CVE-2025-31266 Overview
CVE-2025-31266 is a spoofing vulnerability in Apple Safari and macOS Sequoia. The flaw stems from improper truncation of the fully qualified domain name (FQDN) when Safari renders the title of a pop-up window. A malicious website can craft a domain that visually deceives users into trusting attacker-controlled origins.
Apple addressed the issue in Safari 18.5 and macOS Sequoia 15.5 by improving truncation logic. The vulnerability is tracked as [CWE-451: User Interface (UI) Misrepresentation of Critical Information].
Critical Impact
Attackers can spoof trusted domain names in Safari pop-up window titles, enabling convincing phishing and credential-harvesting campaigns against macOS users.
Affected Products
- Apple Safari versions prior to 18.5
- Apple macOS Sequoia versions prior to 15.5
- Web applications and users relying on Safari domain display for trust decisions
Discovery Timeline
- 2025-11-21 - CVE-2025-31266 published to the National Vulnerability Database (NVD)
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-31266
Vulnerability Analysis
The vulnerability resides in how Safari displays the FQDN in the title bar of pop-up windows. When a domain name exceeds the visible width of the title area, Safari truncates the string in a way that lets attackers hide the true origin. A crafted subdomain can push a legitimate-looking string into the visible portion while the actual controlling domain is hidden by truncation.
Exploitation requires user interaction, since the victim must visit a malicious page and interact with the resulting pop-up. No authentication or elevated privileges are needed on the target system. The flaw does not permit code execution or data theft directly, but it undermines the origin indicators that users rely on for trust decisions.
Root Cause
The root cause is a UI misrepresentation issue [CWE-451]. Safari's title rendering logic did not correctly truncate long FQDNs to preserve the security-relevant portion of the domain. Apple's fix implements improved truncation that ensures the effective second-level domain remains visible.
Attack Vector
The attack begins when a user visits an attacker-controlled site over the network. The site opens a pop-up window with a crafted long hostname such as trusted-bank.example.com.attacker-controlled-domain.tld. Safari's truncation causes the visible portion of the title to appear as a trusted domain, while the actual origin remains attacker-controlled. Adversaries typically pair this technique with phishing pages that request credentials, session tokens, or multi-factor codes.
No verified public exploit or proof-of-concept has been published for CVE-2025-31266. Refer to the Apple Support Article #122716 and Apple Support Article #122719 for vendor technical details.
Detection Methods for CVE-2025-31266
Indicators of Compromise
- Pop-up windows opened from unfamiliar parent pages that request credentials or session data
- Outbound HTTP/HTTPS connections to newly registered domains with long, deceptive subdomain chains
- Safari user-agent traffic to domains where the leftmost labels mimic well-known brands
- User reports of login prompts appearing in windows spawned by unrelated web pages
Detection Strategies
- Inventory macOS endpoints and identify hosts running Safari versions earlier than 18.5 or macOS Sequoia earlier than 15.5
- Correlate web proxy or DNS telemetry to flag domains whose left-side labels contain trusted brand names embedded within untrusted parent domains
- Monitor phishing-report queues and email gateways for lures directing macOS users to pop-up-based credential pages
Monitoring Recommendations
- Ingest Safari browsing telemetry and DNS resolution logs into a centralized analytics platform for retrospective hunting
- Alert on authentication events originating shortly after visits to newly observed domains with high label counts
- Track patch compliance status for Safari and macOS Sequoia across managed fleets
How to Mitigate CVE-2025-31266
Immediate Actions Required
- Update Safari to version 18.5 or later on all managed macOS devices
- Update macOS Sequoia to version 15.5 or later to receive the bundled Safari fix
- Communicate phishing awareness guidance to users, emphasizing that pop-up titles may misrepresent domains on unpatched systems
- Enforce update compliance through mobile device management (MDM) policies
Patch Information
Apple released fixes for CVE-2025-31266 in Safari 18.5 and macOS Sequoia 15.5. Full advisory details are available in Apple Support Article #122716 and Apple Support Article #122719. The patch improves FQDN truncation logic so the security-relevant portion of the domain remains visible in pop-up titles.
Workarounds
- Configure Safari to block pop-up windows by default via Settings → Websites → Pop-up Windows
- Deploy enterprise phishing protection and DNS filtering to block newly registered or lookalike domains
- Require phishing-resistant authentication such as WebAuthn or hardware security keys to reduce credential-theft impact
- Restrict administrative access on macOS endpoints until patches are fully deployed
# Verify Safari and macOS versions on a managed endpoint
sw_vers -productVersion
defaults read /Applications/Safari.app/Contents/Info.plist CFBundleShortVersionString
# Enforce pop-up blocking via MDM configuration profile key
# com.apple.Safari : WebKitJavaScriptCanOpenWindowsAutomatically = false
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
