CVE-2025-23109: Firefox iOS Information Disclosure Flaw

CVE-2025-23109 Overview

CVE-2025-23109 is an address bar spoofing vulnerability in Mozilla Firefox for iOS. Attackers can construct URLs with excessively long hostnames to obscure the actual host displayed in the browser address bar. This origin confusion issue [CWE-346] allows adversaries to disguise malicious websites as legitimate ones, enabling phishing and social engineering attacks against users. Mozilla addressed the flaw in Firefox for iOS version 134.

Critical Impact
Attackers can craft URLs that hide the real hostname in the Firefox for iOS address bar, enabling convincing phishing pages that appear to originate from trusted domains.

Affected Products

Mozilla Firefox for iOS versions prior to 134
iOS devices running vulnerable Firefox builds
Users interacting with attacker-controlled URLs delivered via email, messaging, or web content

Discovery Timeline

2025-01-11 - CVE-2025-23109 published to the National Vulnerability Database
2025-01-11 - Mozilla published security advisory MFSA-2025-06
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-23109

Vulnerability Analysis

The vulnerability affects how Firefox for iOS renders long hostnames in the URL bar. When a URL contains an unusually long hostname, the browser truncates or displays the host in a way that hides the true origin. Attackers exploit this rendering behavior to place trusted-looking substrings at the visible portion of the address bar while the real host remains offscreen or elided.

The flaw maps to [CWE-346] Origin Validation Error. The browser correctly resolves the underlying host for network requests, but the UI representation does not accurately convey origin information to the user. This mismatch between the actual origin and the displayed origin is the core defect.

Root Cause

The root cause is insufficient handling of long hostname strings in the address bar UI component of Firefox for iOS. The rendering logic does not enforce a display strategy that preserves the effective top-level domain plus one label (eTLD+1) visibility when hostnames exceed typical lengths.

Attack Vector

Exploitation requires user interaction. An attacker delivers a crafted URL through email, SMS, chat, or a compromised website. When the victim opens the link in Firefox for iOS, the address bar displays a misleading hostname. The victim may then submit credentials or sensitive data believing they are interacting with a trusted site.

No verified proof-of-concept code is publicly available. Technical specifics are tracked in the Mozilla Bug Report #1419275 and the Mozilla Security Advisory MFSA-2025-06.

Detection Methods for CVE-2025-23109

Indicators of Compromise

Outbound HTTP/HTTPS requests to domains containing hostnames longer than 200 characters
Web proxy logs showing URLs with padded or repeated subdomain labels designed to push the real host offscreen
Phishing report submissions referencing pages that appeared to originate from trusted brands but resolved to unrelated hosts

Detection Strategies

Inspect web proxy and DNS telemetry for anomalously long hostnames or FQDNs with excessive label counts
Correlate mobile device browsing telemetry with URL reputation feeds to identify traffic to newly registered or low-reputation domains carrying long hostnames
Deploy phishing-aware email and messaging filters that expand shortened URLs and flag long-hostname patterns before delivery

Monitoring Recommendations

Track Firefox for iOS versions across the mobile fleet through MDM inventory reports
Monitor user-reported phishing incidents involving mobile browsers for patterns consistent with address bar spoofing
Alert on DNS queries where the queried name exceeds a defined length threshold, subject to organizational baselines

How to Mitigate CVE-2025-23109

Immediate Actions Required

Update Firefox for iOS to version 134 or later on all managed and BYOD devices
Push the update through enterprise mobility management (EMM) or mobile device management (MDM) policies
Notify users through security awareness channels to verify hostnames carefully when entering credentials on mobile browsers

Patch Information

Mozilla fixed the vulnerability in Firefox for iOS 134. Refer to the Mozilla Security Advisory MFSA-2025-06 for release details and the Mozilla Bug Report #1419275 for technical tracking.

Workarounds

Use an alternate browser on iOS until the update is applied, or restrict mobile browsing to managed applications with URL inspection
Enable phishing protection features in mobile email and messaging clients to reduce delivery of malicious links
Train users to tap the address bar to reveal the full URL and to verify the effective domain before submitting credentials

bash

# Example MDM command to enforce minimum Firefox for iOS version
# (vendor-specific — consult your MDM documentation)
mdm-cli app-policy set \
  --bundle-id org.mozilla.ios.Firefox \
  --minimum-version 134 \
  --enforcement block-launch