伪造推理过程可让思维链监控失效，暴露其脆弱性。
A False Average: Chain-of-Thought Monitors Collapse Where They Are the Only Defense
- 用伪造的合理推理替换原始推理，动作不变
- 监控捕获率从95%暴跌至11%以下
- 适用于多种模型和防御，适合研究安全漏洞者
思维链（CoT）监控旨在识别仅在推理中暴露的奖励劫持行为。我们发现，当攻击者控制推理过程时，该机制会完全失效。仅重写推理内容使其看似合理工程，而完整复制所有命令与输出，使攻击行为保持不变，即可在一次无梯度攻击中，将监控对特定子集的捕获率从约95%降至11%以下。监控的总体准确率是虚假平均：被那些行动中暴露的漏洞主导，掩盖了其在仅依赖思维链信号的场景下的近乎崩溃表现。该攻击在不同监控家族与代理模型间可迁移，且能在真实代理上复现；但针对校准后的监控规避，攻击主要集中于最强代理。仅基于轨迹的防御部分恢复效果，即便使用针对该攻击训练的模型也如此，因重写仍忠实记录事件，仅虚构意图；唯有外部信息能显著提升防御能力。对开源代理监控激活值的探测可分离出其误判的漏洞，但因果控制表明这只是检测器，非监控本身隐藏知识的证据。
原文摘要 · Abstract (English)
Chain-of-thought (CoT) monitoring is meant to catch the reward hacks that look clean in the actions and betray themselves only in the reasoning. We show that this is exactly where an adversary who controls the reasoning can defeat it. Rewriting only an agent's reasoning to read as good-faith engineering, while copying every command and output verbatim so the exploit is unchanged, drops a held-out monitor's catch rate on that subset from about 95% to under 11% in one gradient-free shot. A monitor's aggregate accuracy is a false average: dominated by hacks the actions give away, it hides the near-total collapse this rewrite produces on the subset where CoT monitoring is the only signal. The attack transfers across monitor families and agent models, reproduces with live agents, though against a calibrated monitor evasion concentrates in the strongest agent. Trace-only defenses recover it only partially, even one primed on the attack, because the rewrite stays truthful about what happened and lies only about intent; only information from outside the trace helps substantially. A probe on an open-weight surrogate monitor's activations separates the hacks its verdict misses, but a causal control shows this is a detector, not evidence the monitor secretly knows.
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