MS 워드 카피일럿을 통해 스스로 퍼지는 AI 웜 발견

Context Collapse, Part 3 - AI Worming through Word Contents Context Collapse, Part 3 - AI Worming through Word I would like to thank Microsoft product teams and Microsoft Security Response Center (MSRC) for collaborating with me on this technical analysis and mitigation of the disclosed vulnerabilities. The editorial opinions reflected below are solely the author’s and do not necessarily reflect those of the organizations I collaborated with. Summary The findings described in this post are part of a coordinated disclosure with MSRC and Microsoft product teams. Microsoft was provided with reproduction steps, videos, environmental assumptions, and the exact proof-of-concept (PoC) prompts used during testing. They were also informed of a 90-day coordination period before disclosure. This was extended two times, resulting a 144-day coordination period. In parts 1 and 2 in this series, I have shown how external inputs could influence Copilot responses and, in some cases, potentially lead to confidentiality impacts through Cross-Domain Prompt Injection Attacks (XPIAs) . This report builds on those findings and extends the XPIA analysis from single-interaction compromise to propagation across trusted document workflows. It shows that attacker-controlled instructions in one document can be copied into Copilot-generated or Copilot-edited Word documents, causing those downstream documents to become new carriers of the same attack. Previous examples of AI-worms exist. Notably, Morris II demonstrated self-replicating prompt propagation in GenAI-powered email-assistant ecosystems. However, to my knowledge, this is among the first public demonstrations of document-borne AI-worm self-propagation through normal workflows in a mainstream commercial productivity suite. The reported scenario is: Malicious instructions hidden in an externally shared document could make Copilot alter drafted or edited documents in Word and propagate the attack to new documents. The full attack in brief The attack An attacker places hidden instructions in a document that is later used as source material in Copilot for Word. Copilot may interpret those instructions as part of the user’s request, causing it to manipulate the document being drafted or edited. Copilot may then also copy the hidden instructions into the resulting document, turning that document into a new carrier. If the carrier is subsequently used in another Copilot-assisted workflow, the instructions can trigger again and propagate into further documents, even without the attacker’s original document being present. Example Consider an employee preparing a financial report. The employee downloads a market analysis from a trusted website that has been compromised, unaware that the document contains hidden instructions. The employee then includes the analysis as source material when drafting the report with Copilot. The hidden instructions cause Copilot to alter internal figures in the financial report and copy the attack into the new document. The employee saves and shares the apparently legitimate report internally. Later, a colleague uses it as source material for another report; the instructions trigger again, alter the new report, and copy themselves forward. The attack can therefore continue without further involvement from either the compromised website or the original malicious document. As affected reports are reused, additional reports and documents can become carriers of the attack. Disclosure status at publication Vendor: Microsoft Coordinated disclosure: Handled through MSRC and Microsoft product teams Included in this post: XPIA and self-propagation scenario in Microsoft Copilot for Word Customer action: No customer-side remediation fully addresses the issue at the time of publication. Customers can reduce exposure by: Treating externally sourced documents as untrusted when used with Copilot. Reviewing any attached document before starting a Copilot generation or edit. Carefully reviewing Copilot-generated or Copilot-edited documents before reusing, sharing, or distributing them. Microsoft-side status: Testing has reproduced the attack with all current mitigations deployed. At the time of publication, no robust mitigation for the broader vulnerability class is available. A note on disclosing before a fix Unlike Parts 1 and 2, this scenario remains exploitable at publication. I have weighed that carefully. The coordination period agreed with Microsoft has been exhausted, and testing shows that no robust mitigation for the broader vulnerability class is currently available. Two mitigation attempts, including a model upgrade, did not close the class. I have therefore chosen to disclose at the class level rather than the payload level. My reasoning is that defenders cannot reduce exposure to a risk they are unaware of, and the propagation mechanism described here affects ordinary document workflows that many organizations already rely on. Withholding the existence of the issue would leave those organizations unable to make an informed decision, while providing no additional protection. Disclosure timeline 2026-03-06 : Initial report submitted to MSRC with reproduction steps, videos, environmental assumptions, and PoC prompts. 2026-03-09 : MSRC acknowledged receipt and opened a case. 2026-03-31 : Microsoft confirms the reported behavior. 2026-03-31 : Microsoft product teams began mitigation work; ongoing technical discussion. 2026-04-03 : First mitigation go-live (The new “Edit with Copilot” experience) 2026-04-09 : Original attack prompt wording verified mitigated with “Edit with Copilot”. 2026-04-09 : Attack behavior reproduced in “Edit with Copilot” using a new XPIA prompt task (manipulating financials). Reported as separate case to MSRC. 2026-04-10 : MSRC acknowledged receipt and opened a case. 2026-04-10 : Microsoft product teams began mitigation work; ongoing technical discussion. 2026-06-08 : At Microsoft’s request, public disclosure was moved to 2026-07-15. 2026-07-14 : Second mitigation fix go-live. This mitigation consisted of upgrading the underlying model to GPT-5.5. 2026-07-15 : Successful exploit with worming reproduced using GPT-5.6, the latest available model at the time. 2026-07-15 : I suggest we postpone disclosure a further two weeks to 2026-07-28, to allow time for a new mitigation. 2026-07-15 : Microsoft agreed. 2026-07-28 : Attack still reproduces. 2026-07-28 : Coordinated public disclosure (this post). Threat model The attacker does not need access to the victim’s Microsoft 365 tenant. The attacker only needs to share a malicious document with the victim. This can be done through SharePoint, Teams, Outlook or any other way of sharing documents. Security boundary and observed behavior The relevant security boundary in this scenario is the boundary between attached documents and the current drafting document. If any of the attached documents contain an XPIA the attack may trigger. Copilot must read every attached document to determine which parts to include in its current drafting task. However, attached documents should be treated as untrusted information, not trusted user instruction. Boundary violation Attacker-controlled documents are downloaded or shared through email/sharepoint/other sharing option. If such documents are attached to Copilot during a drafting task, trust is broken. Expected behavior When a user asks Copilot to draft e.g. a Q1 financial report based on attached documents, Copilot should utilize the information in the attached documents without treating instructions embedded within documents as authoritative instructions. Observed behavior Instructions embedded in documents cause Copilot to alter its behavior. Here presented as: 1: Copilot silently changing numerical values in financial reports 2: Copilot propagating the full XPIA by pasting into downstream documents, which may then be used as attachments in later drafting sessions\ Crossing the trust boundary in Word The ini