arxiv.orgpaper

Decoy Images Amplify Caption-Mediated Defenses Against Encoded Jailbreaks

Researchers report that attaching an unrelated "decoy" image to an encoded jailbreak prompt can sharply cut attack success rate against caption-mediated black-box VLM defenses like ECSO — up to 73 percentage points — even though the image itself is content-free, across five frontier VLMs, two encoded-attack families, and three defenses. Controls show the effect stems from image presence (not content or vendor filtering) and holds even under adaptive attacks targeting the caption re-check, but unconditional decoy attachment inflates benign refusal rates by 10–67pp, so the authors propose gating it on a lightweight encoded-input detector. The paper was withdrawn by the author after v2, so treat conclusions as unverified/retracted.