CVE-2026-43813 — CloudAttestation enforceEnvironment bypass

Reverse-engineered analysis of the PCC attestation input-validation bug Apple shipped as iOS 26.6, found in CloudAttestation.dylib.

TL;DR

PCC.ComputeNodeValidator.policy.getter reads the com.apple.CloudAttestation.environment byte from the unverified darwinInit dictionary inside the AttestationBundle protobuf and stuffs it straight into the NodeValidator.policy returned to the caller. The 26.6 fix introduces a new struct field that is supposed to gate that read on the system policy key enforceEnvironment in the com.apple.CloudAttestation domain — but that field was never initialised in 26.5, so the gate was effectively absent and a crafted PCC attestation bundle could set an attacker-chosen environment value into the validator's policy chain.

The byte itself doesn't unlock anything by itself — it has to match the caller-supplied expected parameter to pass EnvironmentPolicy.evaluate, and the rest of the production policy stack (requireProdTrustAnchors, requireProdFusing, requireLockedCryptexes, restrictDeveloperMode, strictCertificateValidation, transparencyProofValidation, ensembleTopologyValidation) is read from os_policy_lookup, not from the bundle.

Binaries included in the repo

IDA databases (.i64), BinExport dumps, and other in-between builds are gitignored.

Vulnerable / patched addresses

Bindiff similarity for the patched pair: 0.68.

Files

• WRITEUP.md — full reverse-engineering writeup (data flow, fix patch, why it's PCC-internal not app-signing-internal)
• WHY-NOT-SIDELOADING.md — short threat-model coda explaining why this CVE can't be turned into a TrollStore-style exploit
• NOTES.md — analysis scratchpad
• CVE-2026-43813.txt — original CVE description (verbatim from VulDB)
• releases.txt — build IDs in chronological order

Note

This research was heavily assisted by MiniMax-M3. Keep that in mind when reading the writeups — none of the analysis is independently verified, and any quoted decompilation, address, or similarity score should be re-checked before relying on it.