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AI browsers indirect prompt injection via URL fragments HashJack security flaw

Vulnerability
First reported
Last updated
Happening score
H score 28
2 unique sources, 2 articles

Summary

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HashJack is an indirect prompt injection vulnerability in AI browsers that hides attacker instructions after the # symbol in legitimate URLs, letting a normal-looking link manipulate the assistant into unsafe actions. The issue affected Comet, Copilot for Edge, and Gemini for Chrome; by November 25, fixes had been applied to Comet and Copilot for Edge, while Gemini for Chrome remained unresolved. Researchers said the technique could enable callback phishing, data exfiltration, misinformation injection, malicious downloads, opening ports, and credential theft, and that ordinary server-side and network defenses do not see the fragment payload.

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Timeline

  1. 26.11.2025 12:15 2 articles · 7mo ago

    HashJack fixes applied to Comet and Copilot for Edge

    Mitigation Patch Update

    Perplexity and Microsoft had applied fixes for Comet and Copilot for Edge by November 25, while Gemini for Chrome remained unresolved for HashJack, the indirect prompt injection that hides malicious instructions in the text after the # symbol in legitimate URLs.

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  2. 26.11.2025 12:15 2 articles · 7mo ago

    Security researchers disclose HashJack indirect prompt injection

    Initial Disclosure

    Security researchers disclosed HashJack as a new indirect prompt injection vulnerability that tricks AI browsers such as Comet, Copilot for Edge and Gemini for Chrome by hiding malicious instructions in URL fragments after the # symbol. The technique can support callback phishing, data exfiltration, misinformation injection, malicious downloads, opening ports and credential theft, while traditional network and server defenses like intrusion detection systems do not see the fragment payload.

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