Public PoC lands for macOS HFS+ kernel overflow triggered by a malicious disk image

A working proof-of-concept and a full technical write-up are now public for CVE-2026-43682, a kernel heap overflow in the HFS+ file system driver that Apple patched in macOS in July. Researcher Peter Malone published the details on October 5, roughly ten weeks after the fix shipped, turning a quietly patched memory-corruption bug into something any Mac still running an older build should treat as pressing.

What happened

Apple's advisory for macOS Tahoe 26.6, released on July 27, 2026, lists the issue under the "HFS" component and describes the impact as "a remote user may be able to cause unexpected system termination or corrupt kernel memory." Apple said "a buffer overflow was addressed with improved bounds checking," and credited the report to Trung Nguyen (@everping) of CyStack, Dave G., Nicolas Rabrenovic, Atul R V and Ashmit Sharma, and Peter Malone — an unusually long credit list, which indicates several researchers found the same defect independently.

According to SecurityOnline, which reported the publication, public vulnerability databases score the flaw 9.8. Apple does not assign CVSS ratings in its own advisories, so that figure comes from third parties rather than the vendor. SecurityOnline also noted that no exploitation in the wild has been confirmed.

Technical details

Malone's write-up places the bug in the way HFS+ walks the attributes B-tree, the structure that stores extended attributes. Per the repository, the code copies a record's key into a fixed BTreeKey structure with room for 522 bytes without first checking the key length against that buffer. A crafted disk image can declare an oversized key — the write-up describes one of roughly 2,900 bytes — that passes the initial validation and then overflows the destination during the memmove, corrupting the kernel heap. The missing check affected several B-tree routines, including BTSearchRecord, BTIterateRecord and BTIterateRecords.

The published proof-of-concept is a generator that builds such a malformed image. According to the repository, mounting the image and then listing extended attributes with ls -l@ is enough to walk into the vulnerable code and panic the kernel. Malone reproduced the crash on macOS Tahoe 26.3 with com.apple.filesystems.hfs.kext version 704.60.4.

Malone's timeline shows the bug was reported to Apple on March 8, 2026, earned a $20,000 bounty on April 23, and was fixed on July 27.

Who is affected

Apple fixed the issue in macOS Tahoe 26.6, macOS Sequoia 15.7.8 and macOS Sonoma 14.8.8, all released on July 27, 2026. Macs on earlier builds of those branches remain exposed. The reach of the bug is wider than HFS+ usage suggests: the driver is still present and loadable on current macOS even though APFS has long been the default file system, so a machine does not need an HFS+ volume of its own to parse an attacker's HFS+ image.

What to do

Update affected Macs to the July builds or later. Until that is done, the practical guidance is to avoid mounting disk images from untrusted sources. With a public proof-of-concept available, a .dmg arriving by email, download or a shared network volume is now a realistic route to a kernel panic at minimum, and a routine extended-attribute listing — or Spotlight indexing a freshly mounted volume — can be enough to reach the vulnerable code. Fleet administrators should also check whether mobile device management policies still allow users to mount arbitrary disk images, since that is the precondition the exploit depends on.