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Microsoft finally patches critical one-click Copilot vulnerability, almost eight months after learning of it
Almost eight months after confirming a critical security vulnerability within the personal version of its AI assistant, Copilot, Microsoft on Tuesday issued a patch to close the hole, which relies on an LLM’s inability to distinguish the data in a query from an instruction.
The CoSnitch hole was discovered by Varonis, and marked the third Copilot bug that Varonis has reported to Microsoft this year, following Reprompt, which bypassed Copilot guardrails by repeating queries, and SearchLeak, which Varonis said turned Microsoft 365 Copilot Enterprise into “a silent exfiltration tool. All three share the same exploit pattern: one click on a legitimate-looking link is enough.”
A detailed blog, posted by Varonis on Tuesday, said the hole’s capabilities were significant.
CoSnitch relied on an attacker leveraging three different Copilot flaws, Varonis wrote:
- Automatic prompt execution. “The ?q= URL parameter, combined with an undocumented parameter, causes any attacker-supplied prompt to execute instantly on page load: no click, no confirmation, no user action. One link is all it takes.”
- Data exfiltration to external servers. “An injected prompt can query the victim’s connected apps, such as Gmail, Drive, Calendar or OneDrive, encode the results into a URL and exfiltrate them via Copilot’s built-in URL-fetch capability to an attacker-controlled webhook.”
- Persistent memory poisoning via web summarization. “A crafted webpage, when summarized by Copilot, injects attacker instructions into the victim’s permanent memory store. The injection survives password changes, session revocation, and device re-enrollment, persisting forever.”
But the potentially most intriguing element of the CoSnitch bug was how it was discovered: Copilot essentially revealed the hole itself.
Copilot revealed its own flaw“We prompted Copilot to explain why auto-execution was impossible, and each refusal came with a technical justification, which mapped the architecture,” the Varonis post said. Varonis then “reframed every refusal as a follow-up question, and each answer narrowed the attack surface further. Copilot then disclosed an undocumented URL parameter, unprompted, mid-refusal, including its historical behavior and every protection put in place to disable it. We built the URL exactly as described. With no click or confirmation from the user, the prompt was successfully executed automatically. Copilot wasn’t breached; it was played.”
Microsoft confirmed both the flaw and the fix, emailing a statement that said, “our customers are already protected and do not need to take any action. We continuously update our guardrails to strengthen our protections against similar techniques.” It also issued an MSRC disclosure labeling the hole “critical.”
But Microsoft’s emailed comments also included a statement that is not strictly accurate: It said, “enterprise customers using Microsoft 365 Copilot are not affected.”
But analysts and others stressed that the complex nature of enterprise environments would often also house some consumer-grade Copilots from the personal accounts of workforce members, meaning that the flaw in the personal version could have absolutely impacted the enterprise version.
This is further complicated by the fact that Microsoft also said that it “is in the process of moving toward a more unified Copilot experience,” referred to as Copilot Fusion; details of the planned product merger began to leak last month. That means that enterprise CISOs need to be concerned about flaws in the personal version of Copilot that may be carried over into the merged offering.
The timing of Microsoft’s fix was also fragmented. Varonis reported the CoSnitch hole on December 31, and the company patched one element of the hole, its auto-execution capability, on February 1, noted Lior Adar, a Varonis senior security researcher, in an interview, but it didn’t complete the fix until Tuesday.
That February patch “lowered the other vulnerabilities significantly,” Adar said. And, added his colleague, Chen Levy Ben Aroy, the Varonis Cloud Security Research Team leader, “LLMs are a whole new world of vulnerabilities.”
Mark Tauschek, VP and distinguished analyst at Info-Tech Research Group, said that he found the Varonis methodology of tricking Copilot into revealing its own flaws powerful.
Varonis used “a very sophisticated combination of social engineering on an LLM, a variety of jailbreaks, and a prompt injection attack that is very concerning in its capability,” he said. “The combination of hack vectors is what makes it more startling, as we’ve seen all of those methods alone before, but I think all three working for one exploit is new, at least from a disclosure perspective.”
For CISOs, Tauschek said urgent action might be required.
“Much like in the old macro virus days in the late 90s and early 2000s, the only way to definitively stop it is to turn it off. Disable macros back then. Disable Copilot now,” Tauschek said. “There are many mitigation steps that can reduce risk to negligible, but that’s not zero. The point is, it’s just the beginning.”
The money trail will make this fix difficultAman Mahapatra, chief strategy officer for Tribeca Softtech, a New York City-based technology consulting firm, said there is a much more difficult issue involved in this case. He argued that the financial incentives for the major AI companies will make meaningfully fixing these kinds of holes almost impossible.
He pointed out that every guardrail that would fully close this class of attack degrades the product, because the same capabilities being exploited are the features that Microsoft is marketing as Copilot’s value. “The fix and the feature are in direct tension, which means these will not be cleanly patched so much as perpetually mitigated, and the eight-month window is what it looks like when a vendor is negotiating between its security obligation and its product roadmap on every single fix,” Mahapatra said.
“This is the pattern CISOs must internalize: in agentic systems, the malicious action and the legitimate action are the same action with different intent, which collapses the entire signature-and-anomaly detection model that enterprise security has been built on for twenty years,” Mahapatra said. “CoSnitch is serious, but its defining property is that nothing was broken. Three chained flaws: an autorun URL parameter firing a prompt with no click, OAuth connector abuse reading full Gmail bodies rather than metadata, and persistent memory poisoning through web summarization, and every one is Copilot doing exactly what it was designed to do.”
Mahapatra added that the third element of the CoSnitch flaw is the most troubling.
“The memory-poisoning component is the one being undersold, and it is the most dangerous. A single summarized webpage writes attacker instructions into Copilot’s persistent memory, and that memory survives password changes, session revocation, and device re-enrollment,” he said. “Every standard incident response step leaves the injection intact. The attacker needs no persistent infrastructure after the initial write, because every future session runs under attacker-controlled context, recorded only in a memory settings UI almost no user has opened.”
Flavio Villanustre, CISO for the LexisNexis Risk Solutions Group, also pointed to a bigger-picture issue that impacts all agentic and genAI deployments.
“The mechanisms behind the prompt injection part of the attack are based on the inability of the LLM to differentiate between data, the unsafe data stream coming from an external web page, and instructions which happen to be embedded in that data stream by the attacker controlling that external web page,” Villanustre said. “This is another example of why a different architectural approach to LLMs that separates data and instructions is needed to better guarantee the safety of their operation. This is not something that Microsoft or any other AI vendor has addressed to date.”
AI’s attribution problem gets worse as models scale
Diffusion models are becoming sophisticated enough that they can reproduce an image even when they don’t have access to the original.
In a series of ‘what if’ scenarios, researchers associated with MIT’s Computer Science & Artificial Intelligence Laboratory (CSAIL) swapped out different training datasets to test the impact on image outputs when original image data was completely removed.
It turns out that, at sufficient scale, nothing changed.
The researchers call the phenomenon “attribution decay”: The more data a diffusion model is trained on, and the larger it gets, the less individual inputs matter.
“If you take away a piece of data and the output of the model doesn’t change, then that piece of data didn’t affect the output,” Zheng Dai, lead author on the work, explained in an MIT blog post.
These findings could have significant ramifications when it comes to resolving growing concerns about intellectual property (IP) and copyright infringement.
Models can recreate images even if they’ve never ‘seen’ themModern generative diffusion models essentially replicate statistical patterns in large training datasets to create realistic reproductions. These powerful tools have achieved “remarkable results” in a wide array of applications, the researchers noted, notably image, video, and audio generation.
But they are increasingly under scrutiny by creatives, companies, and policymakers, who all want a way to assign responsibility for generated outputs. Models sit at the center of lawsuits, licensing deals, and proposed regulations around the world.
For instance, Stability AI (maker of Stable Diffusion) and Midjourney are embroiled in an ongoing class action lawsuit filed by several artists in federal court in California. The claimants argue that the popular image, video, and audio-creating models are scraping billions of their copyrighted images without their consent.
Getty Images also brought claims against Stability AI, but they were struck down by the High Court of Justice Business and Property Courts of England and Wales, although Getty did partly win trademark claims because some AI-generated images closely resembled its work.
Attributability, the MIT CSAIL researchers noted, would increase understanding of “machine unlearning,” data poisoning, model interoperability, fairness, and privacy, while also addressing ethical, legal, financial, and regulatory issues.
“Developing a method to attribute generated outputs to influential training data would greatly advance our understanding of and ability to regulate these models,” the researchers wrote.
In their experiments, they used ablation, which is essentially testing what happens when certain elements are removed by looking at what a model might have produced if it had never “seen” a particular image.
Typically, ablation is difficult because models need to be retrained after data is pulled out. But the MIT CSAIL researchers applied the method to a “diffusion ensemble” architecture of many different components trained on different pieces of data. These components could be swapped out to determine how much of an impact, if any, each one had.
“Our analysis is based on observing changes in model behavior, or lack thereof, upon omitting a part of the training set,” the researchers explained.
To do so, they trained 24 ensembles on datasets containing anywhere from 256 to 160,000-plus images. These were pulled from seven publicly accessible image datasets, including ArtBench (artwork), CIFAR-10 (generic colored images), Fashion-MNIST (clothing and accessories), CelebA (celebrity faces), and MetFaces (human faces).
In one example, they presented an image of a famous oil painting generated by a model trained on public domain artwork from 744 artists. It was shown side-by-side with hundreds of seemingly identical images that the model had generated, even when specific artists had been removed from training data.
The original was re-imagined in every possible variation, and the researchers quantified attributability by measuring the largest change they could induce by omitting training data. The radius became smaller as datasets became bigger, holding true across different measurements including pixel-by-pixel or semantic meaning.
In other words, single artworks by specific artists, or photographs of certain people, could be entirely removed from datasets, and the model could still reproduce that image or style. Essentially, tangible connections are lost, and linking to specific data points responsible for generated samples is “practically impossible,” or can even vanish, the researchers explained.
Their method is novel, they said, because prior work has focused on removing large swathes of data rather than targeting smaller pieces, what they called “leave-one-out style attribution.”
The impact on attributabilityBecause the experiment shows that, as Dai put it, it “doesn’t make much sense” to attribute a given output to a given piece of data, creatives and others may not be able to provide an audit trail tracing back to their original work.
Co-author David Gifford, an MIT professor and CSAIL principal investigator, said the findings have a direct bearing on legal questions around whether model outputs are actually derivative works.
“One way to think about this is that these models are creative,” he said. “They are not simply copying what they are fed, but creating brand new outputs.”
So if outputs can’t be correlated to individual pieces of training data, questions can be raised around fair use and whether, in fact, model-generated outputs are themselves copyrightable as “novel works,” Gifford said.
It could also shift the conversation about how original creators are compensated when what comes out of a model seems a direct recreation of their work, but can’t be traced back to anything on the internet.
Ultimately, producing outputs that are guaranteed to be unattributable is an “obligation for the industry, rather than a loophole,” he said. AI builders “need to revise their models to take advantage of the advances in this work, so they can show they’re not creating derivatives of individual people or items.”
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Google has paid $10 million in a bankruptcy auction for a large amount of data from the defunct Spirit Airlines, Bloomberg Law reports.
The purchase includes 100 million emails, 500 million messages, data from Microsoft Teams, as well as information on revenue, flight operations, marketing, personnel, and project management. The material also includes 30 million lines of program code, development data, and various software models and algorithms, as well as pricing data from 7.2 billion competing flights and approximately 7.5 billion passenger transactions.
No personal data will be included in the deal, and according to Google, a third party will review the material and remove any information that could identify individuals. Google said the data will then be used to improve the company’s products and AI models.
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Microsoft Copilot reveals secret input that allowed it to be hacked
It’s not every day that attackers can force a frontier AI model to cough up user passwords and other sensitive data without user confirmation. That’s exactly what researchers recently did to Microsoft 365 Copilot for enterprise. Even more unusual is the source they tapped to discover the critical vulnerability that made their exploit possible. Rather than employing reverse engineering or other traditional vulnerability-hunting methods, they asked Copilot. The LLM assistant readily complied.
Researchers at security firm Varonis knew they wanted to create an exploit that would exfiltrate user data when a user did nothing more than click on a link. Like most AI assistants today, Copilot steadfastly refused and made clear that sensitive prompts like that require explicit user consent in the form of a gesture, such as pressing a return key or other key. In response, the researchers peppered Copilot with questions about the guardrails that required user confirmation before the assistant could execute powerful commands.
Loose lips sink shipsThe dialog was like a game of 20 questions. Each answer provided a new clue that divulged information about the complex safety mechanism. Why was auto-execution impossible, they asked. What URL structures and deep links were involved? What happens when a page is loaded with input already in the prompt field? Each answer provided a deeper view into the guardrail and its limits. Eventually, Copilot provided a stunning Microsoft trade secret—an undocumented prompt parameter that completely bypassed the requirement for user consent.
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