### Summary jodit's built-in `clean-html` sanitizer can be bypassed by a MathML/`<style>` carrier that hides a dangerous element from the sanitizer's element walk, so a no-interaction event handler survives into the editor value. When an application supplies attacker-influenced HTML to the editor's value-set or insertion paths, the sanitized output still contains a live `<img ... onload=...>` (or another non-`onerror` handler such as `onfocus`). A consumer that renders that output (`element.innerHTML = editor.value`) executes the handler with no user interaction. This is a stored cross-site scripting vulnerability, confirmed live on the shipped `es2021/jodit.min.js` for 4.12.25 and the latest 4.12.27 (in Chromium via a client-side `innerHTML` consumer, and in Firefox via server-rendered / document-context output; see the cross-browser note under Proof of concept). ### Details The bypass exploits the order in which `clean-html` parses, walks, and re-serializes the value. 1. On the value-set path, the `clean-html` plugin handles `:beforeSetNativeEditorValue` (`src/plugins/clean-html/clean-html.ts:116`), parsing the value into an inert document: `sandBox.innerHTML = data.value`. 2. In that parse, the source nesting `math > mtext > table > mglyph > style` triggers MathML text-integration-point and foster-parenting rules: the `<img>` is parsed as text inside `<style>` (rawtext), not as an element. The `<table>` is foster-parented out, and the `<mglyph>` MathML text-integration point governs the namespace, so the `<img>` never becomes an element node in this parse. 3. That value-set sanitizer is `safeHTML` (`src/core/helpers/html/safe-html.ts:24`); it walks the tree but acts on elements only (the `Dom.isElement` gate at `:39`) and runs against the parse-1 `sandBox`, in which the `<img>` is rawtext, not an element. So `removeAllEventAttributes` (the full `on*` strip at `safe-html.ts:76`) has no element to clean and the handler passes through. The `onBeforeSetNativeEditorValue` handler runs `safeHTML` on that parse-1 tree both before and after it captures the value, so neither pass ever sees the `<img>` as an element. 4. The captured value (`data.value = sandBox.innerHTML`) is then assigned to the editable, a second parse, which hoists the `<img>` out of `<style>` and into the HTML namespace as a live element with its handler intact. The serialize-reparse moves the element across the tree and across namespaces: ``` BEFORE - parse 1 (sandBox): the <img> is <style> text <math> [MathML] <mtext> [MathML] <mglyph> [HTML] integration point: content parses as HTML <style> [HTML] text "<img ... onload=...>" <-- <img> is RAWTEXT, not an element <table> [HTML] AFTER - editor.value (re-parsed): the <img> is hoisted OUT of <style>, live <p> [HTML] <math> [MathML] <mtext> [MathML] <mglyph> [MathML] <style> [MathML] (now empty) <img> [HTML] <-- hoisted out, HTML namespace, LIVE -> its handler fires <table> [HTML] ``` 5. `editor.value` now carries that live element. The value-set pass (Steps 1-4) only walked the parse-1 `sandBox` and never sees it; the other sanitizer, the on-change visitor (`visitNodeWalker` via a `LazyWalker`, `clean-html.ts:56`/`:70`), does reach the hoisted element, but its `sanitizeAttributes` filter calls `sanitizeHTMLElement` (`safe-html.ts:139`), which strips `onerror` only - it never reads the `removeEventAttributes` flag `sanitizeAttributes` passes it (`sanitize-attributes.ts:30`), so it never runs the full `on*` strip. So `onload`, `onfocus`, and every other non-`onerror` handler is never removed and persists in `editor.value` permanently. (`onerror` is the one handler the cleaner removes, but only after a ~300ms window in which it too fires.) The two code points (jodit 4.12.27): ```js // 1. clean-html.ts onBeforeSetNativeEditorValue - the SYNCHRONOUS value-set pass runs on the parse-1 sandBox: sandBox.innerHTML = data.value; // :128 parse 1: the carrier hides the element as <style> rawtext this.j.e.fire('safeHTML', sandBox); // :129 safeHTML element-walk misses the rawtext element data.value = sandBox.innerHTML; // :130 value captured; re-parsing it into the editable hoists the element live safeHTML(sandBox, { safeJavaScriptLink: true, removeOnError: true }); // :131 re-runs on the SAME parse-1 sandBox, never on the captured value // 2. the ASYNC on-change filter (LazyWalker) reaches the hoisted element, but only strips onerror: sanitizeHTMLElement(nodeElm, { /* ... */ removeEventAttributes: opts.removeEventAttributes }); // sanitize-attributes.ts:30 - passes the full-strip flag export function sanitizeHTMLElement(elm, { safeJavaScriptLink, removeOnError } = { /* ... */ }) { // safe-html.ts:139 - never destructures removeEventAttributes if (removeOnError && elm.hasAttribute('onerror')) attr(elm, 'onerror', null); // onerror ONLY; onload / onfocus / ... are left live } ``` All four layers are required: removing any of `math` + the integration point, `table`, the `mglyph` slot, or the rawtext element makes jodit strip the handler (substitutes per slot are under Carrier variants). The four-layer carrier is required only on 4.11.2 and later. jodit 4.11.2 added `cleanHTML.removeEventAttributes` (the value-set full `on*` strip); before it (all 3.x and 4.0 through 4.10.x) the sanitizer only ever removed `onerror`, so on those versions a plain non-`onerror` handler such as `<img ... onload=...>` survives `editor.value` directly with no carrier (live-confirmed on 3.24.9, 4.0.1, 4.2.27). On 4.11.2 and later, the value-set walk strips the bare handler, so the carrier is needed to hide it as `<style>` rawtext past that walk; and because the on-change cleaner removes only `onerror` (Step 5), a non-`onerror` hoisted handler survives across the whole range. The bypass is not specific to the value setter. The same carrier survives clean-html through `editor.value = X`, `editor.setEditorValue(X)`, and `editor.s.insertHTML(X)` (the API jodit's own documentation uses for plugins and custom buttons). This is distinct from jodit's known XSS advisories: CVE-2023-42399 (GHSA-95xr-cq6h-vwr3) is an `iframe[src]` URL-scheme issue fixed in a 4.0.0 beta, and CVE-2022-23461 (GHSA-42hx-vrxx-5r6v) is a paste-from-Word `onerror` desanitization in `<= 3.24.2`. Neither involves this parse-1 rawtext-hoist mechanism, and a search of the issue tracker for mglyph / mathml / mutation / "value xss" finds no prior report. ### Proof of concept Default configuration. Assign the payload, read it back, render it the way a consumer would: ```js const editor = Jodit.make('#editor'); editor.value = '<math><mtext><table><mglyph><style><img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" onload=alert(document.domain)></style></mglyph></table></mtext></math>'; // editor.value (the sanitized, stored output) now contains a live handler, and it persists (onload, like any // non-onerror handler, is not removed by jodit's on-change cleaner): // <p><math><mtext><mglyph><style></style></mglyph> // <img src="data:image/gif;base64,R0lGOD...AAIBRAA7" onload="alert(document.domain)"> // <table></table></mtext></math></p> document.getElementById('view').innerHTML = editor.value; // a consumer renders the saved value // -> the 1x1 gif loads, onload fires alert(document.domain), no interaction ``` Cross-browser: `editor.value` carries the hoisted live `<img>` in both Blink and Gecko, but the consumer's parse mode decides execution. Chromium fires it under both client-side `element.innerHTML` and document parsing; Firefox fires it only under document parsing (server-side rendering, `document.write`, `<iframe srcdoc>`), because under `innerHTML` Gecko leaves the `<img>` in the MathML namespace, inert. No iframe is required: a plain `innerHTML` consumer suffices in Chromium, any server-rendered consumer in Firefox. Positive control, same run: a plain `<img src=x onerror=alert(1)>`, a plain `<img onfocus=alert(1) autofocus tabindex=1>`, and a plain `<svg onload=alert(1)>` are all stripped by the synchronous value-set pass to harmless output, proving clean-html is active; the same handlers pass through only when carrier-hidden as `<style>` rawtext, so the contrast isolates the rawtext-hiding step. (A plain `<script>` is a separate case - the value-set pass does not remove tags; only the async on-change cleaner removes it ~300ms later - so it is not part of this synchronous control.) Carrier variants: three of the four layers accept substitutes: the MathML text-integration point (`mtext` / `mi` / `ms` / `mn` / `mo`), the integration-point child (`mglyph` / `malignmark`), and the rawtext element (`style` / `xmp` / `noembed` / `script` / `plaintext`; `title` / `textarea` / `noscript` do not work). `math` and `table` have no working substitute. The hidden element is not limited to `<img>`, and any non-`onerror` handler persists permanently. Element-name blocklisting will not close this. ### Impact Stored XSS with no user interaction, in the default configuration, on the input paths that jodit's own `clean-html` is responsible for sanitizing. jodit's own test suite asserts this is a sanitization boundary: `src/plugins/clean-html/clean-html.test.js` asserts that `editor.value = '<p>test <img src="" onerror="alert(111)" alt=""></p>'` sanitizes to `<p>test <img src="" alt=""></p>` (the `onerror` removed) under the default config. The carrier in this report passes that same default-config sanitizer yet keeps the handler live, defeating the asserted guarantee. A prior fix in 4.12.21 addressed a stored XSS premised on an application re-rendering `editor.value` as trusted HTML, so this threat model is maintainer-acknowledged. Precondition: an attacker can place HTML into the editor (a content-submission role) and the editor output is later rendered. Any integration binding `value` to application state in jodit-react, loading a previously stored document, or inserting content via a plugin/button will execute attacker script in the victim's page. ### Suggested fix Remove the gadget element at the source rather than re-sanitizing the output. A re-sanitize loop does not close this: nesting the carrier inside itself surfaces one level per parse, so one extra pass is bypassed at depth 2, and any fixed cap N is out-nested at depth N+2 (depth generalizes trivially). The robust fix is to drop any HTML-namespace element smuggled inside `<math>`/`<svg>` outside a spec integration point (`<foreignObject>`, `<annotation-xml>`, `<desc>`, `<title>`) during the element walk, the same approach DOMPurify's `_checkValidNamespace` uses. This is one pass and depth-independent. It must run on both entry points: the synchronous value-set `safeHTML` pass and the on-change walker (which does not call `safeHTML`). A regression test asserting that no `on*` survives a round-trip through `editor.value`, including the nested-carrier case, locks it in.

### Summary jodit's built-in `clean-html` sanitizer can be bypassed by a MathML/`<style>` carrier that hides a dangerous element from the sanitizer's element walk, so a no-interaction event handler survives into the editor value. When an application supplies attacker-influenced HTML to the editor's value-set or insertion paths, the sanitized output still contains a live `<img ... onload=...>` (or another non-`onerror` handler such as `onfocus`). A consumer that renders that output (`element.innerHTML = editor.value`) executes the handler with no user interaction. This is a stored cross-site scripting vulnerability, confirmed live on the shipped `es2021/jodit.min.js` for 4.12.25 and the latest 4.12.27 (in Chromium via a client-side `innerHTML` consumer, and in Firefox via server-rendered / document-context output; see the cross-browser note under Proof of concept). ### Details The bypass exploits the order in which `clean-html` parses, walks, and re-serializes the value. 1. On the value-set path, the `clean-html` plugin handles `:beforeSetNativeEditorValue` (`src/plugins/clean-html/clean-html.ts:116`), parsing the value into an inert document: `sandBox.innerHTML = data.value`. 2. In that parse, the source nesting `math > mtext > table > mglyph > style` triggers MathML text-integration-point and foster-parenting rules: the `<img>` is parsed as text inside `<style>` (rawtext), not as an element. The `<table>` is foster-parented out, and the `<mglyph>` MathML text-integration point governs the namespace, so the `<img>` never becomes an element node in this parse. 3. That value-set sanitizer is `safeHTML` (`src/core/helpers/html/safe-html.ts:24`); it walks the tree but acts on elements only (the `Dom.isElement` gate at `:39`) and runs against the parse-1 `sandBox`, in which the `<img>` is rawtext, not an element. So `removeAllEventAttributes` (the full `on*` strip at `safe-html.ts:76`) has no element to clean and the handler passes through. The `onBeforeSetNativeEditorValue` handler runs `safeHTML` on that parse-1 tree both before and after it captures the value, so neither pass ever sees the `<img>` as an element. 4. The captured value (`data.value = sandBox.innerHTML`) is then assigned to the editable, a second parse, which hoists the `<img>` out of `<style>` and into the HTML namespace as a live element with its handler intact. The serialize-reparse moves the element across the tree and across namespaces: ``` BEFORE - parse 1 (sandBox): the <img> is <style> text <math> [MathML] <mtext> [MathML] <mglyph> [HTML] integration point: content parses as HTML <style> [HTML] text "<img ... onload=...>" <-- <img> is RAWTEXT, not an element <table> [HTML] AFTER - editor.value (re-parsed): the <img> is hoisted OUT of <style>, live <p> [HTML] <math> [MathML] <mtext> [MathML] <mglyph> [MathML] <style> [MathML] (now empty) <img> [HTML] <-- hoisted out, HTML namespace, LIVE -> its handler fires <table> [HTML] ``` 5. `editor.value` now carries that live element. The value-set pass (Steps 1-4) only walked the parse-1 `sandBox` and never sees it; the other sanitizer, the on-change visitor (`visitNodeWalker` via a `LazyWalker`, `clean-html.ts:56`/`:70`), does reach the hoisted element, but its `sanitizeAttributes` filter calls `sanitizeHTMLElement` (`safe-html.ts:139`), which strips `onerror` only - it never reads the `removeEventAttributes` flag `sanitizeAttributes` passes it (`sanitize-attributes.ts:30`), so it never runs the full `on*` strip. So `onload`, `onfocus`, and every other non-`onerror` handler is never removed and persists in `editor.value` permanently. (`onerror` is the one handler the cleaner removes, but only after a ~300ms window in which it too fires.) The two code points (jodit 4.12.27): ```js // 1. clean-html.ts onBeforeSetNativeEditorValue - the SYNCHRONOUS value-set pass runs on the parse-1 sandBox: sandBox.innerHTML = data.value; // :128 parse 1: the carrier hides the element as <style> rawtext this.j.e.fire('safeHTML', sandBox); // :129 safeHTML element-walk misses the rawtext element data.value = sandBox.innerHTML; // :130 value captured; re-parsing it into the editable hoists the element live safeHTML(sandBox, { safeJavaScriptLink: true, removeOnError: true }); // :131 re-runs on the SAME parse-1 sandBox, never on the captured value // 2. the ASYNC on-change filter (LazyWalker) reaches the hoisted element, but only strips onerror: sanitizeHTMLElement(nodeElm, { /* ... */ removeEventAttributes: opts.removeEventAttributes }); // sanitize-attributes.ts:30 - passes the full-strip flag export function sanitizeHTMLElement(elm, { safeJavaScriptLink, removeOnError } = { /* ... */ }) { // safe-html.ts:139 - never destructures removeEventAttributes if (removeOnError && elm.hasAttribute('onerror')) attr(elm, 'onerror', null); // onerror ONLY; onload / onfocus / ... are left live } ``` All four layers are required: removing any of `math` + the integration point, `table`, the `mglyph` slot, or the rawtext element makes jodit strip the handler (substitutes per slot are under Carrier variants). The four-layer carrier is required only on 4.11.2 and later. jodit 4.11.2 added `cleanHTML.removeEventAttributes` (the value-set full `on*` strip); before it (all 3.x and 4.0 through 4.10.x) the sanitizer only ever removed `onerror`, so on those versions a plain non-`onerror` handler such as `<img ... onload=...>` survives `editor.value` directly with no carrier (live-confirmed on 3.24.9, 4.0.1, 4.2.27). On 4.11.2 and later, the value-set walk strips the bare handler, so the carrier is needed to hide it as `<style>` rawtext past that walk; and because the on-change cleaner removes only `onerror` (Step 5), a non-`onerror` hoisted handler survives across the whole range. The bypass is not specific to the value setter. The same carrier survives clean-html through `editor.value = X`, `editor.setEditorValue(X)`, and `editor.s.insertHTML(X)` (the API jodit's own documentation uses for plugins and custom buttons). This is distinct from jodit's known XSS advisories: CVE-2023-42399 (GHSA-95xr-cq6h-vwr3) is an `iframe[src]` URL-scheme issue fixed in a 4.0.0 beta, and CVE-2022-23461 (GHSA-42hx-vrxx-5r6v) is a paste-from-Word `onerror` desanitization in `<= 3.24.2`. Neither involves this parse-1 rawtext-hoist mechanism, and a search of the issue tracker for mglyph / mathml / mutation / "value xss" finds no prior report. ### Proof of concept Default configuration. Assign the payload, read it back, render it the way a consumer would: ```js const editor = Jodit.make('#editor'); editor.value = '<math><mtext><table><mglyph><style><img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" onload=alert(document.domain)></style></mglyph></table></mtext></math>'; // editor.value (the sanitized, stored output) now contains a live handler, and it persists (onload, like any // non-onerror handler, is not removed by jodit's on-change cleaner): // <p><math><mtext><mglyph><style></style></mglyph> // <img src="data:image/gif;base64,R0lGOD...AAIBRAA7" onload="alert(document.domain)"> // <table></table></mtext></math></p> document.getElementById('view').innerHTML = editor.value; // a consumer renders the saved value // -> the 1x1 gif loads, onload fires alert(document.domain), no interaction ``` Cross-browser: `editor.value` carries the hoisted live `<img>` in both Blink and Gecko, but the consumer's parse mode decides execution. Chromium fires it under both client-side `element.innerHTML` and document parsing; Firefox fires it only under document parsing (server-side rendering, `document.write`, `<iframe srcdoc>`), because under `innerHTML` Gecko leaves the `<img>` in the MathML namespace, inert. No iframe is required: a plain `innerHTML` consumer suffices in Chromium, any server-rendered consumer in Firefox. Positive control, same run: a plain `<img src=x onerror=alert(1)>`, a plain `<img onfocus=alert(1) autofocus tabindex=1>`, and a plain `<svg onload=alert(1)>` are all stripped by the synchronous value-set pass to harmless output, proving clean-html is active; the same handlers pass through only when carrier-hidden as `<style>` rawtext, so the contrast isolates the rawtext-hiding step. (A plain `<script>` is a separate case - the value-set pass does not remove tags; only the async on-change cleaner removes it ~300ms later - so it is not part of this synchronous control.) Carrier variants: three of the four layers accept substitutes: the MathML text-integration point (`mtext` / `mi` / `ms` / `mn` / `mo`), the integration-point child (`mglyph` / `malignmark`), and the rawtext element (`style` / `xmp` / `noembed` / `script` / `plaintext`; `title` / `textarea` / `noscript` do not work). `math` and `table` have no working substitute. The hidden element is not limited to `<img>`, and any non-`onerror` handler persists permanently. Element-name blocklisting will not close this. ### Impact Stored XSS with no user interaction, in the default configuration, on the input paths that jodit's own `clean-html` is responsible for sanitizing. jodit's own test suite asserts this is a sanitization boundary: `src/plugins/clean-html/clean-html.test.js` asserts that `editor.value = '<p>test <img src="" onerror="alert(111)" alt=""></p>'` sanitizes to `<p>test <img src="" alt=""></p>` (the `onerror` removed) under the default config. The carrier in this report passes that same default-config sanitizer yet keeps the handler live, defeating the asserted guarantee. A prior fix in 4.12.21 addressed a stored XSS premised on an application re-rendering `editor.value` as trusted HTML, so this threat model is maintainer-acknowledged. Precondition: an attacker can place HTML into the editor (a content-submission role) and the editor output is later rendered. Any integration binding `value` to application state in jodit-react, loading a previously stored document, or inserting content via a plugin/button will execute attacker script in the victim's page. ### Suggested fix Remove the gadget element at the source rather than re-sanitizing the output. A re-sanitize loop does not close this: nesting the carrier inside itself surfaces one level per parse, so one extra pass is bypassed at depth 2, and any fixed cap N is out-nested at depth N+2 (depth generalizes trivially). The robust fix is to drop any HTML-namespace element smuggled inside `<math>`/`<svg>` outside a spec integration point (`<foreignObject>`, `<annotation-xml>`, `<desc>`, `<title>`) during the element walk, the same approach DOMPurify's `_checkValidNamespace` uses. This is one pass and depth-independent. It must run on both entry points: the synchronous value-set `safeHTML` pass and the on-change walker (which does not call `safeHTML`). A regression test asserting that no `on*` survives a round-trip through `editor.value`, including the nested-carrier case, locks it in.