Summary
ckan-mcp-server: DataStore Table UI resource does not validate postMessage origin (in) and posts to targetOrigin "*" (out)
The MCP Apps UI resource (an interactive DataStore table rendered in the host's webview/iframe) communicates with its parent via postMessage. Its inbound message listener performs no event.origin validation, and its outbound messages are sent with target origin '*'. Any window/frame able to reach the document can inject data into the table and interfere with the MCP UI handshake, and the UI's own JSON-RPC messages are broadcast without an origin restriction.
Affected code
src/resources/datastore-table-ui.ts (inline HTML):
window.addEventListener('message', function (event) {
var msg = event.data; // no check of event.origin
if (!msg || typeof msg !== 'object') return;
if (msg.id !== undefined && _pending[msg.id]) { ... resolve/reject pending MCP request ... }
...
if (data && (data.fields || data.records)) initTable(data); // renders attacker-supplied data
});
// outbound:
window.parent.postMessage({ jsonrpc: '2.0', id: id, method: method, params: params || {} }, '*');
mcpNot: window.parent.postMessage({ jsonrpc:'2.0', method:method, params:params||{} }, '*');
There is no allowlist of accepted origins for inbound messages and no fixed target origin for outbound messages.
Proof of concept
poc/verify-no-origin-check.mjs, static confirmation that the listener has no
origin check and outbound uses'*':[x] validates event.origin : NO [x] outgoing postMessage targetOrigin : '*' (any) RESULT: VULNERABLEpoc/parent-spoof-poc.html, a page that embeds the UI and injects fabricated
rows cross-origin with no handshake; the UI renders them.
Impact
- Content spoofing. A frame that can
postMessageto the UI can supply
arbitraryfields/records, causing the table to render fabricated rows and
links (e.g. a phishing__link_url) that appear to come from the queried
portal. (Values are HTML-escaped, so this is display spoofing, not script
injection, no XSS.) - Handshake/UX interference. Because inbound messages matching a pending
id
resolve/reject the UI's MCP requests, an attacker frame can spoof responses to
theui/initializehandshake or otherwise disrupt the panel. - Outbound leakage. Posting to
'*'means the UI's JSON-RPC messages are
delivered to whatever the parent origin is; if the resource is ever embedded by
a context other than the trusted host, those messages leak to it.
Exploitability depends on the host embedding model (in a correct MCP Apps host the
parent is the trusted host, which limits who can message the frame), so this is a
hardening / defense-in-depth issue rather than a directly remotely-triggerable
one, hence Low.
CVE-2026-76894 has a CVSS score of 3.1 (Low). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.4.112); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
- Validate
event.originagainst the expected host origin on every inbound
message; drop messages from other origins. - Send outbound
postMessagewith an explicit target origin (the host origin
established at initialize time) instead of'*'. - Optionally, bind to a nonce/channel established during
ui/initializeso only
the negotiated host can drive the panel.
Frequently Asked Questions
- What is CVE-2026-76894? CVE-2026-76894 is a low-severity security vulnerability in @aborruso/ckan-mcp-server (npm), affecting versions < 0.4.112. It is fixed in 0.4.112.
- How severe is CVE-2026-76894? CVE-2026-76894 has a CVSS score of 3.1 (Low). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of @aborruso/ckan-mcp-server are affected by CVE-2026-76894? @aborruso/ckan-mcp-server (npm) versions < 0.4.112 is affected.
- Is there a fix for CVE-2026-76894? Yes. CVE-2026-76894 is fixed in 0.4.112. Upgrade to this version or later.
- Is CVE-2026-76894 exploitable, and should I be worried? Whether CVE-2026-76894 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-76894 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-76894? Upgrade
@aborruso/ckan-mcp-serverto 0.4.112 or later.