CVE-2026-28835: Apple macOS Use-After-Free Vulnerability

CVE-2026-28835 Overview

CVE-2026-28835 is a use-after-free vulnerability in Apple macOS that affects the SMB (Server Message Block) network file sharing implementation. The vulnerability occurs when mounting a maliciously crafted SMB network share, which can trigger improper memory management and lead to system termination. This denial-of-service condition could disrupt enterprise workflows and potentially be leveraged in targeted attacks against macOS endpoints in corporate environments.

Critical Impact

Mounting a maliciously crafted SMB network share may lead to system termination, causing denial of service on affected macOS systems.

Affected Products

• macOS Sequoia versions prior to 15.7.5
• macOS Sonoma versions prior to 14.8.5
• macOS Tahoe versions prior to 26.4

Discovery Timeline

• 2026-03-25 - CVE-2026-28835 published to NVD
• 2026-03-25 - Last updated in NVD database

Technical Details for CVE-2026-28835

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a memory corruption vulnerability class that occurs when a program continues to reference memory after it has been freed. In the context of CVE-2026-28835, the macOS SMB client contains a flaw in its memory management routines that can be exploited when processing specially crafted SMB network shares.

Use-after-free vulnerabilities occur when dynamically allocated memory is freed but pointers to that memory are not properly invalidated. Subsequent operations that reference this freed memory can result in undefined behavior, including crashes, data corruption, or in some cases, code execution. For CVE-2026-28835, exploitation results in system termination, indicating the kernel or a critical system process is affected.

Root Cause

The root cause of CVE-2026-28835 lies in improper memory management within the macOS SMB client implementation. When processing certain malformed or specially crafted SMB responses, the system fails to properly track the lifecycle of memory objects. This leads to a condition where freed memory is subsequently accessed, triggering the use-after-free condition.

Apple addressed this issue by implementing improved memory management to ensure proper tracking and validation of memory objects throughout their lifecycle in SMB operations.

Attack Vector

The attack vector for CVE-2026-28835 is network-based and requires user interaction. An attacker would need to:

1. Set up a malicious SMB server configured to send specially crafted responses
2. Entice or trick a user into mounting the malicious SMB network share
3. When the victim mounts the share, the malformed data triggers the use-after-free condition
4. The system terminates, resulting in denial of service

This attack could be delivered through phishing emails containing links to malicious SMB shares, compromised internal file servers, or man-in-the-middle attacks on legitimate SMB traffic. Enterprise environments with extensive SMB usage for file sharing are particularly at risk.

Detection Methods for CVE-2026-28835

Indicators of Compromise

• Unexpected system crashes or kernel panics when connecting to SMB shares
• Unusual SMB connection attempts to unfamiliar or suspicious network locations
• System logs showing SMB-related memory allocation errors or crashes
• Reports of multiple endpoints experiencing crashes after accessing the same network share

Detection Strategies

• Monitor for repeated system terminations correlated with SMB mount operations
• Implement network monitoring to detect connections to unauthorized or suspicious SMB servers
• Review system crash reports for signatures indicating use-after-free conditions in SMB components
• Deploy endpoint detection rules to alert on abnormal SMB client behavior patterns

Monitoring Recommendations

• Enable verbose logging for SMB client operations on critical systems
• Configure network security tools to inspect SMB traffic for malformed packets
• Set up alerts for multiple system crashes across endpoints within a short timeframe
• Monitor for connections to SMB shares outside of known-good internal file servers

How to Mitigate CVE-2026-28835

Immediate Actions Required

• Update to macOS Sequoia 15.7.5, macOS Sonoma 14.8.5, or macOS Tahoe 26.4 immediately
• Restrict SMB connections to trusted internal file servers only
• Warn users not to mount SMB shares from untrusted or unknown sources
• Review firewall rules to limit outbound SMB traffic to approved destinations

Patch Information

Apple has released security updates that address CVE-2026-28835 with improved memory management:

• macOS Sequoia 15.7.5 - Apple Security Advisory #126794
• macOS Sonoma 14.8.5 - Apple Security Advisory #126795
• macOS Tahoe 26.4 - Apple Security Advisory #126796

Organizations should prioritize deployment of these updates through their endpoint management solutions.

Workarounds

• Block outbound SMB traffic (TCP ports 139 and 445) at the network perimeter to prevent connections to external malicious servers
• Use application firewall rules to restrict SMB client connections to a whitelist of trusted servers
• Disable automatic mounting of network shares in environments where SMB is not business-critical
• Implement network segmentation to isolate systems that must connect to untrusted SMB resources

# Block outbound SMB traffic at the macOS firewall level
# Add these rules to restrict SMB connections to trusted servers only
sudo /usr/libexec/ApplicationFirewall/socketfilterfw --setblockall on
# Whitelist specific trusted SMB servers in your organization's firewall
# Consult Apple documentation for proper pfctl configuration