Security firm Calif has released technical details of the two macOS vulnerabilities it used to break Apple's Memory Integrity Enforcement (MIE) — and rather than save the exploit for its Black Hat talk, the company is handing the bugs to the public as an open contest for human and AI researchers alike.
Both flaws were fixed in macOS Tahoe 26.6, which Apple shipped on July 27. Users still running earlier builds should update now.
Calif first demonstrated the bypass in May against macOS 26.4.1 on Apple M5 silicon, the debut chip for MIE — Apple's hardware-backed memory safety layer built on ARM's Memory Tagging Extension, and the product of roughly five years of engineering.
The firm withheld details until patches landed, and says it has reported 38 vulnerabilities to Apple since March. According to the write-up, getting from bug discovery to a working exploit chain took about 5 days.
Apple's own advisory offers a notable detail: the SMB fix credits Calif.io in collaboration with Claude and Anthropic Research, alongside researchers from Cisco Talos and others.
The two bugs
CVE-2026-64704 is a type confusion in SMBClient. When macOS asks a server to resolve an inode number to a path, the kernel builds one kind of structure, but the reply parser decides what that structure is based purely on a four-byte tag the server sends back. A malicious SMB server answers with a lease tag instead, and the kernel reinterprets an attacker-influenced 64-bit value as a pointer — then dereferences it.
CVE-2026-64699 is the matching info leak in the WebDAV kernel extension. A stalled download pushes reads down an out-of-band path that allocates a large buffer without zeroing it. A server replying with an empty HTTP 206 response counts as success, and the kext copies the full requested length back to userspace — including stale kernel memory.
The challenge
Calif is inviting anyone to chain the two into a root shell on a fully MIE-enabled Mac before it presents its own approach at Black Hat USA on August 5. The company frames modern XNU exploitation as "one of the hardest and most interesting benchmarks for AI-assisted exploit development." Humans, AI systems, and mixed teams are all welcome.
What to do: install macOS Tahoe 26.6. Both bugs require the victim to mount a share from an attacker-controlled server, so avoid connecting to untrusted SMB or WebDAV endpoints — and consider blocking outbound SMB at the network edge.