# CVE-2026-40451: Cross-site scripting in Chrome browser extension

> An attacker can execute arbitrary scripts and inject malicious HTML into web pages viewed by users of the DeepL Chrome extension.

- **Severity:** Medium 5.1 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/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:** 22 Apr 2026
- **Updated:** 22 Apr 2026

## What is CVE-2026-40451?

CVE-2026-40451 is a medium-severity cross-site scripting vulnerability in DeepL Chrome browser extension, published on 22 Apr 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

DeepL Chrome browser extension versions from v1.22.0 to v.1.23.0 contain a cross-site scripting vulnerability, which allows an attacker to execute arbitrary script in a user's browser, and inject malicious HTML into web pages viewed by the user.

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

## Which versions are affected by CVE-2026-40451?


## How do I fix CVE-2026-40451?

No fix has been published for CVE-2026-40451 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-40451 being exploited?

There is no known exploitation of CVE-2026-40451 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-40451 and fix it if it is affected.

What it is: CVE-2026-40451 is a medium-severity cross-site scripting vulnerability in DeepL Chrome browser extension, published on 22 Apr 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-2026-40451 in the wild and no public exploit code.

Affected product: DeepL Chrome browser extension. 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-2026-40451/ (Markdown: https://insights.sbomify.com/CVE-2026-40451/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-40451
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40451
- OSV: https://osv.dev/vulnerability/CVE-2026-40451

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-40451/
Summaries are generated and may contain mistakes; the official description above is the record.