Repeated external URL scheme launches could potentially cause a denial of service in Firefox for iOS

published 2026-09-08 2 mo ago modified 2026-10-05 35 d ago also EUVD-2026-72875

cvss: 4.3; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.3%; EPSS 0.3% chance of exploitation in 30 days, percentile 20%
public exploits: 0; none known

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.

Patch / fix

fixed in 1

mozilla firefox 155.1

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 2 mo ago (2026-09-08)

Exploit prediction

0.28% chance of exploitation in the next 30 days, higher than 20% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CISA ADP	3.1	4.3	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L
CNA	3.1	4.3	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L

Affected products

Mozilla Firefox for iOS

Classification

Weakness

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

References

mozilla.org /security/advisories/mfsa2026-89/
vendor-advisory
bugzilla.mozilla.org /show_bug.cgi?id=1847631
permissions-required

Sources

CVE List CVE-2026-86853
NVD CVE-2026-86853

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.

Summary