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Encrypted Prompts Defeat Grok and Gemini Guardrails; Chat Histories Stolen
Researchers at Adversa AI disclosed an attack technique that smuggles malicious instructions past AI safety filters by encrypting them. They then demonstrated it against production deployments of xAI's Grok and Google's Gemini - including a zero-click chain that could exfiltrate a Grok user's entire chat history.
The technique, which the researchers call Cryptographic Context Injection, inverts the usual assumption behind input filtering. Guardrails inspect prompts and retrieved content as text; an AES-256-GCM ciphertext contains no readable instruction to flag. The model itself performs the decryption inside its own code-execution sandbox, and then treats the recovered plaintext as trusted intermediate output rather than as untrusted external content. Adversa noted that every element a scanner would need is present on the page, but recovering it requires "running PBKDF2 and AES-256-GCM."
That distinction separates the work from earlier cipher-based jailbreaks such as CipherChat and CodeChameleon, which relied on substitution ciphers or Base64 encoding that large language models can decode natively during inference. Strong authenticated encryption forces execution, and execution is what launders the payload's provenance.
The demonstrated impact differed by target. Against Grok, the researchers showed an indirect, zero-click path. Encrypted JSON embedded in a web page is picked up when Grok's agentic browsing analyzes the site, and the decrypted instructions then leak session data like user name, coarse location, subscription tier and full conversation history, to an attacker-controlled URL. No click or warning reached the user.
Also read: French Police Raid X Offices as Grok Investigations Grow
Against Gemini 3 Flash on the web at the paid tier, the same approach produced instructions for building incendiary devices in the model's Deep Thinking mode, and caused the model to reproduce its own system instructions. Adversa said its Gemini success rate had fallen sharply since June and dropped significantly by August, but could not attribute the change to filter updates, model version changes or both.
Vendor engagement was limited. Adversa reported the Grok issue to xAI on June 3, received an initial acknowledgment, and followed up on August 4 and 10 without substantive response. The firm confirmed the attack still reproduced on August 19.
The Gemini finding was never formally reported, because Google's AI vulnerability reward program excludes prompt injection, jailbreaks and alignment issues from scope, directing them instead to in-product feedback channels. Guardrail-bypass research at one of the largest model providers therefore sits outside a coordinated-disclosure track with a reward and a disclosure clock.
The findings land against a body of evidence that prompt injection remains the dominant failure mode in deployed agentic systems, a position reflected in OWASP's guidance and in Microsoft research published in May on remote code execution in AI agent frameworks. The pattern here is narrower and more concerning for defenders. Content-based guardrails, the primary control most enterprises have deployed, are structurally unable to inspect a payload that only exists in plaintext after the model has already decided to trust it.
Whether xAI ships a fix or acknowledges the report, whether Google revises its reward-program scope to cover guardrail bypasses, and whether AI security vendors move detection from input text to sandbox execution monitoring, is something to watch-out for.
