# CVE-2026-86853: Repeated external URL scheme launches could potentially cause a denial of service in Firefox for iOS

> A malicious webpage can cause a denial of service in Firefox for iOS by repeatedly triggering external URL schemes, requiring an upgrade to fix.

- **Severity:** Medium 4.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L`)
- **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:** 8 Sep 2026
- **Updated:** 8 Sep 2026
- **Also known as:** GHSA-4c3m-8r8c-3rf3

## What is CVE-2026-86853?

CVE-2026-86853 is a medium-severity denial of service vulnerability in Mozilla Firefox Mobile, published on 8 Sep 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

A malicious webpage could repeatedly trigger external URL schemes, causing system prompts or external application launches. This could make Firefox for iOS temporarily unusable until the page is closed. This vulnerability was fixed in Firefox for iOS 155.1.

Weakness: CWE-451 (User Interface (UI) Misrepresentation of Critical Information)

## Which versions are affected by CVE-2026-86853?

It affects 1 product.


Products: Mozilla Firefox Mobile.

## How do I fix CVE-2026-86853?

No fix has been published for CVE-2026-86853 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-86853 being exploited?

There is no known exploitation of CVE-2026-86853 in the wild and no public exploit code.

## Other vulnerabilities in Mozilla Firefox Mobile

- [CVE-2026-84135](https://insights.sbomify.com/CVE-2026-84135/): Other issue in Firefox Focus for Android (critical 9.8)
- [CVE-2024-43111](https://insights.sbomify.com/CVE-2024-43111/): Cross-site scripting in Firefox for iOS (critical 9.8)
- [CVE-2023-49060](https://insights.sbomify.com/CVE-2023-49060/): Information disclosure in Firefox for iOS (critical 9.8)
- [CVE-2026-92033](https://insights.sbomify.com/CVE-2026-92033/): Privilege escalation in Firefox for Android (high 8.8)
- [CVE-2026-84117](https://insights.sbomify.com/CVE-2026-84117/): Privilege escalation in Firefox for Android (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-86853 and fix it if it is affected.

What it is: CVE-2026-86853 is a medium-severity denial of service vulnerability in Mozilla Firefox Mobile, published on 8 Sep 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-2026-86853 in the wild and no public exploit code.

Affected product: Mozilla Firefox Mobile. 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-2026-86853/ (Markdown: https://insights.sbomify.com/CVE-2026-86853/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-86853
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-86853
- OSV: https://osv.dev/vulnerability/CVE-2026-86853

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-86853/
Summaries are generated and may contain mistakes; the official description above is the record.