# CVE-2026-78209: exceljs through 4.4.0 CSV Formula Injection via Unescaped Cell Values

> Attackers can inject malicious formulas into CSV exports via unescaped cell values, leading to data exfiltration or code execution when opened in spreadsheet apps.

- **Severity:** High 8.4 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:L/VA:N/SC:H/SI:L/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 24 Aug 2026
- **Updated:** 29 Aug 2026
- **Also known as:** GHSA-4w2g-jrqm-g99q, GHSA-9wxc-4rhw-hfrw

## What is CVE-2026-78209?

CVE-2026-78209 is a high-severity vulnerability in exceljs, published on 24 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

exceljs through 4.4.0 fails to neutralize leading equals, plus, minus, or at signs in cell values written to CSV output. Attackers who can influence exported cell values can inject formulas that execute when the CSV file is opened in a spreadsheet application, potentially exfiltrating data or performing other malicious actions.

Weakness: CWE-1236 (Improper Neutralization of Formula Elements in a CSV File)

## Which versions are affected by CVE-2026-78209?


## How do I fix CVE-2026-78209?

No fix has been published for CVE-2026-78209 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-78209 being exploited?

There is no known exploitation of CVE-2026-78209 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-78209 and fix it if it is affected.

What it is: CVE-2026-78209 is a high-severity vulnerability in exceljs, published on 24 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-78209 in the wild and no public exploit code.

Affected product: exceljs. 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-2026-78209/ (Markdown: https://insights.sbomify.com/CVE-2026-78209/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-78209
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-78209
- OSV: https://osv.dev/vulnerability/CVE-2026-78209

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-78209/
Summaries are generated and may contain mistakes; the official description above is the record.