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.
- 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
- None listed
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
Which versions are affected by CVE-2026-86853?
It affects 1 product.
Products include 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.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
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
Sources
Also known as GHSA-4c3m-8r8c-3rf3.