Universal Jailbreak Suffixes Are Strong Attention Hijackers
Authors: name: Matan Ben-Tov; name: Mor Geva; name: Mahmood Sharif
Published: 2025-06-15 15:20:37

Abstract: We study suffix-based jailbreaksx2013a powerful family of attacks
against large language models (LLMs) that optimize adversarial suffixes to
circumvent safety alignment. Focusing on the widely used foundational GCG
attack (Zou et al., 2023), we observe that suffixes vary in efficacy: some
markedly more universalx2013generalizing to many unseen harmful
instructionsx2013than others. We first show that GCG's
effectiveness is driven by a shallow, critical mechanism, built on the
information flow from the adversarial suffix to the final chat template tokens
before generation. Quantifying the dominance of this mechanism during
generation, we find GCG irregularly and aggressively hijacks the
contextualization process. Crucially, we tie hijacking to the universality
phenomenon, with more universal suffixes being stronger hijackers.
Subsequently, we show that these insights have practical implications: GCG
universality can be efficiently enhanced (up to times5 in some cases) at no
additional computational cost, and can also be surgically mitigated, at least
halving attack success with minimal utility loss. We release our code and data
at http://github.com/matanbt/interp-jailbreak.