CVE-2025-31277: Apple Safari Buffer Overflow Vulnerability

CVE-2025-31277 Overview

CVE-2025-31277 is a memory corruption vulnerability affecting Apple's WebKit-based browser engine across Safari and multiple Apple operating systems. Processing maliciously crafted web content can trigger memory corruption, allowing attackers to compromise the targeted device. The flaw is classified under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer).

Apple addressed the issue with improved memory handling in Safari 18.6, iOS 18.6, iPadOS 18.6, macOS Sequoia 15.6, tvOS 18.6, visionOS 2.6, and watchOS 11.6. CISA added this CVE to the Known Exploited Vulnerabilities (KEV) catalog, confirming active exploitation in the wild.

Critical Impact

A remote attacker can achieve memory corruption through web content, enabling potential arbitrary code execution on unpatched Apple devices.

Affected Products

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

Discovery Timeline

• 2025-07-30 - CVE-2025-31277 published to NVD
• 2026-04-03 - Last updated in NVD database

Technical Details for CVE-2025-31277

Vulnerability Analysis

The vulnerability resides in WebKit, the browser engine used by Safari and all third-party browsers on iOS and iPadOS. When WebKit parses specifically crafted web content, the rendering pipeline mishandles memory operations, leading to corruption of process memory.

Memory corruption flaws in browser engines frequently serve as the initial foothold in exploit chains. Successful exploitation can enable arbitrary code execution within the renderer process, which attackers then chain with sandbox escapes for full device compromise. Google Cloud Threat Intelligence linked this CVE to the DarkSword iOS exploit chain.

Root Cause

The root cause is improper memory handling within WebKit when processing untrusted web content. Apple's advisory states the fix involved "improved memory handling," indicating the original code path failed to enforce correct bounds or lifetime guarantees on memory buffers manipulated during content rendering.

Attack Vector

Exploitation requires a victim to visit a malicious web page or load attacker-controlled content in any WebKit-based application. User interaction is required, but the bar is low — visiting a link, opening an HTML email, or loading content in an in-app browser is sufficient. The attack is fully remote and requires no privileges.

Given the inclusion in the CISA KEV catalog and reporting of an iOS exploit chain involving this CVE, the vulnerability has been weaponized against real-world targets.

Detection Methods for CVE-2025-31277

Indicators of Compromise

• Unexpected Safari or WebKit-based application crashes referencing memory access violations in renderer processes
• Outbound network connections from mobile devices to infrastructure documented in the DarkSword iOS exploit chain reporting
• Anomalous browser process behavior such as spawning child processes or accessing files outside the sandbox

Detection Strategies

• Monitor endpoint telemetry for Safari and WebKit (com.apple.WebKit.WebContent) process crashes correlated with web browsing activity
• Inspect web proxy and DNS logs for connections to known exploit-delivery domains and JavaScript payloads targeting WebKit
• Track installed OS and Safari versions across the fleet to identify devices still vulnerable

Monitoring Recommendations

• Apply CISA KEV-driven detection content prioritizing Apple ecosystem vulnerabilities under active exploitation
• Forward macOS endpoint logs and crash reports to a centralized SIEM for correlation with threat intelligence feeds
• Alert on lateral movement or privilege escalation following any suspected browser-based compromise

How to Mitigate CVE-2025-31277

Immediate Actions Required

• Update all Apple devices to Safari 18.6, iOS 18.6, iPadOS 18.6, macOS Sequoia 15.6, tvOS 18.6, visionOS 2.6, or watchOS 11.6
• Prioritize patching for mobile devices and executives, given confirmed exploitation in the wild
• Audit mobile device management (MDM) compliance to enforce minimum OS versions

Patch Information

Apple released fixes across its ecosystem on the advisories below:

• Apple Security Advisory #124147
• Apple Security Advisory #124149
• Apple Security Advisory #124152
• Apple Security Advisory #124153
• Apple Security Advisory #124154
• Apple Security Advisory #124155

Workarounds

• Enable Lockdown Mode on iOS, iPadOS, and macOS for high-risk users to restrict WebKit attack surface
• Restrict browsing to trusted sites and block known malicious domains at the network gateway until patching completes
• Disable JavaScript in Safari for unmanaged or legacy devices that cannot be updated promptly

# Verify patched macOS and Safari versions
sw_vers -productVersion   # Expect 15.6 or later for macOS Sequoia
defaults read /Applications/Safari.app/Contents/Info.plist CFBundleShortVersionString   # Expect 18.6 or later