CVE-2026-39877 Overview
CVE-2026-39877 is a memory corruption vulnerability in Apple macOS that allows a local application to disclose kernel memory. Apple addressed the issue with improved memory handling in macOS Sequoia 15.7.8 and macOS Sonoma 14.8.8. The vulnerability is classified under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer) and requires local access with user interaction to exploit.
Critical Impact
A malicious application running on a vulnerable macOS host can read kernel memory, exposing sensitive data such as pointers, credentials, and cryptographic material that support further privilege escalation attacks.
Affected Products
- Apple macOS Sequoia versions prior to 15.7.8
- Apple macOS Sonoma versions prior to 14.8.8
- Applications with local execution on affected macOS builds
Discovery Timeline
- 2026-07-27 - CVE-2026-39877 published to NVD
- 2026-07-29 - Last updated in NVD database
Technical Details for CVE-2026-39877
Vulnerability Analysis
The vulnerability resides in kernel-level memory handling routines within macOS. A local application can trigger the flaw to read memory regions belonging to the kernel address space. Apple's advisory attributes the fix to improved memory handling, indicating the original code failed to correctly bound or initialize memory before returning data to user space.
Kernel memory disclosure primitives are frequently chained with additional bugs to defeat Kernel Address Space Layout Randomization (KASLR) and stage privilege escalation. Attackers use leaked pointers to compute kernel base addresses, locate structures, and craft reliable follow-on exploits. The [CWE-119] classification aligns with an out-of-bounds read or a similar buffer boundary failure.
Root Cause
The root cause is improper restriction of memory buffer operations in a macOS kernel component. Apple's remediation language describes an unspecified memory corruption issue corrected through improved memory handling, consistent with a boundary check failure or an initialization gap that returns kernel-resident bytes to a userspace caller.
Attack Vector
Exploitation requires local code execution on the target macOS system and user interaction, based on the CVSS vector. An attacker delivers a malicious application, or leverages an existing low-privilege process, that invokes the vulnerable kernel interface. The application then reads kernel memory contents that should not be accessible to userspace. See Apple's advisories for details on affected components at Apple Support Article 128071 and Apple Support Article 128072.
Detection Methods for CVE-2026-39877
Indicators of Compromise
- Unsigned or ad-hoc signed binaries invoking low-level system calls or IOKit interfaces from non-standard paths such as /tmp, /private/var/tmp, or user Library directories.
- Repeated kernel-log entries or panics originating from a single userspace process, indicating fuzzing or exploitation attempts.
- Newly installed applications requesting elevated entitlements shortly before anomalous kernel activity.
Detection Strategies
- Monitor process telemetry for userspace binaries issuing high volumes of Mach traps, IOKit calls, or sysctl queries associated with kernel memory access.
- Correlate application execution events with kernel diagnostic reports in /Library/Logs/DiagnosticReports/ to identify probing activity.
- Baseline installed applications and alert on macOS binaries that lack notarization but interact with kernel extensions.
Monitoring Recommendations
- Ingest Endpoint Security framework events for es_event_exec_t and es_event_open_t targeting kernel-related paths.
- Track macOS build versions across the fleet and flag hosts running builds older than 15.7.8 (Sequoia) or 14.8.8 (Sonoma).
- Alert on privilege elevation events that follow suspicious application launches within short time windows.
How to Mitigate CVE-2026-39877
Immediate Actions Required
- Update all macOS Sequoia hosts to 15.7.8 and macOS Sonoma hosts to 14.8.8 without delay.
- Inventory endpoints running unsupported or older macOS releases and prioritize them for upgrade or isolation.
- Restrict installation of untrusted applications through Gatekeeper, notarization enforcement, and MDM application allowlists.
Patch Information
Apple released fixes in macOS Sequoia 15.7.8 and macOS Sonoma 14.8.8. Full advisory details are available at Apple Support Article 128071 and Apple Support Article 128072. No official workaround exists that fully mitigates the issue without applying the update.
Workarounds
- Limit local execution on affected hosts by enforcing least-privilege user accounts and removing unnecessary administrative rights.
- Enable System Integrity Protection (SIP) and require notarized applications through Gatekeeper configuration.
- Deploy application control policies via Mobile Device Management (MDM) to block execution of unapproved binaries until patching is complete.
# Verify macOS build version on affected endpoints
sw_vers -productVersion
# Trigger the built-in software update mechanism
sudo softwareupdate --install --all --restart
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
