CVE-2026-43787: Apple macOS Information Disclosure Flaw

CVE-2026-43787 Overview

CVE-2026-43787 is an information disclosure vulnerability in Apple macOS caused by a logic flaw in security check handling. An attacker in a privileged network position can leak sensitive user information by exploiting missing validation in an affected macOS component. Apple addressed the issue with improved checks in macOS Golden Gate 27, macOS Sequoia 15.8, and macOS Tahoe 26.7. The weakness is classified under [CWE-693] Protection Mechanism Failure. The vulnerability requires network adjacency and high attack complexity, which limits opportunistic exploitation but remains relevant for targeted operations against macOS endpoints on untrusted networks.

Critical Impact
A network-adjacent attacker can intercept or observe sensitive user data transmitted or processed by unpatched macOS systems.

Affected Products

Apple macOS Tahoe versions prior to 26.7
Apple macOS Sequoia versions prior to 15.8
Apple macOS Golden Gate versions prior to 27

Discovery Timeline

2026-09-14 - CVE-2026-43787 published to the National Vulnerability Database (NVD)
2026-09-17 - Last updated in NVD database

Technical Details for CVE-2026-43787

Vulnerability Analysis

CVE-2026-43787 is a logic issue in Apple macOS that fails to properly enforce a protection mechanism during network-facing operations. Apple's advisory states the flaw allows an attacker in a privileged network position to leak sensitive user information. The confidentiality impact is high, while integrity and availability are not affected. Successful exploitation does not require user interaction or authentication, but requires high attack complexity, indicating specific conditions must exist on the network path or target configuration.

The issue was resolved with improved checks in the affected component, consistent with a validation gap rather than a memory corruption bug. Apple has not disclosed the affected subsystem in the public advisory beyond the fixed versions.

Root Cause

The root cause is a protection mechanism failure [CWE-693] in which a security check did not correctly evaluate a condition before processing network-derived data. When the condition was not enforced, the affected code path exposed data that should have remained protected. Apple's remediation adds the missing logic to reject or sanitize the untrusted state before sensitive information is emitted.

Attack Vector

Exploitation requires the attacker to occupy a privileged network position between the macOS host and a remote endpoint. Typical positions include a compromised Wi-Fi access point, an on-path router, or a rogue node on a shared broadcast segment. From that position, the attacker manipulates traffic or observes protocol behavior to trigger the flawed code path and extract user information. No credentials or user interaction on the target are needed.

No public proof-of-concept exploit is available, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. See the Apple Security Update Guide for vendor details.

Detection Methods for CVE-2026-43787

Indicators of Compromise

Unexpected downgrades or protocol negotiation anomalies in TLS or system service traffic originating from macOS endpoints on untrusted networks.
macOS hosts communicating with unfamiliar gateways, proxies, or ARP entries that change frequently on shared network segments.
Sensitive fields such as tokens, cookies, or identifiers appearing in plaintext captures where encryption was expected.

Detection Strategies

Inventory macOS endpoints and flag systems running versions earlier than macOS Sequoia 15.8, macOS Tahoe 26.7, or macOS Golden Gate 27.
Correlate endpoint build numbers with network telemetry to identify vulnerable devices connecting to untrusted Wi-Fi or guest networks.
Baseline outbound service destinations per host and alert on new external endpoints reached by unpatched macOS systems.

Monitoring Recommendations

Enable network traffic logging on egress points serving BYOD and roaming macOS fleets.
Monitor for ARP spoofing, rogue DHCP, and unauthorized access point beacons in corporate wireless environments.
Alert on macOS software update deferrals that leave devices on affected builds beyond a defined SLA.

How to Mitigate CVE-2026-43787

Immediate Actions Required

Deploy macOS Sequoia 15.8, macOS Tahoe 26.7, or macOS Golden Gate 27 to all affected endpoints through MDM or Software Update.
Prioritize patching for devices that regularly connect to untrusted, public, or guest networks.
Verify installed build numbers post-deployment to confirm remediation.

Patch Information

Apple released fixes in macOS Golden Gate 27, macOS Sequoia 15.8, and macOS Tahoe 26.7. Refer to the vendor advisories: Apple Security Update 149035, Apple Security Update 149042, and Apple Security Update 149043.

Workarounds

Require corporate VPN for macOS clients when connected to untrusted networks to reduce exposure to on-path attackers.
Disable auto-join for open Wi-Fi networks and enforce Wi-Fi profiles that require WPA2/WPA3 Enterprise authentication.
Restrict use of shared and public networks for devices handling sensitive user data until patches are applied.

bash

# Verify macOS build version on affected endpoints
sw_vers

# Trigger software update check and install available updates
sudo softwareupdate --list
sudo softwareupdate --install --all --restart