Arbitrary JavaScript Execution via openUrl in @a2ui/web_core

CISA KEV lists vulnerabilities known to be exploited. FIRST EPSS estimates the likelihood of exploitation in the next 30 days. An unavailable score does not mean zero risk.

No exploitation or prediction data is available here for these CVEs. This does not mean they are safe or unlikely to be exploited.

The openUrl function in @a2ui/web_core passes an agent-controlled URL directly to window.open() without validating the URI scheme. A malicious agent can supply a javascript: URI as the url argument of a Button component's functionCall action. When the user clicks the rendered button, arbitrary JavaScript executes in the victim application's browser origin, constituting a stored/reflected XSS with Critical severity. No non-default configuration is required; the Basic Catalog is enabled by default.

Source published

4 Aug 2026 15:36:45 UTC

Source modified

4 Aug 2026 17:43:20 UTC

Saved here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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

Source: cve-program · CVE Program Terms of Use. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 4.0 · 6.1 CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N/E:U

The openUrl function in @a2ui/web_core passes an agent-controlled URL directly to window.open() without validating the URI scheme. A malicious agent can supply a javascript: URI as the url argument of a Button component's functionCall action. When the user clicks the rendered button, arbitrary JavaScript executes in the victim application's browser origin, constituting a stored/reflected XSS with Critical severity. No non-default configuration is required; the Basic Catalog is enabled by default.

Source published

Aug 4, 2026, 3:36:45 PM (timezone not stated)

Source modified

Aug 4, 2026, 5:43:20 PM (timezone not stated)

Saved here

11 Nov 2026 04:39:34 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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

Source: euvd · ENISA EUVD · source terms and attribution apply. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

EUVD CVSS 4.0 · 6.1 CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N/E:U

The openUrl function in @a2ui/web_core passes an agent-controlled URL directly to window.open() without validating the URI scheme. A malicious agent can supply a javascript: URI as the url argument of a Button component's functionCall action. When the user clicks the rendered button, arbitrary JavaScript executes in the victim application's browser origin, constituting a stored/reflected XSS with Critical severity. No non-default configuration is required; the Basic Catalog is enabled by default.

Source published

4 Aug 2026 16:16:20 UTC

Source modified

23 Oct 2026 23:10:00 UTC

Saved here

25 Oct 2026 04:17:26 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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

Source: nvd · NIST NVD usage terms; underlying source attribution retained. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 4.0 · [email protected] · Secondary · 6.1 CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N/E:U/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CVSS 3.1 · [email protected] · Primary · 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

### Summary The `openUrl` function in `@a2ui/web_core` passes an agent-controlled URL directly to `window.open()` without validating the URI scheme. A malicious agent can supply a `javascript:` URI as the `url` argument of a `Button` component's `functionCall` action. When the user clicks the rendered button, arbitrary JavaScript executes in the victim application's browser origin, constituting a stored/reflected XSS. No non-default configuration is required; the Basic Catalog is enabled by default. ### Details The vulnerability exists in the `openUrl` function implementation within the Basic Catalog of `@a2ui/web_core` (commit `23a003248abbf59da6c376ea64ace91d82d209ff`). **Sink** — `renderers/web_core/src/v0_9/basic_catalog/functions/basic_functions.ts:428-430`: ```ts export const OpenUrlImplementation = createFunctionImplementation(OpenUrlApi, args => { if (args.url && typeof window !== 'undefined' && window.open) { window.open(args.url, '_blank'); } }); ``` `window.open` is called unconditionally with the agent-supplied `args.url` value. No scheme allowlist or blocklist is applied. **Insufficient schema validation** — `renderers/web_core/src/v0_9/basic_catalog/functions/basic_functions_api.ts:453-458`: ```ts export const OpenUrlApi = { name: 'openUrl' as const, returnType: 'void' as const, schema: z.object({ url: z.preprocess(v => (v === undefined ? undefined : String(v)), z.string()), }), }; ``` The Zod schema only requires a `string`; `javascript:` URIs pass validation without any rejection. **Full source-to-sink data flow:** 1. `renderers/web_core/src/v0_9/basic_catalog/components/basic_components.ts:356` — `ButtonApi` accepts `action: ActionSchema` (entry point). 2. `renderers/web_core/src/v0_9/schema/common-types.ts:126-130` — `ActionSchema` permits `{ functionCall: FunctionCallSchema }`. 3. `renderers/web_core/src/v0_9/rendering/generic-binder.ts:243-255` — on click, bound action calls `resolveDeepSync` then `dispatchAction`. 4. `renderers/web_core/src/v0_9/rendering/data-context.ts:93-105` — `resolveDynamicValue` detects the `call` key and invokes the named function. 5. `renderers/web_core/src/v0_9/catalog/types.ts:177-186` — catalog invoker runs `fn.schema.parse(rawArgs)` then `fn.execute()`. 6. `renderers/web_core/src/v0_9/basic_catalog/functions/basic_functions_api.ts:453-458` — `OpenUrlApi` validates `url` as `z.string()` only (no scheme check). 7. `renderers/web_core/src/v0_9/basic_catalog/functions/basic_functions.ts:428-430` — **sink**: `window.open(args.url, '_blank')` executes the `javascript:` URI. **All three renderers implemented in the A2UI repository are affected:** - React: `renderers/react/src/v0_9/catalog/basic/components/Button.tsx:33` — `onClick={props.action}` - Lit: `renderers/lit/src/v0_9/catalogs/basic/components/Button.ts:112` — `@click=${() => props.action()}` - Angular: `renderers/angular/src/v0_9/catalog/basic/button.component.ts:103-110` — `handleClick()` → `dataContext.resolveAction` → `dispatchAction` Any other A2UI renderer which depends on `web_core` and uses its basic catalog implementation is also affected. ### Remediation The issue was fixed in [https://github.com/a2ui-project/a2ui/pull/1707](https://github.com/a2ui-project/a2ui/pull/1707) and released in web\_core version 0.10.2, by blocking URLs that do not use the HTTP or HTTPS schemes, or those that are invalid. Please fix this issue in your project by depending on a @a2ui/web\_core version equal or greater than 0.10.2.

Source published

2 Oct 2026 22:55:49 UTC

Source modified

2 Oct 2026 23:15:06 UTC

Saved 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

Source: osv · GitHub Advisory Database · CC-BY-4.0. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

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

Publisher rating · CRITICAL

## Duplicate Advisory This advisory has been withdrawn because it is a duplicate of GHSA-72qq-p3r5-f7wq. This link is maintained to preserve external references. ## Original Description The openUrl function in @a2ui/web_core passes an agent-controlled URL directly to window.open() without validating the URI scheme. A malicious agent can supply a javascript: URI as the url argument of a Button component's functionCall action. When the user clicks the rendered button, arbitrary JavaScript executes in the victim application's browser origin, constituting a stored/reflected XSS with Critical severity. No non-default configuration is required; the Basic Catalog is enabled by default.

Source published

4 Aug 2026 18:31:26 UTC

Source modified

2 Oct 2026 23:00:16 UTC

Saved 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

Source: osv · GitHub Advisory Database · CC-BY-4.0. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

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

CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N/E:U/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Publisher rating · MODERATE