# CVE-2026-84942: Stored Cross-Site Scripting via Vega Expression Function Bypass in OpenSearch Dashboards

> Authenticated attackers can execute arbitrary JavaScript in other users' browsers by saving crafted Vega visualizations due to improper input validation.

- **Severity:** Medium 6.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 8 Sep 2026
- **Updated:** 9 Sep 2026
- **Also known as:** GHSA-r4c3-6c67-qqwx

## What is CVE-2026-84942?

CVE-2026-84942 is a medium-severity cross-site scripting vulnerability in AWS Amazon OpenSearch Service, published on 8 Sep 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official description

Improper input validation in the Vega expression function implementation in OpenSearch Dashboards allows a remote authenticated actor with dashboard write permissions to execute arbitrary JavaScript in the context of other users' browser sessions by saving a crafted Vega visualization. The checkForFunctionProperty validation routine failed to recurse into arrays of objects, allowing a function property nested inside an array to bypass validation.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2026-84942?


## How do I fix CVE-2026-84942?

No fix has been published for CVE-2026-84942 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-84942 being exploited?

There is no known exploitation of CVE-2026-84942 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-84942 and fix it if it is affected.

What it is: CVE-2026-84942 is a medium-severity cross-site scripting vulnerability in AWS Amazon OpenSearch Service, published on 8 Sep 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-84942 in the wild and no public exploit code.

Affected product: AWS Amazon OpenSearch Service. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-84942/ (Markdown: https://insights.sbomify.com/CVE-2026-84942/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-84942
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-84942
- OSV: https://osv.dev/vulnerability/CVE-2026-84942

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-84942/
Summaries are generated and may contain mistakes; the official description above is the record.