CVE-2025-31277 – High‑Severity Buffer Overflow in Apple WebKit (Safari, iOS, macOS)

Key Takeaways

• CVE-2025-31277 is a High‑severity buffer overflow (CWE‑119) in Apple’s WebKit engine.
• Actively exploited in the wild as part of the DarkSword iOS exploit chain (zero‑click watering‑hole).
• Affected platforms include Safari, iPhone OS, iPadOS, macOS, tvOS, visionOS and watchOS.
• Patch is available in Safari 18.6, iOS 18.6, iPadOS 18.6, macOS Sequoia 15.6, tvOS 18.6, visionOS 2.6, watchOS 11.6.
• Immediate actions: update devices, enable Lockdown Mode, and monitor for malicious web traffic.

Overview

The CVE-2025-31277 vulnerability stems from inadequate memory handling when processing maliciously crafted web content. It triggers a buffer overflow (CWE-119) that can corrupt memory and lead to arbitrary code execution. The flaw is present across the WebKit stack used by Apple’s browsers and web‑view components.

In March 2026, CISA added CVE-2025-31277 to its KEV catalog, flagging it as a known‑exploited vulnerability. Threat‑intelligence reports (Google Threat Intelligence, Aviatrix, etc.) confirm that the vulnerability is being leveraged by the DarkSword iOS exploit chain, which delivers a zero‑click, file‑less attack via malicious Safari pages.

Technical Details

• Vulnerability type: Buffer overflow in WebKit’s JavaScriptCore/rendering pipeline.
• Impact: Memory corruption → remote code execution.
• CVSS 3.1 vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H (Base 8.8 High).
• Exploit chain: DarkSword combines CVE-2025-31277 with additional zero‑days (e.g., CVE-2025-43520) to achieve full device compromise. The chain starts with a malicious web page loaded in Safari; no user click is required, only the page load (UI:R). The exploit loads a custom JavaScript payload that triggers the overflow, gains a read/write primitive, and then executes native code to steal credentials, messages, and cryptocurrency wallets.
• Public leak: A version of the exploit kit was posted on GitHub in early March 2026, lowering the barrier for less‑sophisticated actors.

Severity & Impact

• CVSS Base Score: 8.8 (High)
• Confidentiality: High (complete data exfiltration)
• Integrity: High (tampering with system state)
• Availability: High (potential denial‑of‑service or device bricking)

The combination of a high CVSS score, active exploitation, and a zero‑click delivery makes CVE-2025-31277 one of the most urgent WebKit‑related issues of 2026.

Affected Products

Apple devices running the following components are vulnerable:

• Safari 18.6 (and earlier)
• iPhone OS (iOS) 18.6 (and earlier)
• iPadOS 18.6 (and earlier)
• macOS Sequoia 15.6 (and earlier)
• tvOS 18.6 (and earlier)
• visionOS 2.6 (and earlier)
• watchOS 11.6 (and earlier)

For the complete list of affected versions and CPE identifiers, see the live CVE page: https://vulnsocial.com/cve/CVE-2025-31277.

Actionable Insights – What to Do Now

1. Deploy the patch immediately on all affected devices. Apple released updates for Safari, iOS, iPadOS, macOS, tvOS, visionOS, and watchOS (see References).
2. Enable Lockdown Mode on iPhone OS, iPadOS, and macOS where supported to harden against zero‑click exploits.
3. Validate update compliance across your fleet (MDM, endpoint‑management tools).
4. Block known malicious domains used by the DarkSword watering‑hole (use threat‑intel feeds or DNS filtering).
5. Monitor for Indicators of Compromise (IOCs):
   • Unexpected JavaScript payloads in Safari traffic.
   • Unusual process creation linked to WebKitNetworkProcess.
   • Network connections to suspicious C2 domains reported in recent DarkSword analyses.
6. Apply CISA guidance for cloud services (BOD 22‑01) if your organization relies on Apple‑based SaaS or iOS devices for remote work.
7. Track live threat activity on the VulnSocial CVE page for new exploit sightings or additional mitigation advice: https://vulnsocial.com/cve/CVE-2025-31277.

Remediation & Mitigation

Patch and hardening steps:

1. Update OS and browsers to the versions listed in the Apple security advisories (Safari 18.6, iOS 18.6, etc.).
2. Enable Lockdown Mode (Settings → Privacy & Security → Lockdown Mode).
3. Enforce web‑content filtering to block untrusted JavaScript and known malicious URLs.
4. Deploy endpoint detection that can flag anomalous WebKit activity (e.g., high‑frequency memory allocations, sandbox escapes).
5. Review and restrict remote‑management capabilities; limit privileged access to device configuration.
6. Conduct forensic scans on devices that may have been exposed before the patch, looking for signs of credential or crypto‑wallet theft.

Bottom Line

CVE-2025-31277 is a high‑severity buffer overflow that is actively exploited in the wild via the DarkSword iOS exploit chain. The vulnerability spans the entire Apple WebKit ecosystem and can lead to full device compromise. Immediate patch deployment, enabling Lockdown Mode, and vigilant monitoring are essential to mitigate risk.

References

• Apple Security Advisory – Safari 18.6: https://support.apple.com/en-us/124147
• Apple Security Advisory – iOS 18.6: https://support.apple.com/en-us/124149
• Apple Security Advisory – iPadOS 18.6: https://support.apple.com/en-us/124152
• Apple Security Advisory – macOS Sequoia 15.6: https://support.apple.com/en-us/124153
• Apple Security Advisory – tvOS 18.6: https://support.apple.com/en-us/124154
• Apple Security Advisory – visionOS 2.6 & watchOS 11.6: https://support.apple.com/en-us/124155
• DarkSword technical description (Google Threat Intelligence): https://cloud.google.com/blog/topics/threat-intelligence/darksword-ios-exploit-chain/
• CISA Known Exploited Vulnerabilities Catalog (KEV) entry: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-31277
• Full‑disclosure mailing list archives:
  • http://seclists.org/fulldisclosure/2025/Aug/0
  • http://seclists.org/fulldisclosure/2025/Jul/30
  • http://seclists.org/fulldisclosure/2025/Jul/32
  • http://seclists.org/fulldisclosure/2025/Jul/36

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