Hidden Killer: Invisible Textual Backdoor Attacks with Syntactic Trigger

Fanchao Qi, Mukai Li, Yangyi Chen, Zhengyan Zhang, Zhiyuan Liu, Yasheng Wang, Maosong Sun


Abstract
Backdoor attacks are a kind of insidious security threat against machine learning models. After being injected with a backdoor in training, the victim model will produce adversary-specified outputs on the inputs embedded with predesigned triggers but behave properly on normal inputs during inference. As a sort of emergent attack, backdoor attacks in natural language processing (NLP) are investigated insufficiently. As far as we know, almost all existing textual backdoor attack methods insert additional contents into normal samples as triggers, which causes the trigger-embedded samples to be detected and the backdoor attacks to be blocked without much effort. In this paper, we propose to use the syntactic structure as the trigger in textual backdoor attacks. We conduct extensive experiments to demonstrate that the syntactic trigger-based attack method can achieve comparable attack performance (almost 100% success rate) to the insertion-based methods but possesses much higher invisibility and stronger resistance to defenses. These results also reveal the significant insidiousness and harmfulness of textual backdoor attacks. All the code and data of this paper can be obtained at https://github.com/thunlp/HiddenKiller.
Anthology ID:
2021.acl-long.37
Volume:
Proceedings of the 59th Annual Meeting of the Association for Computational Linguistics and the 11th International Joint Conference on Natural Language Processing (Volume 1: Long Papers)
Month:
August
Year:
2021
Address:
Online
Venues:
ACL | IJCNLP
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
443–453
Language:
URL:
https://aclanthology.org/2021.acl-long.37
DOI:
10.18653/v1/2021.acl-long.37
Bibkey:
Cite (ACL):
Fanchao Qi, Mukai Li, Yangyi Chen, Zhengyan Zhang, Zhiyuan Liu, Yasheng Wang, and Maosong Sun. 2021. Hidden Killer: Invisible Textual Backdoor Attacks with Syntactic Trigger. In Proceedings of the 59th Annual Meeting of the Association for Computational Linguistics and the 11th International Joint Conference on Natural Language Processing (Volume 1: Long Papers), pages 443–453, Online. Association for Computational Linguistics.
Cite (Informal):
Hidden Killer: Invisible Textual Backdoor Attacks with Syntactic Trigger (Qi et al., ACL 2021)
Copy Citation:
PDF:
https://aclanthology.org/2021.acl-long.37.pdf
Video:
 https://aclanthology.org/2021.acl-long.37.mp4
Code
 thunlp/HiddenKiller +  additional community code
Data
OLIDSST