CVE-2026-43777: Apple macOS Denial of Service Vulnerability

CVE-2026-43777 Overview

CVE-2026-43777 is an improper input validation vulnerability [CWE-20] affecting Apple macOS. A remote attacker can trigger a denial of service condition by sending crafted input that bypasses validation routines in the affected component. Apple addressed the issue with improved input validation in macOS Sequoia 15.7.8, macOS Sonoma 14.8.8, and macOS Tahoe 26.6.

The vulnerability is network-exploitable, requires no privileges, and requires no user interaction. Successful exploitation impacts availability without compromising confidentiality or integrity.

Critical Impact
A remote, unauthenticated attacker can cause a denial of service on unpatched macOS systems by delivering malformed input over the network.

Affected Products

Apple macOS Sequoia versions prior to 15.7.8
Apple macOS Sonoma versions prior to 14.8.8
Apple macOS Tahoe versions prior to 26.6

Discovery Timeline

2026-07-27 - CVE-2026-43777 published to NVD
2026-07-28 - Last updated in NVD database

Technical Details for CVE-2026-43777

Vulnerability Analysis

CVE-2026-43777 is classified as an Improper Input Validation weakness [CWE-20]. The affected macOS component fails to adequately validate incoming data before processing it. An attacker who submits malformed or unexpected input over the network can drive the component into an error state that results in denial of service.

Apple's advisories state the issue was addressed with improved input validation. The fix hardens the parsing or handling logic to reject or safely process the malformed input that previously caused the fault. Refer to the Apple Support Advisory #128067, Apple Support Advisory #128071, and Apple Support Advisory #128072 for vendor guidance.

Root Cause

The root cause is missing or insufficient validation of attacker-controlled input in a network-reachable macOS component. Apple has not published low-level technical details of the flawed routine. The vendor description confirms the fix category is input validation, indicating the vulnerable code accepted data outside the expected structure, length, or type.

Attack Vector

An attacker delivers a crafted network payload to a vulnerable macOS host. No authentication or user interaction is required. The malformed input triggers the validation failure and produces a denial of service. Confidentiality and integrity are not affected. No public proof-of-concept or in-the-wild exploitation has been reported.

No verified exploit code is publicly available for CVE-2026-43777. See the vendor advisories linked above for authoritative details.

Detection Methods for CVE-2026-43777

Indicators of Compromise

Unexpected service crashes, kernel panics, or system reboots on macOS endpoints that correlate with inbound network traffic.
Repeated malformed packets or protocol anomalies directed at macOS hosts prior to service disruption.
Diagnostic reports in /Library/Logs/DiagnosticReports/ referencing the affected component around the time of the outage.

Detection Strategies

Monitor macOS system logs via log show and unified logging for repeated crash signatures on network-facing daemons.
Correlate network IDS alerts for malformed protocol traffic with endpoint availability events on macOS assets.
Track macOS build versions in your asset inventory and flag hosts running versions earlier than 15.7.8, 14.8.8, or 26.6.

Monitoring Recommendations

Alert on abnormal restart or crash frequency for macOS endpoints, particularly in server or shared-workstation roles.
Baseline inbound network traffic to macOS hosts and alert on volumetric or malformed traffic bursts.
Ingest macOS endpoint telemetry into your SIEM or data lake to correlate crashes with attacker-controlled network sources.

How to Mitigate CVE-2026-43777

Immediate Actions Required

Update all Apple macOS endpoints to macOS Sequoia 15.7.8, macOS Sonoma 14.8.8, or macOS Tahoe 26.6 or later.
Inventory macOS assets and prioritize patching internet-exposed or high-availability systems first.
Validate patch deployment by confirming the OS build version on each managed macOS host.

Patch Information

Apple released fixes in macOS Sequoia 15.7.8, macOS Sonoma 14.8.8, and macOS Tahoe 26.6. Consult the Apple Support Advisory #128067, Apple Support Advisory #128071, and Apple Support Advisory #128072 for the specific advisory matching each macOS train.

Workarounds

Restrict inbound network exposure to macOS hosts using host and perimeter firewalls until patches are applied.
Disable or filter access to non-essential network services on macOS endpoints.
Segment macOS assets from untrusted networks to reduce the attack surface for remote unauthenticated attackers.

bash

# Verify installed macOS version
sw_vers -productVersion

# Trigger a software update check on managed macOS endpoints
sudo softwareupdate --list
sudo softwareupdate --install --all --restart