WhatsApp Issues Emergency Patch for CVE-2025-55177 Affecting iOS and macOS Linked‑Device Sync

What happened

WhatsApp issued an emergency update for its iOS and macOS clients to remediate a high‑severity vulnerability the company said may have been used in targeted zero‑day attacks. According to WhatsApp, the bug — tracked as CVE‑2025‑55177 and assigned a CVSS score of 8.0 — involves insufficient authorization of linked‑device synchronization messages and could be leveraged in conjunction with a recently disclosed Apple flaw.

The vulnerability, CVE-2025-55177 (CVSS score: 8.0), relates to a case of insufficient authorization of linked device synchronization messages.

WhatsApp’s advisory indicates the issue affects the messaging app implementations on Apple platforms (iOS and macOS). The company released updates and urged users on those platforms to install them immediately.

Technical background and why it matters

WhatsApp’s multi‑device or linked‑device capability allows a primary phone to pair secondary clients (desktop or another mobile device) and synchronize messages so users can access their conversations without the primary device being online. Synchronization requires authentication and message exchange between the primary and linked devices.

“Insufficient authorization of linked device synchronization messages” implies that some synchronization requests or responses were accepted without full verification of the device’s credentials or session state. In practice, such a flaw can let an attacker trick a client into accepting a malicious or unauthorized linked device, or permit an attacker to inject or retrieve message data during the sync process.

The problem is particularly serious because it was reported in combination with a separate Apple vulnerability that had been disclosed recently. When an app‑level flaw — like an authentication bypass in a sync protocol — is chained with an operating‑system vulnerability that permits remote code execution or privilege escalation, attackers can mount zero‑click attacks that require no user interaction to compromise targeted devices.

Comparable incidents and historical context

Zero‑click messaging exploits have been used previously against high‑value targets. Well‑documented campaigns involving commercial surveillance tools have exploited vulnerabilities in popular messaging platforms and mobile operating systems to achieve remote compromise without user interaction. These incidents show a pattern: attackers prefer chains that combine an app‑level weakness (improper authentication, parsing bugs, etc.) with an OS‑level exploit to gain persistence or access to sensitive data.

• Zero‑click attacks are rare relative to commodity malware, but they are a favored technique in targeted espionage because they reduce dependence on user behavior and increase stealth.
• A CVSS score of 8.0 places CVE‑2025‑55177 in the “high” severity range; paired with an OS‑level zero‑day, the combined risk becomes critical for targeted users and organizations holding sensitive information.

Practitioner analysis: what defenders and investigators should consider

For security teams, rapid patch deployment is the immediate priority, but response and detection require a broader set of actions. Key considerations:

• Patch and harden:
  • Deploy the updated WhatsApp client to all managed macOS and iOS endpoints immediately. Use mobile device management (MDM) solutions to enforce updates where possible.
  • Ensure Apple operating systems are also up to date; if Apple has released mitigations for the related flaw, apply those patches promptly.
• Inventory and validate linked devices:
  • Audit the list of linked devices for each account in scope. Remove any unknown or unexpected pairings and require re‑authentication.
  • For high‑risk users (executives, journalists, dissidents), consider temporarily disabling linked‑device functionality until the environment is confirmed clean and patched.
• Detection and logging:
  • Enable and collect relevant logs from endpoints and network appliances. Look for anomalous WhatsApp synchronization traffic, unexpected device registration events, or unusual TLS sessions to WhatsApp infrastructure or third‑party relays.
  • Correlate device network logs with known suspicious activity windows to identify potential exploitation timelines.
• Forensic preservation:
  • If compromise is suspected, preserve device images, application logs, and system diagnostics. On Apple platforms, gather sysdiagnose output and secure backups for further analysis.
  • Do not power‑cycle potentially compromised devices unnecessarily — document chain of custody and work with specialized mobile forensic tools or labs when needed.
• Threat hunting:
  • Hunt for indicators such as unexpected background processes, changes to certificate stores, or new authorized device relationships within WhatsApp clients.
  • Monitor for lateral movement or data exfiltration patterns that could follow a successful message synchronization compromise.

Potential risks, implications and actionable recommendations for users

For individual users and organizations, the most immediate risk is unauthorized access to messages and attachments via a linked device or chained exploit. The long‑term implications include potential data exposure, targeted surveillance of high‑profile accounts, and erosion of trust in the client if exploits are widely publicized.

Actionable steps for users and administrators:

• Update WhatsApp on iOS and macOS immediately to the patched version provided by the vendor.
• Update Apple device operating systems as Apple releases fixes for any related vulnerabilities.
• Review linked devices in WhatsApp settings; unlink any device you do not recognize. Re‑link devices only after updates are installed.
• Enable WhatsApp’s two‑step verification (a PIN) to add a layer of account protection that can limit unauthorized re‑provisioning.
• For sensitive users, consider limiting use of linked‑device features temporarily and prefer single‑device operation until the threat environment stabilizes.
• Follow basic device hygiene: strong passcodes, biometric locks, full‑disk encryption where available, and constrained app permissions.

Conclusion

WhatsApp’s emergency update for CVE‑2025‑55177 addresses a high‑severity weakness in linked‑device synchronization that may have been exploited alongside a separate Apple flaw to execute targeted zero‑click attacks. The combination of an app‑level authorization issue and an OS‑level vulnerability underlines why multi‑stage exploit chains are especially dangerous. Immediate steps are straightforward: apply the patched WhatsApp clients and relevant Apple OS updates, audit linked devices, and follow hardening and detection guidance for endpoints. For defenders, the incident is a reminder to prioritize rapid patching, maintain robust inventory and logging, and prepare for forensic response when targeted attacks are suspected.

Source: thehackernews.com