CVE-2026-39870: Apple macOS Buffer Overflow Vulnerability

CVE-2026-39870 Overview

CVE-2026-39870 is a memory corruption vulnerability affecting Apple macOS image processing components. Processing a maliciously crafted image can corrupt process memory, leading to potential information disclosure or application instability. The flaw is classified under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer).

Apple addressed the issue with improved memory handling in macOS Sequoia 15.7.7, macOS Sonoma 14.8.7, and macOS Tahoe 26.5. The vulnerability is remotely reachable through any vector that delivers an image to a vulnerable parser, including web browsing, messaging applications, and email clients. No authentication or user interaction beyond opening the image is required.

Critical Impact

Remote attackers can trigger memory corruption in macOS image processing by delivering a crafted image, with confidentiality impact on affected systems.

Affected Products

• Apple macOS Sequoia (prior to 15.7.7)
• Apple macOS Sonoma (prior to 14.8.7)
• Apple macOS Tahoe (prior to 26.5)

Discovery Timeline

• 2026-05-11 - CVE-2026-39870 published to NVD
• 2026-05-13 - Last updated in NVD database

Technical Details for CVE-2026-39870

Vulnerability Analysis

The vulnerability resides in macOS image processing code that fails to properly validate buffer boundaries when parsing crafted image data. When the affected parser handles malformed input, internal memory structures can be overwritten, corrupting process memory state.

Apple's advisory describes the fix as "improved memory handling," indicating that the original code path performed insufficient bounds checking on attacker-controlled fields within the image format. The flaw falls under [CWE-119], covering improper restriction of operations within memory buffer bounds.

The EPSS probability for this CVE is 0.04%, placing it in the 12th percentile of vulnerabilities by likelihood of near-term exploitation. No public proof-of-concept code is available, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog.

Root Cause

The root cause is improper bounds validation in an image decoding routine. Crafted metadata or pixel data fields cause the parser to read or write outside the intended buffer, corrupting adjacent memory regions within the process address space.

Attack Vector

The attack vector is network-based and requires no privileges. An attacker hosts or transmits a malicious image, and the target processes it through any application that relies on the vulnerable macOS image framework. Common delivery channels include web pages, instant messages, email attachments, and shared documents. Apple has not published technical details of the affected parser. Refer to Apple Support Document 127115, Apple Support Document 127116, and Apple Support Document 127117 for vendor-supplied information.

Detection Methods for CVE-2026-39870

Indicators of Compromise

• Unexpected crashes or abnormal terminations in applications that render images, with diagnostic reports referencing image decoding frameworks.
• Receipt of image files from untrusted sources containing malformed headers, oversized dimensions, or inconsistent metadata fields.
• Anomalous memory access violations recorded in macOS unified logs from processes that handle untrusted media.

Detection Strategies

• Inspect crash reports in /Library/Logs/DiagnosticReports/ for signatures pointing to image parsing libraries.
• Deploy endpoint telemetry to record process crashes correlated with image file access events.
• Use network inspection to flag unusual image payloads delivered through messaging, email, or web traffic.

Monitoring Recommendations

• Monitor macOS endpoints for repeated crash signatures in image-handling processes that may indicate exploitation attempts.
• Track software inventory to confirm all macOS hosts are upgraded to patched versions.
• Correlate image file delivery events with subsequent process anomalies through centralized logging.

How to Mitigate CVE-2026-39870

Immediate Actions Required

• Upgrade affected systems to macOS Sequoia 15.7.7, macOS Sonoma 14.8.7, or macOS Tahoe 26.5.
• Verify update deployment status across the fleet using MDM or configuration management tooling.
• Restrict opening of images from untrusted sources until patching is complete.

Patch Information

Apple released fixes in macOS Sequoia 15.7.7, macOS Sonoma 14.8.7, and macOS Tahoe 26.5. The vendor describes the remediation as improved memory handling within the affected image processing code. Patch details are available in Apple Support Document 127115, Apple Support Document 127116, and Apple Support Document 127117.

Workarounds

• Disable automatic image previews in messaging and email clients where feasible until patches are applied.
• Block delivery of high-risk image MIME types at email and web gateways for unpatched hosts.
• Limit user permissions to reduce post-exploitation impact if a process is compromised.

# Verify macOS version on affected endpoints
sw_vers -productVersion

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