CVE-2025-31240 Overview
CVE-2025-31240 is an input validation flaw [CWE-20] in Apple macOS that allows a maliciously crafted Apple Filing Protocol (AFP) network share to terminate the operating system. When a user mounts the malicious share, improper checks in the AFP client cause a system crash, resulting in denial of service.
Apple addressed the issue with improved checks in macOS Sequoia 15.5, macOS Sonoma 14.7.6, and macOS Ventura 13.7.6. The vulnerability is exploitable over the network without authentication or user privileges, but requires a user to initiate the AFP mount operation.
Critical Impact
A remote attacker hosting a crafted AFP share can force a complete system termination on vulnerable macOS endpoints, disrupting availability for any user who mounts the share.
Affected Products
- Apple macOS Ventura (versions prior to 13.7.6)
- Apple macOS Sonoma (versions prior to 14.7.6)
- Apple macOS Sequoia (versions prior to 15.5)
Discovery Timeline
- 2025-05-12 - CVE-2025-31240 published to NVD
- 2025-05-12 - Apple releases security patches in macOS Sequoia 15.5, Sonoma 14.7.6, and Ventura 13.7.6
- 2026-04-02 - Last updated in NVD database
Technical Details for CVE-2025-31240
Vulnerability Analysis
The vulnerability resides in the macOS AFP client code path responsible for processing responses from a remote AFP server during share mounting. According to Apple's advisory, the issue was addressed with improved checks, indicating that input from the server was not adequately validated before use.
When a user mounts an AFP share, the client parses protocol messages and metadata sent by the server. A malformed or malicious response causes the kernel or AFP subsystem to reach an unrecoverable state, terminating the system. The CWE-20 classification confirms the root cause is improper input validation rather than a memory safety bug with code execution potential.
The CVSS vector indicates impact is limited to availability, with no confidentiality or integrity loss. This aligns with system termination behavior rather than arbitrary code execution.
Root Cause
The AFP client does not perform sufficient validation of fields within network responses received from an AFP server. Crafted values trigger a fault condition during share mount processing, causing the operating system to terminate.
Attack Vector
An attacker stands up a malicious AFP server reachable by the target. The attacker then induces the victim to mount the share using afp:// URLs delivered through phishing, malicious documents, web redirects, or shared links. Upon connection, the server returns crafted protocol data that triggers the fault. No credentials are required because the malformed data can be sent during the initial protocol handshake.
The vulnerability cannot be triggered without the user action of mounting the share, but a single click on an afp:// link in many macOS contexts is sufficient to initiate the mount. See the Apple Support advisory for macOS Sequoia 15.5 for vendor details.
Detection Methods for CVE-2025-31240
Indicators of Compromise
- Unexpected kernel panics or system terminations on macOS hosts shortly after AFP mount activity
- Outbound TCP connections to untrusted hosts on port 548 (AFP) from user endpoints
- Presence of afp:// URLs in email, chat, or browser history immediately preceding a crash
- Crash reports referencing AFP client components in /Library/Logs/DiagnosticReports/
Detection Strategies
- Inventory macOS endpoints and flag systems running versions prior to Sequoia 15.5, Sonoma 14.7.6, or Ventura 13.7.6
- Monitor endpoint telemetry for mount_afp process executions targeting external or non-corporate hosts
- Correlate kernel panic events with preceding network connections to TCP port 548
- Inspect proxy and DNS logs for afp:// URL handling and resolution of unexpected file-sharing hosts
Monitoring Recommendations
- Forward macOS unified logs and crash reports to a central SIEM for kernel panic correlation
- Alert on first-time AFP connections from endpoints that have no historical AFP usage
- Track patch compliance for the affected macOS branches across the fleet
How to Mitigate CVE-2025-31240
Immediate Actions Required
- Update macOS endpoints to Sequoia 15.5, Sonoma 14.7.6, or Ventura 13.7.6 as documented in Apple's advisories
- Block outbound TCP port 548 at the network perimeter where AFP is not required
- Educate users to avoid clicking afp:// links from untrusted sources
Patch Information
Apple released fixes on 2025-05-12. Apply the appropriate update based on the macOS branch in use:
Workarounds
- Restrict or disable AFP client functionality on endpoints that do not require legacy file sharing
- Enforce egress filtering to permit AFP (TCP/548) only to known internal file servers
- Use mobile device management policies to prevent users from mounting external afp:// shares
# Block outbound AFP traffic with macOS pf firewall (example)
echo "block out proto tcp to any port 548" | sudo pfctl -ef -
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
