docs: add Iceberg security model (#3425)

Similar to: apache/iceberg#16538

This PR publishes a security model for Iceberg and adds a detailed
threat model referenced from AGENTS.md so there is a clear project
reference for how Iceberg distinguishes security issues from other bugs.

The goal is to make Iceberg’s security boundaries explicit for both
human triage and automated scanning, and to reduce false positives in
future security reporting.

This PR was drafted with AI assistance and then manually reviewed and
edited to reflect the project’s current approach to security roles,
trust boundaries, and the handling of recent security reports.

Author: sungwy

AGENTS.md

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+<!--
+  Licensed to the Apache Software Foundation (ASF) under one
+  or more contributor license agreements.  See the NOTICE file
+  distributed with this work for additional information
+  regarding copyright ownership.  The ASF licenses this file
+  to you under the Apache License, Version 2.0 (the
+  "License"); you may not use this file except in compliance
+  with the License.  You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing,
+  software distributed under the License is distributed on an
+  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+  KIND, either express or implied.  See the License for the
+  specific language governing permissions and limitations
+  under the License.
+-->
+
+# Apache Iceberg Python — Agent Instructions
+
+This file provides repository-specific guidance for automated agents working
+in this repository.
+
+## Security Model
+
+When assessing potential vulnerabilities or calibrating automated security
+findings, use [`SECURITY-THREAT-MODEL.md`](SECURITY-THREAT-MODEL.md) as the
+authoritative detailed description of this repository's security boundaries,
+trust assumptions, and non-boundaries.

SECURITY-THREAT-MODEL.md

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+<!--
+  Licensed to the Apache Software Foundation (ASF) under one
+  or more contributor license agreements.  See the NOTICE file
+  distributed with this work for additional information
+  regarding copyright ownership.  The ASF licenses this file
+  to you under the Apache License, Version 2.0 (the
+  "License"); you may not use this file except in compliance
+  with the License.  You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing,
+  software distributed under the License is distributed on an
+  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+  KIND, either express or implied.  See the License for the
+  specific language governing permissions and limitations
+  under the License.
+-->
+
+# Apache Iceberg Python Security Threat Model
+
+This document describes the detailed security threat model for Apache
+Iceberg Python. It is intended for maintainers and automated security triage.
+
+## Purpose
+
+Apache Iceberg Python is primarily a client library and implementation of the
+Iceberg table format and catalog interactions for Python applications and
+services. It is commonly embedded in larger systems that provide their own
+authentication, authorization, and credential management. Because of that
+deployment model, many bug classes that look security-relevant in the abstract
+are not actually security vulnerabilities in Iceberg Python itself.
+
+This model is intended to answer:
+
+- what Iceberg Python generally treats as a security vulnerability
+- what Iceberg Python generally treats as correctness, hardening, or
+  deployment work
+- which boundaries are primarily owned by Iceberg Python versus the
+  surrounding catalog, application, or service
+- which issue classes should be downgraded by default by scanners
+
+## Scope
+
+This model is scoped to the Apache Iceberg Python repository itself:
+
+- table format and metadata handling
+- catalog and REST catalog clients
+- transport, credential, and configuration handling implemented in this repo
+- helper tooling shipped in this repo
+
+It is not a general threat model for every Python service that embeds Iceberg
+Python.
+
+In particular, it does not attempt to define the complete security model for:
+
+- applications or services that embed Iceberg Python
+- storage-level authorization enforced outside Iceberg Python
+
+## Security Goals
+
+Iceberg Python should:
+
+- avoid exposing secrets or delegated credentials to principals that were not
+  already trusted with them
+- avoid creating new unauthorized capabilities in Iceberg Python-owned
+  components
+- avoid violating trust boundaries that Iceberg Python itself owns, such as
+  leaking auth, transport, or credential-bearing state across catalog or
+  client boundaries in the same process
+
+Iceberg Python does not aim to be the primary enforcement point for:
+
+- user-to-user authorization inside the embedding application
+- storage-level authorization
+- service-side credential scoping performed by an external catalog
+
+## Roles
+
+### Operator
+
+The operator configures the surrounding catalog, application, service, and
+storage integration around Iceberg Python. This role is trusted to choose
+endpoints, warehouses, storage integrations, and credentials.
+
+### Catalog control plane
+
+The catalog control plane resolves tables and supplies metadata, locations,
+configuration, and delegated credentials to Iceberg Python. It may be
+implemented by a REST catalog server or another catalog implementation.
+Iceberg Python assumes this control plane is trusted and outside its primary
+security boundary.
+
+### REST catalog client
+
+The REST catalog client consumes catalog-provided metadata, configuration, and
+credentials. Client-side bugs in routing, caching, or reuse may still be
+security-relevant if they leak credential-bearing state across boundaries that
+the Iceberg Python client is expected to preserve.
+
+### Embedding application
+
+Applications and services embedding Iceberg Python are responsible for their
+own user-facing authorization boundaries unless Iceberg Python explicitly
+documents otherwise.
+
+### Table writer or maintainer
+
+This role may already have legitimate power to write or replace table
+metadata, write or delete files, choose paths under an allowed warehouse or
+table location, and invoke destructive maintenance operations. If a report
+only shows a new way to achieve the same effect this role can already cause
+legitimately, it is usually not a security issue in Iceberg Python.
+
+## Trust Boundaries
+
+### Boundary 1: operator-trusted configuration
+
+The following are generally treated as trusted operator or deployment inputs:
+
+- catalog properties
+- endpoint configuration
+- warehouse and storage roots
+- transport wiring and credential configuration
+
+If a report depends on the attacker controlling those values directly, it is
+usually not a vulnerability in Iceberg Python itself.
+
+### Boundary 2: catalog-supplied metadata
+
+Iceberg Python often accepts metadata locations, table properties, namespace
+properties, and related control-plane information from a catalog. By default,
+Iceberg Python treats those sources as trusted.
+
+This means a malicious catalog supplying incorrect or malicious metadata is
+usually not an Iceberg Python vulnerability by itself.
+
+### Boundary 3: REST catalog-supplied configuration and delegated storage access
+
+In REST deployments, Iceberg Python may also accept service endpoints,
+configuration, and delegated storage access from the REST catalog server. By
+default, those are treated as trusted control-plane inputs unless Iceberg
+Python explicitly documents a stronger guarantee.
+
+This means a malicious REST catalog server sending dangerous endpoints is
+usually not an Iceberg Python vulnerability by itself. It also means many
+credential-selection bugs are often correctness or specification issues rather
+than security boundary failures.
+
+The major exception is secret exposure. If Iceberg Python surfaces credentials
+or secrets to a new audience that was not already trusted with them, that is
+security-relevant.
+
+### Boundary 4: storage-level authorization
+
+Object store permissions are enforced by the storage provider and the
+credentials the surrounding deployment chooses to hand to Iceberg Python.
+Iceberg Python is not the root authority for bucket- or object-level
+authorization.
+
+## In-Scope Security Vulnerabilities
+
+The following categories are generally security-relevant in Iceberg Python
+when the report is credible and reproducible.
+
+### 1. Secret or credential disclosure to a new audience
+
+Examples include:
+
+- catalog or storage credentials exposed through a user-visible surface
+- one catalog's credentials or auth state leaking into another catalog or
+  client
+
+### 2. Iceberg Python-owned trust-boundary violations
+
+Security issues exist when Iceberg Python itself is expected to separate
+catalogs, clients, or principals and fails to do so.
+
+Examples include:
+
+- process-global auth or transport state crossing catalog instances
+- secret-bearing state from one principal reused for another principal within
+  an Iceberg Python-owned boundary
+
+## Usually Out of Scope or Non-Security by Default
+
+These categories may still be real bugs worth fixing, but they are not usually
+security vulnerabilities in Iceberg Python itself.
+
+### 1. Correctness bugs
+
+Examples include incorrect metadata handling, ambiguous matching semantics,
+and logic bugs that do not create a new trust-boundary violation.
+
+### 2. Parser hardening and malformed-input robustness
+
+Malformed-input crashes, runtime exceptions, and memory amplification are
+usually treated as robustness or hardening work rather than security issues in
+Iceberg Python itself.
+
+### 3. Malicious catalog or external service scenarios
+
+Reports that require a malicious catalog or other external control-plane
+service are usually outside Iceberg Python's primary security boundary.
+
+### 4. Equivalent-harm reports
+
+If the actor already has a legitimate capability that can cause the same harm,
+the new path is usually not a security issue.
+
+## Scanner Calibration Rules
+
+A scanner targeting Iceberg Python should treat a finding as higher-confidence
+only if it plausibly shows one of the following:
+
+- exposure of a secret or delegated credential to a new audience
+- creation of a new unauthorized capability in an Iceberg Python-owned
+  component
+- violation of an Iceberg Python-owned trust boundary rather than a
+  surrounding catalog, application, service, or operator boundary
+
+A finding should be downgraded or rejected by default if it instead depends
+primarily on:
+
+- malformed-input robustness or denial-of-service behavior
+- a malicious catalog or external service
+- a principal that already has equivalent power through legitimate write or
+  maintenance capabilities