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When Actions Disappear: Adversarial Action Removal in Self-Play Reinforcement Learning

Summary

We study adversarial action masking in self-play reinforcement learning: an attacker selectively removes legal actions from a victim's action set. Experiments across poker and non-poker domains show learned masking causes more damage than random masking and perturbation baselines, persists across multiple RL algorithms, transfers across agents, is amplified by self-play, and shows no recovery under extended masked training.

SourcearXiv Machine LearningAuthor: Arahan Kujur
When Actions Disappear: Adversarial Action Removal in Self-Play Reinforcement Learning
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[2605.16312] When Actions Disappear: Adversarial Action Removal in Self-Play Reinforcement Learning

[Submitted on 4 May 2026]

Title:When Actions Disappear: Adversarial Action Removal in Self-Play Reinforcement Learning

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Abstract:We study adversarial action masking in self-play reinforcement learning: an attacker selectively removes legal actions from a victim's action set. Unlike observation or action perturbations, removal eliminates decision options before the agent acts. Across poker games scaling from 6 to 5,531 information states and two non-poker domains, learned masking causes substantially more damage than random masking and learned perturbation baselines. The attack persists across Q-learning, PPO, NFSP, neural NFSP, and DQN victims; transfers across agents; is amplified by self-play; and shows no recovery under extended masked training. Mechanistically, the adversary targets high-value decision points, captured by reach-weighted contingent action capacity (CAC$_w$) and a value-weighted refinement CAC$_v$. These results identify action availability as a distinct robustness surface in self-play RL.

Comments: 17 pages, 2 figures, 18 tables

Subjects:

Machine Learning (cs.LG); Artificial Intelligence (cs.AI)

ACM classes: I.2.6; I.2.11

Cite as: arXiv:2605.16312 [cs.LG]

(or arXiv:2605.16312v1 [cs.LG] for this version)

https://doi.org/10.48550/arXiv.2605.16312

arXiv-issued DOI via DataCite

Submission history

From: Arahan Kujur [view email] [v1] Mon, 4 May 2026 14:05:39 UTC (34 KB)

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Key points and analysis

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Key points

  • Attack removes legal actions rather than perturbing observations or actions, directly eliminating decision options.
  • Learned masking significantly outperforms random masking and perturbation baselines across various RL algorithms (Q-learning, PPO, NFSP, etc.).
  • Attack transfers across agents and is amplified by self-play, with no recovery under extended masked training.
  • Mechanistically, the attacker targets high-value decision points, captured by reach-weighted contingent action capacity (CAC_w) and a value-weighted refinement (CAC_v).

Highlights and analysis are generated automatically and may contain errors. Check the original source.