@nuxtjs/mdc: the URL sanitizer misses SVG xlink:href and data:text/html, allowing XSS from untrusted markdown at the default configuration

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

MDC is a tool to take regular Markdown and write documents interacting deeply with a Vue component. Prior to 0.22.1, @nuxtjs/mdc uses parseMarkdown with allowDangerousHtml enabled by default and relies on validateProps, validateProp, and unsafeLinkPrefix to remove executable URLs from untrusted Markdown. validateProp checks only attributes named href or src, allowing an SVG xlink:href value represented as xLinkHref to retain a javascript: URL that executes in the page origin when selected. The data:text/html denylist entries are also compared against url.protocol, which is only data:, so an iframe src containing data:text/html survives sanitization and executes in an opaque origin when loaded. Plain href javascript: URLs, srcdoc, object, script, and base elements are already blocked, making these two paths specific sibling gaps in the sanitizer. This issue is fixed in version 0.22.1.

Source published

16 Sep 2026 14:25:47 UTC

Source modified

18 Sep 2026 17:54:37 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · 8.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N

MDC is a tool to take regular Markdown and write documents interacting deeply with a Vue component. Prior to 0.22.1, @nuxtjs/mdc uses parseMarkdown with allowDangerousHtml enabled by default and relies on validateProps, validateProp, and unsafeLinkPrefix to remove executable URLs from untrusted Markdown. validateProp checks only attributes named href or src, allowing an SVG xlink:href value represented as xLinkHref to retain a javascript: URL that executes in the page origin when selected. The data:text/html denylist entries are also compared against url.protocol, which is only data:, so an iframe src containing data:text/html survives sanitization and executes in an opaque origin when loaded. Plain href javascript: URLs, srcdoc, object, script, and base elements are already blocked, making these two paths specific sibling gaps in the sanitizer. This issue is fixed in version 0.22.1.

Source published

Sep 16, 2026, 2:25:47 PM (timezone not stated)

Source modified

Sep 18, 2026, 5:54:37 PM (timezone not stated)

Observed here

11 Nov 2026 15:06:52 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 3.1 · 8.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N

MDC is a tool to take regular Markdown and write documents interacting deeply with a Vue component. Prior to 0.22.1, @nuxtjs/mdc uses parseMarkdown with allowDangerousHtml enabled by default and relies on validateProps, validateProp, and unsafeLinkPrefix to remove executable URLs from untrusted Markdown. validateProp checks only attributes named href or src, allowing an SVG xlink:href value represented as xLinkHref to retain a javascript: URL that executes in the page origin when selected. The data:text/html denylist entries are also compared against url.protocol, which is only data:, so an iframe src containing data:text/html survives sanitization and executes in an opaque origin when loaded. Plain href javascript: URLs, srcdoc, object, script, and base elements are already blocked, making these two paths specific sibling gaps in the sanitizer. This issue is fixed in version 0.22.1.

Source published

16 Sep 2026 15:17:40 UTC

Source modified

24 Sep 2026 21:25:27 UTC

Observed here

25 Oct 2026 15:18:45 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 8.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N

## Summary `@nuxtjs/mdc` renders untrusted markdown (including raw HTML) to a Vue component tree. Across two prior advisories it added a URL/attribute sanitizer to block dangerous links in that HTML: `validateProps` / `validateProp` and an `unsafeLinkPrefix` deny-list (`dist/runtime/parser/utils/props.js`). The sanitizer runs at parse time (`dist/runtime/parser/compiler.js`) and `parseMarkdown` enables raw HTML by default (`allowDangerousHtml: true`, `dist/runtime/parser/options.js`), so the sanitizer is the only barrier and it applies with no configuration required. Two sibling vectors bypass that sanitizer at the default configuration: 1. SVG anchor `xlink:href`. `validateProp` only scheme-checks attributes named exactly `href` or `src`: ``` if (attribute === "href" || attribute === "src") return isAnchorLinkAllowed(value); return true; ``` An `xlink:href` (parsed to the hast property `xLinkHref`) is neither, so a `javascript:` URL on an SVG `<a>` is passed through. The renderer maps the property back to the real attribute (`MDCRenderer.vue`: `find(html, "xLinkHref").attribute` is `xlink:href`), so the output element is `<a xlink:href="javascript:...">`. Clicking it runs the script in the page origin. Plain `<a href="javascript:...">` is correctly stripped, which is what makes this the un-patched sibling. 2. `<iframe src="data:text/html,...">`. `data:text/html` is present in `unsafeLinkPrefix`, but the check compares it against `url.protocol`: ``` if (unsafeLinkPrefix.some((prefix) => url.protocol.toLowerCase().startsWith(prefix))) return false; ``` For any data URI `url.protocol` is just `"data:"`, so `"data:".startsWith("data:text/html")` is always false. Every `data:text/*` entry in the deny-list is therefore dead code, and `<iframe src="data:text/html,<script>...</script>">` is allowed (iframe is not in the render-time `dangerousTags`, which is only `["script","base"]`). The framed document executes script in an opaque origin. For contrast, `srcdoc` and `object` are blocked, so this is a precise gap rather than a general absence of filtering. ## Reproduction I will attach the zip file for POC, you can simply extract and run `./poc.sh` to install mdc and show the poc in the html file. [nuxtjs-mdc-xss_poc.zip](https://github.com/user-attachments/files/29175603/nuxtjs-mdc-xss_poc.zip) Two zero-argument checks: 1. `sh poc/poc.sh` installs `@nuxtjs/mdc` and runs `parseMarkdown` (the documented API) at default. It shows the parsed tree retains `a { xLinkHref: "javascript:..." }` and `iframe { src: "data:text/html,..." }`, while the control payloads `href="javascript:..."` and `srcdoc=...` are removed by the sanitizer. This isolates the sanitizer bypass deterministically. 2. `poc/poc.sh` also serves `poc/poc.html` over http (data: iframes and javascript: links are restricted under the file:// origin, so http is used). Open the printed URL and click the blue SVG link. The page contains the exact DOM the renderer produces for those parsed nodes; clicking the SVG link executes script in the page origin (same-origin), and the data:text/html iframe executes on load. The page prints VULNERABLE for each that fires. Both vectors were confirmed executing in a current Chromium build: the SVG `xlink:href` link runs script in the document origin on click, and the data:text/html iframe runs script on load. ## Suggested fix In `validateProp`, scheme-check `xlink:href` (and the hast `xLinkHref`) the same way as `href`/`src`. In `isAnchorLinkAllowed`, compare the dangerous MIME-typed entries against the full URL (or `href`), not against `url.protocol`, so `data:text/html` is actually matched; or add `iframe` to the render-time dangerous-tag set / restrict iframe `src` schemes.

Source published

16 Sep 2026 22:14:01 UTC

Source modified

16 Sep 2026 22:30:08 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N

Publisher rating · HIGH