Bytes
The original encoded representation supplied to the parser.
PUBLIC RESEARCH / SYSTEMS SECURITYJEFFERY KIMBROW · PUBLISHED 2026-09-30
PASTDOOR
After BlastDoor: State Transformation Across Trusted System Services
BlastDoor confines parsing authority.
It does not terminate the state produced by parsing.
PASTDOOR follows that state as trusted system services reconstruct, synchronize, allocate, render, transmit, and act on it.
01 / INSIGHT
Parser containment
is not state containment.
BlastDoor constrains the authority under which untrusted message content is parsed. Accepted structured state can then be materialized by trusted consumers under different representations, invariants, and authority.
Semantic state
A device association, account relation, image dimension, or resource relationship retained across representation changes.
Consumer-local state
The local object reconstructed by a receiving service, evaluated under that service’s rules.
Manuscript: Introduction; State Transition Semantics.
02 / PAST THE DOOR
A boundary crossed.
A state transformed.
UNTRUSTED MESSAGE DOMAIN
State-bearing input P₀
State-bearing input P₀
BLASTDOORENTRY / ISOLATION BOUNDARY · PARSER AUTHORITY CONSTRAINED
PASTDOOR / TRUSTED CONSUMERS
Structured state S₀ Protobuf / XPC materialization W₁
Identity / pairing
Synchronization · prekeys · device relationships
Account and device authority
Image / graphics
ImageIOXPC → IOSurface → Metal / MPS
Shared memory and render authority
Network / accessory
Interface · iAP2 · UARP · endpoint state
Transport and update authority
Consumer-local representations Cᵢ · Local invariants Iᵢ
Runtime observations Oᵢ Evidence model ↗
THE TRANSITION
Representation changes.
Meaning can survive.
Accept
A state-bearing message reaches the BlastDoor parsing boundary.
Decode
BlastDoor produces structured state under constrained parser authority.
Materialize
Serialization and XPC reconstruct state for downstream consumers.
Reconstruct
Consumers combine transferred state with local or authoritative state.
Act
The receiver evaluates local invariants and acts using its own authority.
Manuscript: Post-BlastDoor Path Reconstruction.
THE STATE-TRANSFORMATION MODEL
Same meaning. Different local forms.
Provider representation + retained / reconstructed statePᵢ + Sᵢ
→Local transformationCᵢ = Tᵢ(Pᵢ, Sᵢ)
→Local invariant in context ΓᵢIᵢ(Cᵢ, Γᵢ)
→Observer-dependent effectOᵢ
Sᵢ ∼ Sⱼ while Cᵢ ≠ Cⱼ
Semantic correspondence does not require byte identity. Different consumers can reconstruct related state into different local representations and expose different failure phenotypes.
The manuscript defines Oᵢ = Ωᵢ(Cᵢ, Iᵢ(Cᵢ, Γᵢ)). Source: State Transition Semantics.
Retention
Rlocal(Sₜ) carries existing state across a lifecycle transition.
Reconstruction
Rremote(Aₜ, Dₜ) rebuilds state from account and device sources.
Hybrid
R(Sₜ, Aₜ, Dₜ) combines local and authoritative state.
THREE QUESTIONS / ONE ANALYSIS MODEL
Reachability
Which trusted consumer can receive state derived from the decoded input?
Transformation
How does that consumer serialize, reconstruct, materialize, synchronize, or transform the state?
Authority
What can that consumer change, allocate, synchronize, render, transmit, update, or otherwise act upon?
03 / MECHANISMS
Where consumers enforce their rules.
Implementation analysis and embedded diagnostics expose validation branches, assumptions, and failure paths. The excerpts below reproduce manuscript diagnostics.
A / SERIALIZATION & XPC
A new object at the receiving boundary.
Protobuf validates required fields and field types, detects concurrent mutation, and compares calculated and serialized byte counts. XPC requires an exported receiver and allowed protocol, and checks wire/local signature compatibility.
The decoder creates a new local object. Receiving interface rules govern its acceptance.
Inspect extracted protobuf and XPC diagnostics
EXTRACTED PROTOBUF DIAGNOSTICS (VERBATIM)
CHECK failed: (byte_size_before_serialization) ==
(byte_size_after_serialization):
Protocol message was modified concurrently during serialization.
CHECK failed: (bytes_produced_by_serialization) ==
(byte_size_before_serialization):
Byte size calculation and serialization were inconsistent.EXTRACTED XPC DIAGNOSTICS (VERBATIM)
received an undecodable message for proxy %lld
(no exported object to receive message). Dropping message.
received an undecodable message
(no protocol set to define allowed messages on exported object).
Dropping message.
received an undecodable message
(incompatible reply block signature for %s
(wire: %@ vs local: %@)B / IDENTITY, PAIRING & SYNCHRONIZATION
State rebuilt from authoritative relationships.
Services deserialize device public prekeys, check version and validity, and generate ephemeral P-256 keys for message sealing. Account and device relationships support reconstruction across process, device, and lifecycle boundaries.
Pass synchronization and companion relationships can recreate semantically related state after a process-local representation is gone.
Inspect extracted identity and prekey diagnostics
EXTRACTED IDENTITY AND PREKEY DIAGNOSTICS (VERBATIM)
Failed to deserialize the device public prekey.
Tetra version mismatch. Versions: Theirs: %u, Ours: %ld
Failed to encrypt to prekey that is no longer valid: %f.
Failed to generate an ephemeral P-256 key for message sealing.
The encryption of an outgoing message failed.C / IMAGE & GRAPHICS
From encoded media to resource authority.
ImageIOXPC decodes images; IOSurface supplies shareable backing. Metal and Metal Performance Shaders act on resources with allocation, lifetime, texture, region, heap, kernel, and matrix constraints. Rendering caches and framebuffer operations introduce further local state.
Inspect extracted graphics and allocator diagnostics
EXTRACTED GRAPHICS AND ALLOCATOR DIAGNOSTICS (VERBATIM)
TileEngineError: (%s,%s:%d) %@ "allocated fullSizeTexture nil"
TileEngineError: (%s,%s:%d) %@ "texture not set"
TileEngineError: (%s,%s:%d) %@ "outputROI.p0 cannot be negative"
TileEngineError: (%s,%s:%d) %@ "outputTexture nil, internal error"
FigMetalAllocator >>>> %s:
Cannot increase the ref count of a nil metal resource
FigMetalAllocator >>>> %s: Allocating %.1fMB metal buffer from IOSurfacePencoded→Cimage→Csurface→Cresource→Ctexture→Orender
D / NETWORKING & ACCESSORY
Host state becomes endpoint state.
Link-quality and analytics mechanisms materialize interface and session state. iAP2-facing services and UARP restore/update surfaces translate between host, transport, firmware, and accessory representations, as well as asset-management services.
The paper identifies UARP as a restore/update surface; it does not identify RTKit here, so these remain distinct.
Inspect extracted UARP failure diagnostics
EXTRACTED UARP FAILURE DIAGNOSTICS (VERBATIM)
Timed out or aborted
Rejected
Not supported message received
UARP Restore: Failed to remove endpoint, status 0x%08xManuscript: Implementation Mechanisms, subsections A–D. These excerpts are implementation diagnostics; on their own, they do not establish a runtime event or its cause.
04 / EVIDENCE
Mechanism. Observation. Causal join.
A mechanism exists
Implementation analysis establishes a mechanism, invariant, validation path, or local failure condition.
An effect occurred
A runtime artifact establishes an observed operational effect.
The endpoints connect
An identifier, transfer, state transition, schema instance, or independent artifact connects specific endpoints.
The paper establishes downstream mechanisms, representation transformations, consumer authority, corresponding runtime effects, and semantic-state continuation capability. It does not establish universal per-input runtime attribution.
Paper: Claim Architecture; Attribution Boundary; Conclusion.
Recorded downstream operational domains
Manuscript: Recorded Runtime Consequences. These are recorded domains; co-occurrence does not establish a causal join.
RESEARCH CONTEXT
The point of departure.
PASTDOOR focuses on accepted semantic state after parser containment. The manuscript situates that analysis alongside earlier work on entry, exploit progression, mitigation crossing, and cross-abstraction effects.
- FORCEDENTRY
- Remote parser exploitation and the subsequent sandbox-escape stage.
- BLASTPASS
- PassKit attachments carrying malicious images through iMessage.
- PWNYOURHOME / FINDMYPWN
- Cross-service composition preceding an iMessage/BlastDoor phase.
- Operation Triangulation
- Multi-stage progression across processes and protection layers.
- PACMAN / Spectre
- Mitigation-crossing and cross-abstraction security comparators.
These are research comparators, with distinct mechanisms. See Related Work and its references in the paper.
05 / PAPER
PASTDOOR
After BlastDoor: State Transformation Across Trusted System Services
PUBLICATION / 2026-09-30
Jeffery Kimbrow
Independent Research
Citation: Kimbrow, J. (2026). PASTDOOR: After BlastDoor: State Transformation Across Trusted System Services. Zenodo. https://doi.org/10.5281/zenodo.23056249.
TECHNICAL FAQ
Questions at the boundary.
What is PASTDOOR?
A study of semantic-state continuation beyond BlastDoor: accepted state remains actionable as trusted consumers reconstruct it under new representations, invariants, and authority.
Is it the same mechanism as FORCEDENTRY or BLASTPASS?
No. The manuscript uses these as entry and exploit-progression comparators. PASTDOOR’s analysis target is accepted semantic state after parser containment.
Why does the analysis continue beyond BlastDoor?
Parser isolation limits immediate parsing authority. Downstream services still reconstruct accepted state and act under their own authority.
What does semantic state mean? Does it require identical bytes?
It is security-relevant meaning such as an account relation, device association, image property, or resource relationship. Semantic correspondence can survive different bytes and different consumer-local objects.
Does PASTDOOR attribute every downstream event to one message?
See the evidence model and attribution boundary for the manuscript’s distinction between implementation evidence, runtime observations, and per-event causal joins.
Does recurrence automatically prove persistence?
No. Recurrence after deletion or restart is compatible with local retention, authoritative reconstruction, or a hybrid. The mechanisms are local retention, authoritative reconstruction, and a hybrid of both.
Why do trusted consumers matter?
Each receiver can reconstruct state under new local rules and exercise authority over account relationships, shared memory, graphics resources, transport, updates, or accessories.
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