# CVE-2026-74939: Privilege escalation in the DOM: Navigation component

> Attackers can escalate privileges via the DOM Navigation component in Firefox and Thunderbird, requiring users to upgrade to patched versions.

- **Severity:** High 8.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H`)
- **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:** Yes
- **Published:** 18 Aug 2026
- **Updated:** 21 Aug 2026
- **Also known as:** DEBIAN-CVE-2026-74939, GHSA-mcwh-jxcv-xq9h, UBUNTU-CVE-2026-74939

## What is CVE-2026-74939?

CVE-2026-74939 is a high-severity vulnerability in Mozilla Firefox, published on 18 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

Privilege escalation in the DOM: Navigation component. This vulnerability was fixed in Firefox 154, Firefox ESR 115.39, Firefox ESR 140.14, Firefox ESR 153.1, Thunderbird 154, Thunderbird 140.14, and Thunderbird 153.1.

Weakness: CWE-269 (Improper Privilege Management)

## Which versions are affected by CVE-2026-74939?

It affects 2 products.


Products: Mozilla Firefox, Mozilla Thunderbird.

## How do I fix CVE-2026-74939?

Upgrade to a fixed version.

## Is CVE-2026-74939 being exploited?

There is no known exploitation of CVE-2026-74939 in the wild and no public exploit code.

Public exploit code:

- Firefox content-to-parent IPDL privilege escalation (N-day, bug 2054416): forged PDocumentChannel with RemoteTypeOverride -> privilegedabout process placement, via mojo-port send-path injection from a compromised content process (github_poc): https://github.com/SneakyNachos/CVE-2026-74939-escape-the-mac-n-cheese-box

## Other vulnerabilities in Mozilla Firefox

- [CVE-2019-11708](https://insights.sbomify.com/CVE-2019-11708/): Mozilla Firefox and Thunderbird Sandbox Escape (critical 10.0, exploited in the wild)
- [CVE-2010-3765](https://insights.sbomify.com/CVE-2010-3765/): Mozilla Multiple Products Remote Code Execution (critical 9.8, exploited in the wild)
- [CVE-2022-26486](https://insights.sbomify.com/CVE-2022-26486/): Mozilla Firefox Use-After-Free (critical 9.6, exploited in the wild)
- [CVE-2022-26485](https://insights.sbomify.com/CVE-2022-26485/): Mozilla Firefox Use-After-Free (high 8.8, exploited in the wild)
- [CVE-2019-11707](https://insights.sbomify.com/CVE-2019-11707/): Mozilla Firefox and Thunderbird Type Confusion (high 8.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74939 and fix it if it is affected.

What it is: CVE-2026-74939 is a high-severity vulnerability in Mozilla Firefox, published on 18 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-2026-74939 in the wild and no public exploit code.

Affected product: Mozilla Firefox. 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-2026-74939/ (Markdown: https://insights.sbomify.com/CVE-2026-74939/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74939
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74939
- OSV: https://osv.dev/vulnerability/CVE-2026-74939

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74939/
Summaries are generated and may contain mistakes; the official description above is the record.