CVE-2026-84549 Overview
CVE-2026-84549 is an out-of-bounds read vulnerability [CWE-125] in the Network File System (NFS) client component of Apple macOS. The flaw allows a malicious NFS server to trigger unexpected system termination or corrupt kernel memory when a client connects to it. Apple addressed the issue with improved bounds checking in macOS Golden Gate 27, macOS Sequoia 15.8, and macOS Tahoe 26.7. The vulnerability is exploitable over the network without authentication or user interaction, and primarily impacts system availability.
Critical Impact
A malicious NFS server can crash affected macOS clients or corrupt kernel memory simply by responding to a mount or file operation request.
Affected Products
- Apple macOS versions prior to Golden Gate 27
- Apple macOS versions prior to Sequoia 15.8
- Apple macOS versions prior to Tahoe 26.7
Discovery Timeline
- 2026-09-14 - CVE-2026-84549 published to NVD
- 2026-09-16 - Last updated in NVD database
Technical Details for CVE-2026-84549
Vulnerability Analysis
The vulnerability resides in the macOS NFS client implementation, which parses responses returned from a remote NFS server. The client fails to correctly validate the length or offset of certain fields in server responses before accessing the underlying memory buffer. When the NFS client reads past the intended buffer boundary, the kernel dereferences memory that lies outside the allocated region.
Because the flawed parsing occurs in kernel context, the resulting out-of-bounds read can leak sensitive kernel memory into subsequent processing or trigger a kernel panic. The Apple advisories describe the outcome as either unexpected system termination or corruption of kernel memory. The confidentiality impact is not scored as high, but the availability impact is severe because a single malicious response can crash the host.
Root Cause
The root cause is missing bounds checking on data supplied by an untrusted NFS server. The client trusts server-provided length fields when indexing into an internal buffer, which allows crafted responses to force reads beyond allocated memory. Apple's fix introduces improved bounds checking on those fields before the read operation is performed.
Attack Vector
Exploitation requires a macOS system to initiate an NFS connection to an attacker-controlled server. This can occur when a user manually mounts a malicious share, when an administrator configures an automount pointing to a compromised host, or when a user is redirected through DNS or network manipulation to a rogue NFS endpoint on a shared network. No authentication and no user interaction beyond the initial connection are required.
No verified proof-of-concept code has been published. The vulnerability mechanism is described in prose only; refer to the Apple Support Document #149035, Apple Support Document #149042, and Apple Support Document #149043 for the official technical description.
Detection Methods for CVE-2026-84549
Indicators of Compromise
- Unexpected kernel panics on macOS endpoints shortly after mounting or browsing an NFS share.
- Outbound TCP or UDP traffic to port 2049 (nfsd) targeting unknown or untrusted hosts.
- mount_nfs process activity referencing NFS servers outside the approved corporate storage inventory.
- Repeated crash reports in /Library/Logs/DiagnosticReports/ referencing the NFS kernel extension.
Detection Strategies
- Inventory macOS endpoints by build number and flag hosts running versions earlier than macOS Sequoia 15.8, macOS Tahoe 26.7, or macOS Golden Gate 27.
- Correlate NFS mount events with destination reputation data to identify connections to unmanaged servers.
- Monitor kernel panic telemetry for signatures matching the NFS client stack.
Monitoring Recommendations
- Enable network flow logging for port 2049 across all corporate subnets and VPN egress points.
- Alert on new NFS mount targets that do not appear in an approved storage allowlist.
- Forward macOS unified logs and crash reports to a centralized platform for correlation with network events.
How to Mitigate CVE-2026-84549
Immediate Actions Required
- Upgrade affected endpoints to macOS Golden Gate 27, macOS Sequoia 15.8, or macOS Tahoe 26.7 as applicable to each hardware generation.
- Restrict outbound NFS traffic (TCP/UDP port 2049) at the network perimeter to a known list of trusted file servers.
- Audit autofs and /etc/fstab configurations to remove entries pointing to untrusted or externally reachable NFS servers.
- Instruct users not to mount NFS shares from untrusted networks or unknown hosts.
Patch Information
Apple released fixes in macOS Golden Gate 27, macOS Sequoia 15.8, and macOS Tahoe 26.7. Patch details and download links are available in Apple Support Document #149035, Apple Support Document #149042, and Apple Support Document #149043. Install updates through System Settings → General → Software Update, or via managed deployment through your mobile device management (MDM) platform.
Workarounds
- Disable NFS client functionality on hosts that do not require it by unloading the NFS kernel extension and removing automount configurations.
- Enforce firewall rules that block outbound connections to port 2049 except toward approved storage subnets.
- Require NFS access to traverse authenticated VPN tunnels that terminate on managed, trusted infrastructure.
# Verify installed macOS build and disable unused NFS automounts
sw_vers -productVersion
sudo automount -vc
sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.autofsd.plist
# Block outbound NFS at the host level using pf
echo "block out proto { tcp udp } to any port 2049" | sudo pfctl -ef -
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
