CVE-2026-84559: Apple macOS Privilege Escalation Flaw

CVE-2026-84559 Overview

CVE-2026-84559 is a permissions validation flaw in Apple macOS that allows a malicious application to access restricted files. Apple addressed the issue with improved validation in macOS Golden Gate 27, macOS Sequoia 15.8, and macOS Tahoe 26.7. The weakness is categorized under [CWE-693] (Protection Mechanism Failure), reflecting a bypass of intended access controls rather than a code execution primitive. Local access is required, and exploitation yields disclosure of files that should be gated by macOS sandbox or Transparency, Consent, and Control (TCC) protections.

Critical Impact
A locally installed malicious application can read restricted files on affected macOS systems, exposing sensitive user or system data protected by macOS permission controls.

Affected Products

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

Discovery Timeline

2026-09-14 - CVE-2026-84559 published to the National Vulnerability Database (NVD)
2026-09-17 - Last updated in the NVD database

Technical Details for CVE-2026-84559

Vulnerability Analysis

The vulnerability stems from insufficient validation of permission checks within macOS. An application executing on the local system can leverage the flaw to reach files that fall outside the boundaries enforced by macOS access controls. Because the attack requires local execution and low privileges, the practical scenario involves an application the user has already installed or launched, whether unwittingly downloaded or delivered through another vector.

Apple's advisory states that the issue was corrected with improved validation. This language typically indicates that the protection mechanism failed to consistently enforce entitlements, sandbox restrictions, or TCC prompts before granting file access. The confidentiality impact is high while integrity and availability are unaffected, aligning with a read-only disclosure primitive.

Root Cause

The root cause is a Protection Mechanism Failure [CWE-693] in a macOS component that gates access to restricted files. The pre-patch code path did not validate a caller's permissions with sufficient rigor, allowing a request to succeed against a resource that should have been blocked by the operating system's access control layer.

Attack Vector

Exploitation requires a local, authenticated context. An attacker must first place and run code on the target macOS host, for example through a malicious application distributed via social engineering, supply chain compromise, or a bundled installer. Once running, the application invokes the affected API path or file operation to retrieve data it should not be authorized to read. No user interaction is required beyond initial execution.

Apple has not published exploit technical details, and no public proof-of-concept has been observed in reference sources. Readers should consult the vendor advisories linked below for scope specifics: Apple Support Document #149035, Apple Support Document #149042, and Apple Support Document #149043.

Detection Methods for CVE-2026-84559

Indicators of Compromise

Unsigned or ad-hoc signed applications launching from user-writable paths such as ~/Downloads, ~/Library, or /tmp and subsequently reading files outside their sandbox container.
Access attempts to TCC-protected locations (for example ~/Library/Mail, ~/Library/Messages, ~/Library/Application Support) by processes without corresponding entitlements.
Unexpected reads of keychain files, browser profile directories, or SSH key material by non-system binaries.

Detection Strategies

Monitor Endpoint Security framework (ES_EVENT_TYPE_NOTIFY_OPEN) telemetry for file opens targeting restricted paths by processes lacking the expected code signature or entitlements.
Baseline application file-access patterns and alert on deviations, particularly reads spanning multiple user data directories in a short window.
Correlate application install events with subsequent file access to identify newly deployed binaries exhibiting reconnaissance-style file enumeration.

Monitoring Recommendations

Ingest macOS Unified Log entries related to tccd, sandboxd, and kernel sandbox denials to identify probing behavior around the patch window.
Track macOS build versions across the fleet and flag hosts still running pre-patch releases of Sequoia, Tahoe, or Golden Gate.
Enable file integrity and access monitoring on directories containing credentials, browser data, and mail stores.

How to Mitigate CVE-2026-84559

Immediate Actions Required

Install macOS Golden Gate 27, macOS Sequoia 15.8, or macOS Tahoe 26.7 on all affected endpoints without delay.
Restrict installation of third-party applications to those from trusted developers and the Mac App Store using Gatekeeper policy.
Audit recently installed applications for unexpected file access behavior and remove any unverified software.

Patch Information

Apple released fixes in macOS Golden Gate 27, macOS Sequoia 15.8, and macOS Tahoe 26.7. The corresponding advisories are Apple Support Document #149035, Apple Support Document #149042, and Apple Support Document #149043. Patching is the only vendor-supported remediation.

Workarounds

Enforce least privilege on end-user accounts and avoid granting administrator rights to daily-use profiles.
Deploy application allowlisting through mobile device management (MDM) policies to block execution of unapproved binaries.
Configure TCC and Full Disk Access policies via MDM to explicitly deny sensitive data access to non-essential applications until patching is complete.

bash

# Verify installed macOS version against patched builds
sw_vers -productVersion

# Check for pending Apple software updates and install them
softwareupdate --list
sudo softwareupdate --install --all --restart