REVIEW 3 major objections 5 minor 37 references
Con Instruction: Universal Jailbreaking of Multimodal Large Language Models via Non-Textual Modalities
T0 review · 3 major / 5 minor · reviewed 2026-08-07 · deepseek-v4-flash
Pith's one-line read The paper claims that a malicious instruction can be hidden entirely inside an image or audio clip by optimizing the non-textual input's embedding to match the instruction's text embedding in the fusion space, and that multimodal LLMs…
desk verdict A solid, well-evaluated jailbreak paper for MLLMs with a genuinely new audio result and a useful evaluation framework; the main soft spots are methodological details to tighten in revision. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The carrying mechanism is embedding-space alignment in the fusion layer. For a target instruction $\text{Inst}$, the attack computes $H_{\text{Inst}} = T(\text{Inst})$, the text token embeddings; initializes the adversarial sample $X_{\text{adv}}$ as Gaussian noise; and minimizes $L = D(H_{\text{Inst}}, H_{\text{adv}})$ with $H_{\text{adv}} = F(E(X_{\text{adv}}))$, where $E$ is the vision or audio encoder, $F$ is the multimodal fusion module, and $D$ combines L2 distance with cosine similarity. Optimization selects the last $N_{\text{inst}}$ visual or audio embeddings to match the $N_{\text{inst}}$ token embeddings, an empirical choice reported to give the best attack rate. The attack operates in a gray-box setting: it needs access to the encoder, the token-embedding layer, and the fusion module, but not the full language model.
What would settle it
Measure the embedding distance after optimization: if a large fraction of successful attacks have final distance above the preset threshold $\tau$, the attack's claimed mechanism (minimizing $D$ below $\tau$) is not doing the work.
Extended reading notes
Core claim
The central claim is that multimodal LLMs' joint embedding space can be used as a carrier for instructions: an adversarial image or audio snippet optimized to be close to a target text prompt in that space is sufficient to make the model produce harmful content, even when the text-only version of the instruction is refused. The authors show this with a two-stage attack: Stage I optimizes the non-textual sample under a combined Euclidean-plus-cosine distance between its fused embedding and the target instruction's token embeddings, using the last $N_{\text{inst}}$ embeddings of the image; Stage II pairs the sample with an empty string or benign helper texts (Agree, Anti, Hypo) that amplify recognition and success rates. They further claim that existing evaluation metrics such as refusal matching and StrongREJECT misclassify responses, and that their four-class ARC with an LLM judge agrees with human annotation at roughly 88%.
Load-bearing premise
The attack collapses if closeness in the fusion embedding space does not reliably make the language model decode the target instruction; if that fails, minimizing the distance would produce noise that is near the text instruction in embedding distance but semantically unreadable by the model.
Editorial extensions
If this is right
- If Con Instruction is correct, text-only safety filters are insufficient because harmful instructions can arrive entirely through images or audio.
- The same adversarial recipe works across vision and audio models, so the safety gap is not specific to one encoder or one modality.
- Pairing the non-textual sample with benign helper text such as Hypo amplifies attack success, showing that safety alignment is weaker for non-textual input than for equivalent text.
- Larger multimodal models can be more vulnerable than smaller ones to this attack, even when they are more robust to text-only jailbreaks.
- Existing defenses vary widely: MLLM-Protector and heavy input noise reduce success substantially, while self-assessment and VLGuard fine-tuning still leave nontrivial attack success rates.
Reading between the lines
- An implication left implicit is that the same embedding-alignment recipe could be adapted to black-box models by training a surrogate encoder and fusion module, in which case the gray-box requirement would become a practical rather than conceptual barrier.
- The paper's t-SNE observation that adversarial activations mix with safe queries suggests a detection hook: a defense could exploit activation geometry rather than response text, though no such defense is constructed here.
- The last-$N_{\text{inst}}$ embedding heuristic implies that token-position alignment matters; a testable extension would randomize which visual embeddings are matched to instruction tokens to see whether position is load-bearing for the attack's success.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes Con Instruction, a gray-box jailbreak attack against multimodal large language models (MLLMs). The method initializes an image or audio snippet from random noise and iteratively optimizes it so that its embeddings after the encoder and fusion module align with the token embeddings of a target malicious text instruction, using a combination of Euclidean distance and cosine similarity. The generated non-textual adversarial example, optionally paired with benign text prompts (Agree, Anti, Hypo), is shown to elicit harmful responses from LLaVA-1.5 (7B/13B), InternVL (13B/34B), Qwen-VL, and Qwen-Audio on AdvBench and SafeBench. The paper also introduces the Attack Response Categorization (ARC) framework with an LLM judge validated against human annotations (88% agreement), and evaluates several defense strategies.
Significance. If the results hold, this is a significant contribution to multimodal safety research. The attack demonstrates that non-textual modalities can carry arbitrary malicious instructions in a way that bypasses text-focused safety alignment, including audio, which previous OCR-based attacks do not cover. The ARC evaluation framework is a practical improvement over refusal-string matching and existing judge-based metrics. The paper releases code, includes human-validated evaluation, and reports extensive ablations across model families and modalities. These strengths make the empirical claims credible and the work likely to influence future defense research.
major comments (3)
- [Section 3.1, Algorithm 1] The central claim that minimizing the distance D(H_Inst, H_adv) in the fusion space makes the MLLM decode and obey the target instruction is not directly validated. The paper reports no distribution of final D values, no analysis of ASR versus D, and no control experiment in which the target instruction's text token embeddings are inserted directly at the non-textual token positions while the rest of the prompt is held fixed. Such a control would test whether the embedding space is semantically shared and whether the optimization is transferring instruction content rather than producing a generic safety-disabling perturbation. Without it, the observed high ASR could be partly attributable to optimization side effects (e.g., global perturbation of all visual tokens or position-specific cues) rather than faithful transfer of the instruction. This matters for the 'universal' claim across architectures. Please add (a) a control with direct embedding insertion, (b) reporting of final D values per model, and (c) an ASR-versus-D analysis.
- [Section 3.1 (distance function and threshold)] The distance function D is underspecified. The paper states that 'combining Euclidean distance and cosine similarity often yields better results' but does not provide the exact formula or the relative weights of the two terms. Table 4 shows qualitative improvement but no numerical definition. Because the stopping criterion in Algorithm 1 is L > tau, and tau is hand-tuned per model (0.60/0.75/0.85), the threshold is not scale-invariant and has no consistent semantic meaning across models. Please specify D exactly (including any normalization and weights), report the achieved final D values, and describe how tau was selected (e.g., the number of optimization steps or examples used for tuning).
- [Eq. (2), Table 3, Abstract] The success metric is the max over n=5 sampled responses (Eq. 2). The headline figures in the abstract (81.3% and 86.6% on LLaVA-v1.5 13B) correspond to this max-of-5 metric, not to a single response. While n=5 is disclosed in Section 4.1, the abstract and conclusions do not state this, which overstates the per-query attack reliability. Please report single-response ASR alongside the max-of-5 metric in Table 3 (or at least in an appendix table), and explicitly mention the max-of-5 definition in the abstract.
minor comments (5)
- [Section 4.2, Finding A1] The text mentions 'ESCO', but the method is called ECSO (Gou et al., 2025); please correct the acronym.
- [Section 3.1] The notation for the non-textual encoder is inconsistent: the text says 'I(·)' while Algorithm 1 uses 'E(·)'. Please unify the notation.
- [Appendix A] There are several typos: 'utlized' should be 'utilized', 'Guassian' should be 'Gaussian', and 'detecor' should be 'detector'.
- [Table 4] In the sentence preceding Table 4, 'additon' should be 'addition'.
- [Eq. (2)] The display of Equation (2) is malformed ('n max i=1'); it should be formatted as a proper max over i=1..n.
Circularity Check
No significant circularity: the attack success rate is measured externally by response quality, not by the embedding-distance objective, and no load-bearing claim reduces to a fitted parameter or self-citation.
full rationale
The paper's method optimizes an adversarial image or audio to minimize the distance D(H_Inst, H_adv) between its embedding and the target instruction's text-token embedding (Alg. 1). The claimed result, however, is the attack success rate defined in Eq. (2) as isSuccess(t) = max_i Eval(Inst^t_adv, r_i), where Eval is an external evaluation of the generated response (ARC, StrongREJECT, or refusal matching). Success is therefore not the same quantity as the optimized distance; it is an empirical outcome conditional on the model decoding and following the instruction. The paper reports text-only baselines, prior multimodal attacks, and ablations over the loss function (Table 4), so the contribution of the embedding-alignment step is separately identifiable rather than being forced by construction. The only fitted components are optimization hyperparameters such as the per-model threshold tau, which stop the optimization but do not define ASR. Self-citations (e.g., Geng et al. 2025, Li et al. 2025) appear in background or supporting analysis, not as load-bearing premises of the central attack claim, and no uniqueness theorem or prior-work-as-ansatz is invoked to forbid alternatives. The paper also acknowledges limitations about architecture generality and gray-box access, further indicating the claims are empirical rather than definitional. Thus, no circular step rises above the threshold for flagging.
Assumptions & free parameters
free parameters (3)
- threshold tau =
0.60 (LLaVA-7B, Qwen-VL, Qwen-Audio), 0.75 (LLaVA-13B, InternVL-13B), 0.85 (InternVL-34B)
- loss combination weights for Euclidean and cosine distance =
unspecified
- number of sampled responses n for max-based success =
5
assumptions (4)
- domain assumption Minimizing the distance between non-textual adversarial embeddings and target instruction token embeddings transfers the instruction's semantics to the image or audio such that the LLM follows it.
- domain assumption The attacker has gray-box access to the non-textual encoder, the language fusion module, and the token embedding layer of the victim model.
- domain assumption The GPT-4 judge using the ARC taxonomy assigns labels with sufficient accuracy (about 88% agreement with humans on a subset) to serve as the main evaluation metric.
- domain assumption Taking the maximum of five sampled responses is a valid definition of attack success.
Cite this review
Pith. "Pith review of Con Instruction: Universal Jailbreaking of Multimodal Large Language Models via Non-Textual Modalities." pith.science (2026). https://pith.science/paper/TIAMFFWU
@misc{pith2026250600548,
author = {Pith},
title = {Pith review of: Con Instruction: Universal Jailbreaking of Multimodal Large Language Models via Non-Textual Modalities},
year = {2026},
howpublished = {\url{https://pith.science/paper/TIAMFFWU}},
note = {Machine review of arXiv:2506.00548}
}
read the original abstract
Existing attacks against multimodal language models (MLLMs) primarily communicate instructions through text accompanied by adversarial images. In contrast, we exploit the capabilities of MLLMs to interpret non-textual instructions, specifically, adversarial images or audio generated by our novel method, Con Instruction. We optimize these adversarial examples to align closely with target instructions in the embedding space, revealing the detrimental implications of MLLMs' sophisticated understanding. Unlike prior work, our method does not require training data or preprocessing of textual instructions. While these non-textual adversarial examples can effectively bypass MLLM safety mechanisms, their combination with various text inputs substantially amplifies attack success. We further introduce a new Attack Response Categorization (ARC) framework, which evaluates both the quality of the model's response and its relevance to the malicious instructions. Experimental results demonstrate that Con Instruction effectively bypasses safety mechanisms in multiple vision- and audio-language models, including LLaVA-v1.5, InternVL, Qwen-VL, and Qwen-Audio, evaluated on two standard benchmarks: AdvBench and SafeBench. Specifically, our method achieves the highest attack success rates, reaching 81.3% and 86.6% on LLaVA-v1.5 (13B). On the defense side, we explore various countermeasures against our attacks and uncover a substantial performance gap among existing techniques. Our implementation is made publicly available.
Figures
Figures from the paper (3 more)
Reference graph
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Reviewed August 7, 2026 · model on record in the stance chip above.
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