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JS: Handle default 'content-type' header in Response() objects #20918

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cc7bf4e
JS: Handle default 'content-type' header in Response() objects
asgerf Nov 26, 2025
818f481
JS: Change note
asgerf Nov 26, 2025
7c0243f
Apply suggestions from code review
asgerf Nov 27, 2025
bde983b
Update 2025-11-26-response-default-content-type.md
asgerf Nov 27, 2025
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11 changes: 10 additions & 1 deletion javascript/ql/lib/semmle/javascript/frameworks/WebResponse.qll
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Original file line number Diff line number Diff line change
Expand Up @@ -45,6 +45,10 @@ private class ResponseArgumentHeaders extends Http::HeaderDefinition {
ResponseArgumentHeaders() {
headerNode = response.getParameter(1).getMember("headers") and
this = headerNode.asSink()
or
not exists(response.getParameter(1).getMember("headers")) and
headerNode = API::root() and // just bind 'headerNode' to something
this = response
}

ResponseCall getResponse() { result = response }
Expand Down Expand Up @@ -80,9 +84,14 @@ private class ResponseArgumentHeaders extends Http::HeaderDefinition {

override predicate defines(string headerName, string headerValue) {
this.getHeaderNode(headerName).getAValueReachingSink().getStringValue() = headerValue
or
// If no 'content-type' header is defined, a default one is sent in the HTTP response.
not exists(this.getHeaderNode("content-type")) and
headerName = "content-type" and
headerValue = "text/plain;charset=utf-8"
}

override string getAHeaderName() { exists(this.getHeaderNode(result)) }
override string getAHeaderName() { exists(this.getHeaderNode(result)) or result = "content-type" }

override Http::RouteHandler getRouteHandler() { none() }
}
Expand Down
5 changes: 5 additions & 0 deletions javascript/ql/src/change-notes/2025-11-26-response-default-content-type.md
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@@ -0,0 +1,5 @@
---
category: minorAnalysis
---
* `new Response(x)` is no longer seen as a reflected XSS sink when no `content-type` header
is set, since the content type defaults to `text/plain`.
15 changes: 0 additions & 15 deletions javascript/ql/test/query-tests/Security/CWE-079/ReflectedXss/ReflectedXss.expected
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Original file line number Diff line number Diff line change
Expand Up @@ -50,15 +50,10 @@
| partial.js:28:14:28:18 | x + y | partial.js:31:47:31:53 | req.url | partial.js:28:14:28:18 | x + y | Cross-site scripting vulnerability due to a $@. | partial.js:31:47:31:53 | req.url | user-provided value |
| partial.js:37:14:37:18 | x + y | partial.js:40:43:40:49 | req.url | partial.js:37:14:37:18 | x + y | Cross-site scripting vulnerability due to a $@. | partial.js:40:43:40:49 | req.url | user-provided value |
| promises.js:6:25:6:25 | x | promises.js:5:44:5:57 | req.query.data | promises.js:6:25:6:25 | x | Cross-site scripting vulnerability due to a $@. | promises.js:5:44:5:57 | req.query.data | user-provided value |
| response-object.js:9:18:9:21 | data | response-object.js:7:18:7:25 | req.body | response-object.js:9:18:9:21 | data | Cross-site scripting vulnerability due to a $@. | response-object.js:7:18:7:25 | req.body | user-provided value |
| response-object.js:10:18:10:21 | data | response-object.js:7:18:7:25 | req.body | response-object.js:10:18:10:21 | data | Cross-site scripting vulnerability due to a $@. | response-object.js:7:18:7:25 | req.body | user-provided value |
| response-object.js:11:18:11:21 | data | response-object.js:7:18:7:25 | req.body | response-object.js:11:18:11:21 | data | Cross-site scripting vulnerability due to a $@. | response-object.js:7:18:7:25 | req.body | user-provided value |
| response-object.js:14:18:14:21 | data | response-object.js:7:18:7:25 | req.body | response-object.js:14:18:14:21 | data | Cross-site scripting vulnerability due to a $@. | response-object.js:7:18:7:25 | req.body | user-provided value |
| response-object.js:17:18:17:21 | data | response-object.js:7:18:7:25 | req.body | response-object.js:17:18:17:21 | data | Cross-site scripting vulnerability due to a $@. | response-object.js:7:18:7:25 | req.body | user-provided value |
| response-object.js:23:18:23:21 | data | response-object.js:7:18:7:25 | req.body | response-object.js:23:18:23:21 | data | Cross-site scripting vulnerability due to a $@. | response-object.js:7:18:7:25 | req.body | user-provided value |
| response-object.js:26:18:26:21 | data | response-object.js:7:18:7:25 | req.body | response-object.js:26:18:26:21 | data | Cross-site scripting vulnerability due to a $@. | response-object.js:7:18:7:25 | req.body | user-provided value |
| response-object.js:34:18:34:21 | data | response-object.js:7:18:7:25 | req.body | response-object.js:34:18:34:21 | data | Cross-site scripting vulnerability due to a $@. | response-object.js:7:18:7:25 | req.body | user-provided value |
| response-object.js:38:18:38:21 | data | response-object.js:7:18:7:25 | req.body | response-object.js:38:18:38:21 | data | Cross-site scripting vulnerability due to a $@. | response-object.js:7:18:7:25 | req.body | user-provided value |
| tst2.js:7:12:7:12 | p | tst2.js:6:9:6:9 | p | tst2.js:7:12:7:12 | p | Cross-site scripting vulnerability due to a $@. | tst2.js:6:9:6:9 | p | user-provided value |
| tst2.js:8:12:8:12 | r | tst2.js:6:12:6:15 | q: r | tst2.js:8:12:8:12 | r | Cross-site scripting vulnerability due to a $@. | tst2.js:6:12:6:15 | q: r | user-provided value |
| tst2.js:18:12:18:12 | p | tst2.js:14:9:14:9 | p | tst2.js:18:12:18:12 | p | Cross-site scripting vulnerability due to a $@. | tst2.js:14:9:14:9 | p | user-provided value |
Expand Down Expand Up @@ -184,15 +179,10 @@ edges
| promises.js:5:36:5:42 | [post update] resolve [resolve-value] | promises.js:5:16:5:22 | resolve [Return] [resolve-value] | provenance | |
| promises.js:5:44:5:57 | req.query.data | promises.js:5:36:5:42 | [post update] resolve [resolve-value] | provenance | |
| promises.js:6:11:6:11 | x | promises.js:6:25:6:25 | x | provenance | |
| response-object.js:7:11:7:14 | data | response-object.js:9:18:9:21 | data | provenance | |
| response-object.js:7:11:7:14 | data | response-object.js:10:18:10:21 | data | provenance | |
| response-object.js:7:11:7:14 | data | response-object.js:11:18:11:21 | data | provenance | |
| response-object.js:7:11:7:14 | data | response-object.js:14:18:14:21 | data | provenance | |
| response-object.js:7:11:7:14 | data | response-object.js:17:18:17:21 | data | provenance | |
| response-object.js:7:11:7:14 | data | response-object.js:23:18:23:21 | data | provenance | |
| response-object.js:7:11:7:14 | data | response-object.js:26:18:26:21 | data | provenance | |
| response-object.js:7:11:7:14 | data | response-object.js:34:18:34:21 | data | provenance | |
| response-object.js:7:11:7:14 | data | response-object.js:38:18:38:21 | data | provenance | |
| response-object.js:7:18:7:25 | req.body | response-object.js:7:11:7:14 | data | provenance | |
| tst2.js:6:9:6:9 | p | tst2.js:6:9:6:9 | p | provenance | |
| tst2.js:6:9:6:9 | p | tst2.js:7:12:7:12 | p | provenance | |
Expand Down Expand Up @@ -413,15 +403,10 @@ nodes
| promises.js:6:25:6:25 | x | semmle.label | x |
| response-object.js:7:11:7:14 | data | semmle.label | data |
| response-object.js:7:18:7:25 | req.body | semmle.label | req.body |
| response-object.js:9:18:9:21 | data | semmle.label | data |
| response-object.js:10:18:10:21 | data | semmle.label | data |
| response-object.js:11:18:11:21 | data | semmle.label | data |
| response-object.js:14:18:14:21 | data | semmle.label | data |
| response-object.js:17:18:17:21 | data | semmle.label | data |
| response-object.js:23:18:23:21 | data | semmle.label | data |
| response-object.js:26:18:26:21 | data | semmle.label | data |
| response-object.js:34:18:34:21 | data | semmle.label | data |
| response-object.js:38:18:38:21 | data | semmle.label | data |
| tst2.js:6:9:6:9 | p | semmle.label | p |
| tst2.js:6:9:6:9 | p | semmle.label | p |
| tst2.js:6:12:6:15 | q: r | semmle.label | q: r |
Expand Down
5 changes: 0 additions & 5 deletions ...l/test/query-tests/Security/CWE-079/ReflectedXss/ReflectedXssWithCustomSanitizer.expected
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Original file line number Diff line number Diff line change
Expand Up @@ -48,15 +48,10 @@
| partial.js:28:14:28:18 | x + y | Cross-site scripting vulnerability due to $@. | partial.js:31:47:31:53 | req.url | user-provided value |
| partial.js:37:14:37:18 | x + y | Cross-site scripting vulnerability due to $@. | partial.js:40:43:40:49 | req.url | user-provided value |
| promises.js:6:25:6:25 | x | Cross-site scripting vulnerability due to $@. | promises.js:5:44:5:57 | req.query.data | user-provided value |
| response-object.js:9:18:9:21 | data | Cross-site scripting vulnerability due to $@. | response-object.js:7:18:7:25 | req.body | user-provided value |
| response-object.js:10:18:10:21 | data | Cross-site scripting vulnerability due to $@. | response-object.js:7:18:7:25 | req.body | user-provided value |
| response-object.js:11:18:11:21 | data | Cross-site scripting vulnerability due to $@. | response-object.js:7:18:7:25 | req.body | user-provided value |
| response-object.js:14:18:14:21 | data | Cross-site scripting vulnerability due to $@. | response-object.js:7:18:7:25 | req.body | user-provided value |
| response-object.js:17:18:17:21 | data | Cross-site scripting vulnerability due to $@. | response-object.js:7:18:7:25 | req.body | user-provided value |
| response-object.js:23:18:23:21 | data | Cross-site scripting vulnerability due to $@. | response-object.js:7:18:7:25 | req.body | user-provided value |
| response-object.js:26:18:26:21 | data | Cross-site scripting vulnerability due to $@. | response-object.js:7:18:7:25 | req.body | user-provided value |
| response-object.js:34:18:34:21 | data | Cross-site scripting vulnerability due to $@. | response-object.js:7:18:7:25 | req.body | user-provided value |
| response-object.js:38:18:38:21 | data | Cross-site scripting vulnerability due to $@. | response-object.js:7:18:7:25 | req.body | user-provided value |
| tst2.js:7:12:7:12 | p | Cross-site scripting vulnerability due to $@. | tst2.js:6:9:6:9 | p | user-provided value |
| tst2.js:8:12:8:12 | r | Cross-site scripting vulnerability due to $@. | tst2.js:6:12:6:15 | q: r | user-provided value |
| tst2.js:18:12:18:12 | p | Cross-site scripting vulnerability due to $@. | tst2.js:14:9:14:9 | p | user-provided value |
Expand Down
16 changes: 10 additions & 6 deletions javascript/ql/test/query-tests/Security/CWE-079/ReflectedXss/response-object.js
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Original file line number Diff line number Diff line change
@@ -1,14 +1,14 @@
const express = require('express');

// Note: We're using using express for the taint source in order to to test 'Response'
// Note: We're using express for the taint source in order to test 'Response'
// in isolation from the more complicated http frameworks.

express().get('/foo', (req) => {
const data = req.body; // $ Source

new Response(data); // $ Alert
new Response(data, {}); // $ Alert
new Response(data, { headers: null }); // $ Alert
new Response(data);
new Response(data, {});
new Response(data, { headers: null });

new Response(data, { headers: { 'content-type': 'text/plain'}});
new Response(data, { headers: { 'content-type': 'text/html'}}); // $ Alert
Expand All @@ -23,7 +23,7 @@ express().get('/foo', (req) => {
new Response(data, { headers: headers2 }); // $ Alert

const headers3 = new Headers();
new Response(data, { headers: headers3 }); // $ Alert
new Response(data, { headers: headers3 });

const headers4 = new Headers();
headers4.set('content-type', 'text/plain');
Expand All @@ -35,5 +35,9 @@ express().get('/foo', (req) => {

const headers6 = new Headers();
headers6.set('unrelated-header', 'text/plain');
new Response(data, { headers: headers6 }); // $ Alert
new Response(data, { headers: headers6 });

const headers7 = new Headers();
headers7.set('unrelated-header', 'text/html');
new Response(data, { headers: headers7 });
});