~/talk

EmbedX: Embedding-Based Cross-Trigger Backdoor Attack Against Large Language

Talkat USENIX Security '25 · 2025-08-13..08-15· [security, large-language-models]
name:Nan Yan
links:none on file
name:Yuqing Li
links:none on file
links:none on file
name:Jing Chen
github:lancejchen
name:Kun He
links:none on file
name:Bo Li
links:none on file
slides:none on file

Introduces an embedding-space soft trigger that maps many tokens to one optimized continuous vector, injects it by freezing model weights and fine-tuning only the trigger, and enforces dual constraints in frequency and gradient to keep poisoned latents indistinguishable from clean ones. Evaluated on four open-source LLMs for classification and generation, EmbedX reaches ~100% attack success, switches triggers in 0.53 s, uses 5% poisoning and 1% false-trigger rate while preserving or even improving utility (~+3.2% accuracy); common defenses only partially reduce effectiveness.

AI-written summary · about

  1. 0:00Introduction
  2. 2:02Single-trigger limits
  3. 3:07Threat model goals
  4. 3:50EmbedX framework
  5. 4:55Latent vector injection
  6. 6:00Multi-token fuses
  7. 7:31Evaluation setup
  8. 9:18Performance results
  9. 10:23Cross-lingual attacks
  10. 11:33Fine-tuning robustness
  11. 12:37Defense evaluation
  12. 14:45Limitations future work
  13. 15:09Conclusion
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