New Attack Targets Relational Geometry in Contrastive Embeddings.

Fei Zhao, Peiyuan Zhang, Xi Li, Chengcui Zhang, Nitesh Saxena· August 12, 2026 View original

Key takeaways

  • Contrastive embedding models are vulnerable to geometry-aware adversarial attacks.
  • Attacks can distort relational geometry by manipulating positive and negative pair distances.
  • A lightweight generator can enable real-time attacks after offline training.
  • Verification system performance can be severely degraded, with similarity structures reversed.

Who benefits

CybersecurityBFSIBiometricsAI DevelopmentDefense

Summary

This paper introduces a novel adversarial attack framework that targets the relational geometry of contrastive embedding manifolds, rather than traditional classification boundaries. The method systematically distorts similarity organization by pushing positive pairs apart and pulling negative pairs closer, significantly degrading verification system performance and reversing similarity structures.

A new adversarial attack framework has been developed to exploit vulnerabilities in contrastive learning and Siamese embedding models, which are foundational to modern verification systems. Unlike previous attacks that focused on discrete classification boundaries, this new approach, termed a geometry-aware adversarial attack, targets the relational geometry within the embedding space. It reformulates attacks as manifold-level relational corruption. The framework operates by systematically distorting the similarity organization of the embedding manifold. It achieves this by simultaneously pushing positive pairs of data points further apart while pulling negative pairs closer together, effectively collapsing and inverting the intended pairwise similarity structure. To make this scalable, the iterative optimization process is shifted offline to learn generalized geometry deformation patterns, allowing a lightweight generator to produce adversarial perturbations in a single forward pass. Experiments on various verification architectures, including Markmatch, demonstrated significant performance degradation, reducing accuracy from 95.4% to 38.6% and completely reversing the positive-negative similarity structure.

Why it matters

This research exposes a critical new vulnerability in contrastive learning systems, which are widely used for security and verification, necessitating a re-evaluation of their robustness and the development of new defense mechanisms.

How to implement this in your domain

  1. 1Re-evaluate the robustness of existing contrastive learning and Siamese embedding models against geometry-aware adversarial attacks.
  2. 2Develop and integrate new defense mechanisms specifically designed to protect the relational geometry of embedding manifolds.
  3. 3Implement continuous monitoring for anomalous similarity patterns in verification systems that could indicate a geometry attack.
  4. 4Investigate the use of adversarial training techniques tailored to defend against manifold-level relational corruption.

Original post by Fei Zhao, Peiyuan Zhang, Xi Li, Chengcui Zhang, Nitesh Saxena

"arXiv:2608.10237v1 Announce Type: new Abstract: Contrastive learning and Siamese embedding models have become the foundation of modern verification systems, where decisions are governed not by discrete classification boundaries, but by relational geometry in embedding space. Howe…"

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Originally posted by Fei Zhao, Peiyuan Zhang, Xi Li, Chengcui Zhang, Nitesh Saxena on X · view source

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