SIGNALAI·May 27, 2026, 4:00 AMSignal75Medium term

Cordyceps: Covert Control Attacks on LLMs via Data Poisoning

Source: arXiv cs.LG

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Cordyceps: Covert Control Attacks on LLMs via Data Poisoning

arXiv:2605.26595v1 Announce Type: cross Abstract: Large language models (LLMs) are often fine-tuned on uncurated text datasets that adversaries can poison. Existing poisoning attacks primarily rely on fixed trigger phrases that defenses such as outlier detection, clean-data regularization, or online monitoring can neutralize. In this paper, we propose a data poisoning method that teaches an LLM an information hiding scheme reliably and stealthily through semantic associations between shared knowledge such as facts or concepts and attacker-chosen phrases. The induced hiding scheme can encode an

Why this matters
Why now

The proliferation of LLMs and their fine-tuning on less curated datasets creates new attack surfaces, making covert poisoning methods increasingly relevant.

Why it’s important

This research reveals a sophisticated new vector for adversarial control over LLMs, undermining trust and potentially enabling widespread disinformation or malicious instruction embedding.

What changes

Adversaries can now embed covert control mechanisms in LLMs via data poisoning, circumventing existing defenses that rely on detecting explicit trigger phrases.

Winners
  • · Threat intelligence firms
  • · Cybersecurity researchers
  • · AI red teamers
Losers
  • · LLM developers
  • · Organizations relying on unverified LLMs
  • · Users of poisoned LLMs
  • · Data providers
Second-order effects
Direct

Increased scrutiny and investment in supply chain security for LLM training data will become paramount.

Second

New regulatory frameworks may emerge to mandate transparency and auditability of LLM training datasets and methodologies.

Third

A 'trust deficit' in public-facing or critical LLM applications could grow, potentially slowing AI adoption in sensitive sectors.

Editorial confidence: 85 / 100 · Structural impact: 65 / 100
Original report

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Read at arXiv cs.LG
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