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Prompt Injection: Blast Radius

Prompt Injection: Blast Radius

Building AI agents that can't be talked into anything.

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September 16, 2026

Contents

1
The Three-Year Bug
2
Why the industry shipped anyway
3
Injection Is Not Jailbreaking
4
Why the confusion persists
5
The Lethal Trifecta
6
Running the audit
7
Why Filtering Fails
8
Measured here, on a named model
9
Why this is structural
10
What “Solved” Would Look Like
11
The harness
12
Provenance: Every Value Knows Where It Came From
13
On the reference agent
14
Quarantine: The Planner Never Reads the Mail
15
What two models cost in practice
16
Capability: Authority the Agent Cannot Widen
17
Expiry is a feature
18
The Gate: The Model Proposes, Code Disposes
19
The policy
20
Failing closed
21
Egress: Closing the Exfiltration Leg
22
How much can actually leak
23
Sandboxing: Containing the Code the Agent Writes
24
The sandbox held and it did not help
25
Poisoned Memory, Poisoned Retrieval
26
Cleaning up afterwards
27
The Tool Supply Chain
28
MCP and the rest
29
Human-in-the-Loop That Isn't Theatre
30
When there is nobody there
31
Testing for Injection
32
Measuring coverage, not pass rate
33
Red Teaming Agents
34
A finding, worked through
35
When It Happens Anyway
36
What the logs cost you in an incident you did not have
37
Governance, Procurement and the Regulator
38
Writing the policy
39
End to End
40
What it actually took
41
What Stays Broken
42
Why this is probably structural
43
The Trifecta Audit Worksheet
44
Action Schema and Policy Reference
45
Control Mapping
46
Sources
47
Incidents
48
Appendix E: What We Re-Ran Ourselves
49
E.4 The control that keeps E.2 and E.3 honest

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