Hallucination as Exploit: Evidence-Carrying Multimodal Agents

Guijia Zhang, Hao Zheng, Harry Yang


Abstract
Multimodal agents increasingly choose tool calls from screenshots, documents, and webpages, where a false perceptual claim can turn hallucination from an answer-quality error into an authorization failure. We formalize this failure as hallucination-to-action conversion (H2AC) and propose evidence-carrying multimodal agents (ECA), in which model text may propose actions but cannot authorize them: constrained DOM/OCR/AX verifiers issue typed certificates for action-critical predicates, and a deterministic gate executes only what the certificates support. Across verifier red-teaming, 7,488 replayed authorization traces, and end-to-end and live-browser evaluations, ECA executes no unsafe action, while GPT-5.4 judge baselines admit 79–99% of unsafe actions under the same threat model; benign actions are occasionally deferred to user confirmation (6.4% on live pages) but never hard-blocked. The guarantee is conditional, extending exactly as far as the verifiers, schemas, and gate implementation that form ECA’s trusted base.
Anthology ID:
2026.findings-emnlp.871
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
18413–18437
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.871/
DOI:
10.18653/2026.findings-emnlp.871
Bibkey:
Cite (ACL):
Guijia Zhang, Hao Zheng, and Harry Yang. 2026. Hallucination as Exploit: Evidence-Carrying Multimodal Agents. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 18413–18437, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Hallucination as Exploit: Evidence-Carrying Multimodal Agents (Zhang et al., Findings 2026)
Copy Citation:
PDF:
https://aclanthology.org/2026.findings-emnlp.871.pdf