Grok exfiltrates user data when malicious instructions are encrypted

Researchers at security firm Adversa devised an attack that tricks Grok, the AI assistant developed by Elon Musk's xAI, into exfiltrating user chats and personal data by encrypting malicious instructions, bypassing existing guardrails. The attack, disclosed to xAI in June, remained effective as of publication, highlighting the inability of large language models to fully prevent prompt injection vulnerabilities.

Earlier this week, researchers outlined an attack that used a secret input provided by Microsoft 365 Copilot for enterprise to cause the AI assistant to exfiltrate a password present in the user’s inbox. Now, a separate team has devised a similar attack against Grok. The new data theft hack employs a deceptively simple trick to force the Elon Musk-owned LLM to steal user chats and other personal information. At the time this post went live, the assistant continued to cough up the data, despite xAI being informed of it in June. The lesson from both this week’s episodes—and the countless other ones that have come before it—is that LLMs are incapable of solving the root causes for prompt injections, the most severe vulnerability classes they’re most prone to. That leaves AI developers with no other option but to build a guardrail that steers the model away from the harmful actions. As I noted in Tuesday’s story https://arstechnica.com/security/2026/08/microsoft-copilot-reveals-secret-input-that-allowed-it-to-be-hacked/ , the approach is tantamount to a road traffic safety engineer erecting a protective rail around a dangerous bend rather than banking the curve. Cryptographic Context Injection in the house Prompt injections exploit LLMs’ training to comply with user requests whenever possible. Attackers can capitalize on the predilection by smuggling harmful instructions into emails or webpages the assistant is instructed to summarize. Because LLMs can’t reliably distinguish between content in an email sent by an untrusted party and user instructions entered directly into a prompt, the overly solicitous LLM faithfully follows them. To date, Grok and other LLMs’ only recourse is to create guardrails that flag suspicious instructions and forbid them from being executed. Rony Utevsky, a researcher at security firm Adversa, recently discovered a simple way to completely bypass that restriction. Rather than composing the harmful instruction in plaintext, the hacker encrypts it. The website hosting the ciphertext also includes plaintext instructions for decrypting the encrypted content, along with the decryption key. Using this simple sequence, Grok then follows the command as soon as the user instructs the assistant to summarize the page. There is no warning, and no confirmation is required.