.startsWith("data:") || u.startsWith("vbscript:"))
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return "about:blank";
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return url;
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}

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