CVE-2025-43211: Apple Safari Denial of Service Vulnerability

CVE-2025-43211 Overview

CVE-2025-43211 is a denial-of-service vulnerability affecting Apple's WebKit-based Safari browser and multiple Apple operating systems. Processing malicious web content can trigger a resource-handling flaw that leads to service disruption on the affected device. Apple addressed the issue through improved memory handling in Safari 18.6, iOS 18.6, iPadOS 18.6, iPadOS 17.7.9, macOS Sequoia 15.6, tvOS 18.6, visionOS 2.6, and watchOS 11.6. The vulnerability is categorized under [CWE-770] Allocation of Resources Without Limits or Throttling.

Critical Impact
An attacker who convinces a user to process crafted web content can cause the browser or system component to become unresponsive, disrupting availability on the local device.

Affected Products

Apple Safari (versions prior to 18.6)
Apple iOS and iPadOS (versions prior to 18.6, and iPadOS prior to 17.7.9)
Apple macOS Sequoia (versions prior to 15.6), tvOS (prior to 18.6), visionOS (prior to 2.6), and watchOS (prior to 11.6)

Discovery Timeline

2025-07-30 - CVE-2025-43211 published to the National Vulnerability Database (NVD)
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-43211

Vulnerability Analysis

The vulnerability resides in Apple's web content processing pipeline, which is used across Safari and Apple operating systems that render HTML, JavaScript, and CSS. When the affected component processes specially crafted web content, insufficient memory handling causes uncontrolled resource consumption. The result is a denial-of-service condition impacting the availability of the browser or operating system component.

Apple's advisory attributes the fix to improved memory handling. The weakness maps to [CWE-770], Allocation of Resources Without Limits or Throttling. This class of flaw occurs when software allocates memory or other resources based on attacker-controlled inputs without enforcing appropriate bounds.

Root Cause

The root cause is a lack of adequate constraints on memory allocations during web content processing. Malformed or adversarial inputs cause allocations that exhaust available resources, driving the affected process into an unrecoverable state. Apple's remediation adds tighter checks and improved allocation handling to prevent the runaway condition.

Attack Vector

Exploitation requires the victim to load attacker-controlled web content in a vulnerable Apple product. The attack vector is local to the device processing the content, and no authentication or user privileges are required beyond browsing the page. Successful exploitation impacts availability only; there is no reported confidentiality or integrity impact.

No public proof-of-concept exploit is available at this time, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog.

Detection Methods for CVE-2025-43211

Indicators of Compromise

Repeated Safari or WebKit process crashes and unexpected termination events on Apple endpoints after visiting specific web pages.
Sudden spikes in memory consumption tied to the Safari, WebContent, or com.apple.WebKit processes.
CrashReporter entries referencing WebKit rendering components following browsing sessions on untrusted domains.

Detection Strategies

Inventory managed Apple endpoints and confirm operating system and Safari versions against the fixed builds listed in Apple advisories 124147 through 124155.
Correlate browser crash telemetry with proxy or DNS logs to identify domains that consistently trigger WebKit process termination.
Alert on abnormal memory growth patterns in browser child processes on macOS, iOS, and iPadOS fleets.

Monitoring Recommendations

Collect and centralize macOS ReportCrash and unified log data referencing WebKit and Safari processes.
Monitor MDM compliance reports for devices lagging behind the fixed operating system versions.
Track outbound web traffic to newly observed or low-reputation domains delivered via email, messaging, or ad networks.

How to Mitigate CVE-2025-43211

Immediate Actions Required

Upgrade Safari to version 18.6 and update Apple operating systems to iOS 18.6, iPadOS 18.6 or 17.7.9, macOS Sequoia 15.6, tvOS 18.6, visionOS 2.6, and watchOS 11.6.
Push updates through mobile device management (MDM) tooling and enforce compliance policies for devices that do not update within the defined window.
Warn users against opening untrusted links from email, messaging apps, and ad networks until patching is complete.

Patch Information

Apple published fixes across product families in the following advisories: Apple Support Document 124147, 124148, 124149, 124152, 124153, 124154, and 124155. Debian users can reference the Debian LTS Announcement August 2025 for related WebKit updates. Additional community discussion is available on the Full Disclosure August 2025 post and the OWASP Security August 2025 post.

Workarounds

Restrict access to untrusted or unnecessary websites through web filtering, DNS security, or secure web gateway policies until updates are deployed.
Use alternate browsers on macOS for high-risk browsing scenarios where Safari cannot be updated immediately.
Disable JavaScript execution for untrusted origins in enterprise-managed Safari profiles as a temporary risk-reduction measure.

bash

# Verify current Safari version on macOS endpoints
defaults read /Applications/Safari.app/Contents/Info.plist CFBundleShortVersionString

# Trigger a software update check on macOS
sudo softwareupdate --list
sudo softwareupdate --install --all --restart