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Response snapshot Oct 27, 2026, 00:02 UTC

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VulnerabilityCVE-2026-112958

ApostropheCMS: Stored XSS via Unescaped Widget Style Attribute Serialization

ApostropheCMS widget styles support project-defined schema fields. If a project defines a free-form `string` style field with a CSS `property` and no selector, an editor-controlled value is rendered as an inline CSS declaration.

Published Updated

At a glance

Exploited
Not known
Severity
5.4 Medium (CVSS 3.1)
Chance of exploitation
0.3% in the next 30 days
Sources
1 source

What to do

GitHub lists first patched versions: apostrophe: 4.34.0. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-7jg5-frgc-c67w (opens a new tab)

What happened

## Summary

ApostropheCMS widget styles support project-defined schema fields. If a project defines a free-form `string` style field with a CSS `property` and no selector, an editor-controlled value is rendered as an inline CSS declaration. The resulting declaration is then inserted into the widget wrapper's `style="..."` attribute without HTML-attribute escaping.

An attacker who can edit the widget can include a double quote in the style value, terminate the `style` attribute, and inject new HTML event-handler attributes. The payload is stored with the widget and executes in the Apostrophe site origin whenever the affected published page is rendered.

This is a sibling of CVE-2026-33889 / `GHSA-97v6-998m-fp4g`. The earlier issue escaped from a ` ` element through a malicious color value. This variant reaches a different sink related to the automatically generated widget wrapper's inline `style` and `class` attributes.

Continue reading

## Details

### Root Cause 1: Free-form string style values retain HTML metacharacters

The standard string field converter uses `launder.string()` and length validation. This performs type normalization, not output encoding for an HTML attribute context:

[`packages/apostrophe/modules/@apostrophecms/schema/lib/addFieldTypes.js:296-333`](https://github.com/apostrophecms/apostrophe/blob/aa5170c7df9ff9ea5ac2e72a008f12e28dae6ca8/packages/apostrophe/modules/%40apostrophecms/schema/lib/addFieldTypes.js#L296-L333)

```javascript self.addFieldType({ name: 'string', // ... convert(req, field, data, destination) { destination[field.name] = self.apos.launder.string(data[field.name]); destination[field.name] = checkStringLength( destination[field.name], field.min, field.max ); } }); ```

Quotes therefore remain in a value supplied through a style field.

### Root Cause 2: The value is converted into inline CSS without value validation

For a field with `property` but no `selector` or media query, `renderScopedStyles()` selects inline rendering. The generic extractor concatenates the configured property and editor-controlled value:

[`packages/apostrophe/modules/@apostrophecms/styles/ui/apos/universal/render.mjs:171-228`](https://github.com/apostrophecms/apostrophe/blob/aa5170c7df9ff9ea5ac2e72a008f12e28dae6ca8/packages/apostrophe/modules/%40apostrophecms/styles/ui/apos/universal/render.mjs#L171-L228)

[`packages/apostrophe/modules/@apostrophecms/styles/ui/apos/universal/render.mjs:598-647`](https://github.com/apostrophecms/apostrophe/blob/aa5170c7df9ff9ea5ac2e72a008f12e28dae6ca8/packages/apostrophe/modules/%40apostrophecms/styles/ui/apos/universal/render.mjs#L598-L647)

```javascript rule = `${property}: ${normalized.value}${normalized.unit}`;

// ...

if (isInline) { return { css: '', classes: [ ...storage.classes ], inline: stringifyRules(storage.styles, true) }; } ```

For example, the value below becomes part of a `font-family` declaration:

```text serif" tabindex="0" autofocus onfocus="document.body.dataset.inline='executed' ```

### Root Cause 3: Attribute values are serialized without HTML escaping

`getWidgetAttributes()` places the inline CSS into an attribute tuple, then concatenates every tuple into `key="value"` without encoding `&`, ` `, `'`, or `"`:

[`packages/apostrophe/modules/@apostrophecms/styles/lib/methods.js:251-322`](https://github.com/apostrophecms/apostrophe/blob/aa5170c7df9ff9ea5ac2e72a008f12e28dae6ca8/packages/apostrophe/modules/%40apostrophecms/styles/lib/methods.js#L251-L322)

```javascript if (styleParts.length) { attrs.push( [ 'style', `${styleParts.join(';')};` ] ); }

if (options.asObject) { return Object.fromEntries(attrs); }

return attrs .map(([ key, value ]) => `${key}="${value}"`) .join(' '); ```

The same raw serializer also makes a project-defined free-form `string` style with `class: true` a potential sibling path, because the string is added to `classes` and later serialized into `class="..."`. The inline-property path was the path dynamically verified.

### Root Cause 4: The unsafe string is used by the automatic public wrapper

Styled widgets use `getWidgetAttributes()` to create a wrapper around the rendered widget:

[`packages/apostrophe/modules/@apostrophecms/widget-type/index.js:448-457`](https://github.com/apostrophecms/apostrophe/blob/aa5170c7df9ff9ea5ac2e72a008f12e28dae6ca8/packages/apostrophe/modules/%40apostrophecms/widget-type/index.js#L448-L457)

```javascript if (hasStyles && self.options.stylesWrapper !== false) { const styles = self.apos.styles.prepareWidgetStyles(widget); const styleTag = self.apos.styles .getWidgetElements(styles, { scene: req.scene }); const wrapperAttrs = self.apos.styles.getWidgetAttributes(styles);

return `${styleTag} ${markup}

`; } ```

Consequently, the injected attribute is present on normal public page renders, not only in the editor UI.

### Why the CVE-2026-33889 defense does not prevent this variant

The sibling advisory led to a defense in `getWidgetElements()` that rewrites ` ` element:

```javascript css = css.replaceAll(' { const { renderScopedStyles } = await import( './packages/apostrophe/modules/@apostrophecms/styles/ui/apos/universal/render.mjs' );

const payload = 'serif" tabindex="0" autofocus ' + 'onfocus="document.body.dataset.inline=\'executed\'';

const styles = renderScopedStyles( [ { name: 'customFont', type: 'string', property: 'font-family' } ], { customFont: payload } );

Object.assign(styles, { styleId: 'audit-inline', widgetId: 'widget-1' });

const attrs = methodsFactory({}, {}).getWidgetAttributes(styles); console.log('inline:', styles.inline); console.log('attributes:', attrs); })(); ```

### Step 4: Observe the unsafe HTML

The current renderer produced:

```text inline: font-family: serif" tabindex="0" autofocus onfocus="document.body.dataset.inline='executed'; ```

The serializer then produced an attribute string equivalent to:

```html id="audit-inline" data-apos-widget-style-wrapper-for="widget-1" data-apos-widget-styl

Affected package ranges reported by GitHub: apostrophe: < 4.34.0

Scores and how they were measured

CVSS base severity

5.4

Version 3.1As of

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

0.3%

Scored Percentile 22.9%

Model and measurement source (opens a new tab)

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-7jg5-frgc-c67w (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-7jg5-frgc-c67w, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  3. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-7jg5-frgc-c67w, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  4. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-7jg5-frgc-c67w, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  5. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-7jg5-frgc-c67w, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  6. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-7jg5-frgc-c67w, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  7. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-7jg5-frgc-c67w, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  8. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-7jg5-frgc-c67w, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  9. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-7jg5-frgc-c67w, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  10. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-7jg5-frgc-c67w, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  11. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-7jg5-frgc-c67w, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  12. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-112958, scored 2026-10-26. This is a model estimate, not proof of exposure.

    Published Checked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 21). ApostropheCMS: Stored XSS via Unescaped Widget Style Attribute Serialization (CVE-2026-112958). https://kevwire.com/record/CVE-2026-112958

MLA

"ApostropheCMS: Stored XSS via Unescaped Widget Style Attribute Serialization (CVE-2026-112958)." KEVWire, 21 Oct. 2026, kevwire.com/record/CVE-2026-112958.

Chicago

KEVWire. "ApostropheCMS: Stored XSS via Unescaped Widget Style Attribute Serialization (CVE-2026-112958)." Last modified October 21, 2026. https://kevwire.com/record/CVE-2026-112958.

Evidence summary (plain text)

ApostropheCMS: Stored XSS via Unescaped Widget Style Attribute Serialization (Oct 21, 2026).
ApostropheCMS widget styles support project-defined schema fields. If a project defines a free-form `string` style field with a CSS `property` and no selector, an editor-controlled value is rendered as an inline CSS declaration. The resulting declaration is then inserted into the widget wrapper's `style="..."` attribute without HTML-attribute escaping.

An attacker who can edit the widget can include a double quote in the style value, terminate the `style` attribute, and inject new HTML event-handler attributes. The payload is stored with the widget and executes in the Apostrophe site origin whenever the affected published page is rendered.
CVSS 5.4 (version 3.1; evidence as of Oct 21, 2026; https://github.com/advisories/GHSA-7jg5-frgc-c67w).
EPSS 0.3% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-112958&date=2026-10-26).
Sources:
GitHub-reviewed advisory GHSA-7jg5-frgc-c67w: https://github.com/advisories/GHSA-7jg5-frgc-c67w
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMlQxNTo1Mjo1NlrOAAfxiA%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMlQxNDowNjoxNFrOAAfxZw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMlQwODoyNzoyM1rOAAYp9A%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMTozNTo1OFrOAAfwCQ%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMTozMDoxM1rOAAfv2A%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMToyODowOVrOAAfv1g%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMToyNDoyMFrOAAfv1Q%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMDo0NTowN1rOAAfvzQ%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMDozMDoyNlrOAAfvxw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMDowMzo1N1rOAAfvxQ%3D%3D
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-112958&date=2026-10-26
Record ID: CVE-2026-112958.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 26, 2026, 19:40 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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