A researcher has discovered a weakness called PhantomRPC that Microsoft does not consider a vulnerability it plans to patch.

PhantomRPC involves Windows Remote Procedure Call (RPC), the core of communication between Windows processes. The vulnerability lets a process with impersonation rights escalate to SYSTEM by impersonating high‑privileged clients that connect to a fake RPC server.

The researcher presented a detailed technical report outlining five exploitation paths, including coercion, user interaction, or background services. They warned that potential vectors are “effectively unlimited” because the root issue is architectural.

Microsoft, however, classified the issue as “moderate,” refused a bounty, declined to assign a CVE (a spot in the list of Common Vulnerabilities and Exposures), and closed the case without tracking. Its position is that the technique requires an already‑compromised machine and does not provide unauthenticated or remote access.

Experts disagreed with Microsoft’s assessment. Their concern is that Microsoft is downplaying a systemic local privilege escalation technique that exists in all supported Windows versions.

The issue

At the core of this issue is that the Windows RPC runtime does not sufficiently verify that the server a high‑privileged client connects to is the intended legitimate endpoint.

If a legitimate RPC server is not reachable (for example because the service stopped, was misconfigured, not installed, or due to a race condition), an attacker with SeImpersonatePrivilege can spin up a fake RPC server that “fills the gap” using the same interface and endpoint.

When a SYSTEM or high‑privileged client connects to this fake server, using an impersonation level that allows the server to impersonate the client, the attacker can call RpcImpersonateClient and immediately escalate their privileges to SYSTEM.

From Microsoft’s perspective, the ability to run a rogue RPC server in this way falls under the category of “already compromised.”

SeImpersonatePrivilege

To understand the issue better, we need to dig into what SeImpersonatePrivilege does.

Basically, SeImpersonatePrivilege is the Windows permission that lets a program “pretend to be you” after you’ve already logged in, so it can do things on your behalf using your level of access.

It’s needed because many system services and server‑type apps (file sharing, RPC servers, COM servers, web apps) have to perform actions on behalf of a user, like reading their files or applying group policy.

If an attacker gains this privilege, they can create a fake service or server and wait for a more powerful account to talk to it. When that high‑privilege service connects, the attacker can grab its security token and impersonate it, effectively upgrading from an account with lower privileges to full SYSTEM control on that machine.

Protection

A Microsoft spokesperson provided the following statement:

“This technique requires an already-compromised machine and does not grant unauthenticated or remote access. Any update is a balance between existing compatibility and customer risk, and we remain committed to continually hardening our products. We recommend customers follow security best practices, including limiting administrative privileges and applying the principle of least privilege.”

In our opinion, mitigating PhantomRPC properly would require deep changes to the RPC architecture, which is hard to do on existing Windows versions without breaking compatibility. It’s maybe something we’ll see in future versions, given the scale of change needed.

What you can do:

• As PhantomRPC is a piece in a larger chain, it is still very important to keep Windows updated.
• Use your admin account sparingly and only for the tasks that need that kind of privilege.
• Use an up-to-date, real-time anti-malware solution that can detect and block suspicious privilege‑escalation activity.
• Avoid disabling or “hardening” services blindly since a malicious service might step in their place.

To answer the question in the title: it looks like a “feature” that can be abused in many ways; one that has outlived its original threat model. Defenders have to treat them as ongoing risks, rather than one‑off CVEs.

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Security researcher Alexander Hanff wrote an article titled Anthropic secretly installs spyware when you install Claude Desktop.

Claims like that are bound to create two sides, so we searched for an official rebuttal by Anthropic. But we couldn’t find one. It would surprise me very much if they’d be unaware of the claim, since there’s been some noise about it.

Users on Mastodon, Reddit, and LinkedIn are confirming the researcher’s findings and discussing the subject, so it’s hard to imagine Anthropic missed it.

Let’s look at the claims first.

While looking into another matter, the researcher discovered a Native Messaging host manifest on his Mac that he did not knowingly install. On Chrome and other Chromium-based browsers, extensions can exchange messages with native applications if they register a native messaging host that can communicate with the extension. 

By testing on a clean machine, Hanff discovered that Installing Claude Desktop for macOS drops a Native Messaging host manifest into multiple Chromium profiles (Chrome, Edge, Brave, Arc, Vivaldi, Opera, Chromium), even including for browsers that are not actually installed yet.

The Native Messaging host manifest tells a Chromium‑based browser which local executable to invoke when an extension calls a native host, and those hosts run outside the browser sandbox with current users  permissions. Hanff therefore describes this as a “backdoor.” The manifest pre‑authorizes three Chrome extension IDs, so any extension with those IDs can call the helper via connectNative, giving it access to browser automation features.

Another objection is that Claude makes simple deletion futile since the manifest will be recreated the next time the user launches Claude Desktop.

It’s important here to point out that his article is about Claude Desktop, the Electron-based macOS application with bundle identifier com.anthropic.claudefordesktop, distributed as Claude.app. It is not about Claude Code, Anthropic’s command line developer tool. Claude Code is autonomous (“agentic”), allowing you to hand over a task, and it handles the planning and execution until done. So, for Claude Code, it would absolutely make sense to enable communication with browsers, provided they are present on the target system.

So, we have an application that writes into other apps’ profile/support directories (the browsers’ configuration area) and can act as the user, with capabilities like using the logged‑in browser session, DOM inspection, data extraction, form filling, and session recording. This expands the attack surface of every machine this manifest is dropped on, without asking for consent. 

Anthropic’s own launch blog on “Claude for Chrome,” which discusses Anthropic’s internal red‑team experiments, explicitly mentions prompt injection as a key risk and reports attack success rates of 23.6% (no mitigations) and 11.2% (with mitigations). Hanff cites this to argue that a pre‑positioned bridge is a non‑trivial risk.

How bad is it?

Native Messaging is a standard Chromium mechanism. Nothing here is an unknown or exotic technique per se. Chrome’s own documentation explains that Native Messaging hosts run at user privilege and are invoked by browser extensions through a manifest file. And as the researcher pointed out, the bridge does nothing. But it could potentially be abused.

I don’t think it’s fair to say that Claude Desktop installs spyware, but it does open a system up by expanding the attack surface.

Anthropic already had a separate, documented Native Messaging manifest for Claude Code that users sometimes manually copied into other Chromium browsers; the new behavior is that Claude Desktop now drops a Claude‑Desktop‑related manifest into multiple browser paths automatically.

It requires a combination of extension and host. Only combined with a matching browser extension, this bridge enables the user-like capabilities we listed earlier.

What we don’t know yet

Anthropic hasn’t published a detailed technical privacy spec for the Claude Desktop–browser bridge, so we don’t know exactly what data flows when the Chrome integration is used, beyond the general capabilities described in their documentation (session access, DOM reading, etc.).

The detailed analysis and most replication so far are on macOS. We’re in the dark about behavior on Windows and Linux, and the same is true across different browser install paths. That behavior has also not been comprehensively documented in public write‑ups.

I did reach out to Anthropic asking for a response. If and when we get an official response from Anthropic, I’ll add it here, so stay tuned.

Conclusion

Anthropic likely wanted “Claude in Chrome”‑style capabilities across Chromium‑based browsers, but that doesn’t excuse doing it silently and preinstalling the manifest into profile directories for multiple browsers, including ones that are not yet installed.

There are better ways to implement changes like these, and users should at least be made aware of them so they can weigh the advantages against the potential risks.

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This blog is part of a series where we highlight new or fast-evolving threats in consumer security. This one focuses on how AI is being used to design more realistic campaigns, accelerate social engineering, and how AI agents can be used to target individuals.

Most cybercriminals stick with what works. But once a new method proves effective, it spreads quickly—and new trends and types of campaigns follow.

In 2025, the rapid development of Artificial Intelligence (AI) and its use in cybercrime went hand in hand. In general, AI allows criminals to improve the scale, speed, and personalization of social engineering through realistic text, voice, and video. Victims face not only financial loss, but erosion of trust in digital communication and institutions.

Social engineering

Voice cloning

One of the main areas where AI improved was in the area of voice-cloning, which was immediately picked up by scammers. In the past, they would mostly stick to impersonating friends and relatives. In 2025, they went as far as impersonating senior US officials. The targets were predominantly current or former US federal or state government officials and their contacts.

In the course of these campaigns, cybercriminals used test messages as well as AI-generated voice messages. At the same time, they did not abandon the distressed-family angle. A woman in Florida was tricked into handing over thousands of dollars to a scammer after her daughter’s voice was AI-cloned and used in a scam.

AI agents

Agentic AI is the term used for individualized AI agents designed to carry out tasks autonomously. One such task could be to search for publicly available or stolen information about an individual and use that information to compose a very convincing phishing lure.

These agents could also be used to extort victims by matching stolen data with publicly known email addresses or social media accounts, composing messages and sustaining conversations with people who believe a human attacker has direct access to their Social Security number, physical address, credit card details, and more.

Another use we see frequently is AI-assisted vulnerability discovery. These tools are in use by both attackers and defenders. For example, Google uses a project called Big Sleep, which has found several vulnerabilities in the Chrome browser.

Social media

As mentioned in the section on AI agents, combining data posted on social media with data stolen during breaches is a common tactic. Such freely provided data is also a rich harvesting ground for romance scams, sextortion, and holiday scams.

Social media platforms are also widely used to peddle fake products, AI generated disinformation, dangerous goods,  and drop-shipped goods.

Prompt injection

And then there are the vulnerabilities in public AI platforms such as ChatGPT, Perplexity, Claude, and many others. Researchers and criminals alike are still exploring ways to bypass the safeguards intended to limit misuse.

Prompt injection is the general term for when someone inserts carefully crafted input, in the form of an ordinary conversation or data, to nudge or force an AI into doing something it wasn’t meant to do.

Malware campaigns

In some cases, attackers have used AI platforms to write and spread malware. Researchers have documented campaign where attackers leveraged Claude AI to automate the entire attack lifecycle, from initial system compromise through to ransom note generation, targeting sectors such as government, healthcare, and emergency services.

Since early 2024, OpenAI says it has disrupted more than 20 campaigns around the world that attempted to abuse its AI platform for criminal operations and deceptive campaigns.

Looking ahead

AI is amplifying the capabilities of both defenders and attackers. Security teams can use it to automate detection, spot patterns faster, and scale protection. Cybercriminals, meanwhile, are using it to sharpen social engineering, discover vulnerabilities more quickly, and build end-to-end campaigns with minimal effort.

Looking toward 2026, the biggest shift may not be technical but psychological. As AI-generated content becomes harder to distinguish from the real thing, verifying voices, messages, and identities will matter more than ever.

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This blog is part of a series highlighting new and concerning trends we noticed over the last year. Trends matter because they almost always provide a good indication of what’s coming next.

If there’s one thing that became very clear in 2025, it’s that malware is no longer focused on Windows alone. We’ve seen some major developments, especially in campaigns targeting Android and macOS. Unfortunately, many people still don’t realize that protecting smartphones, tablets, and other connected devices is just as essential as securing their laptops.

Android

Banking Trojans on Android are not new, but their level of sophistication continues to rise. These threats continue to be a major problem in 2025, often disguising themselves as fake apps to steal credentials or stealthily take over devices. A recent wave of advanced banking Trojans, such as Herodotus, can mimic human typing behaviors to evade detection, highlighting just how refined these attacks have become. Android malware also includes adware that aggressively pushes intrusive ads through free apps, degrading both the user experience and overall security.

Several Trojans were found to use overlays, which are fake login screens appearing on top of real banking and cryptocurrency apps. They can read what’s on the screen, so when someone enters their username and password, the malware steals them.

macOS

One of the most notable developments for Mac users was the expansion of the notorious ClickFix campaign to macOS. Early in 2025, I described how criminals used fake CAPTCHA sites and a clipboard hijacker to provide instructions that led visitors ro infect their own machines with the Lumma infostealer.

ClickFix is the name researchers have since given to this type of campaign, where users are tricked into running malicious commands themselves. On macOS, this technique is being used to distribute both AMOS stealers and the Rhadamanthys infostealer.

Cross-platform

Malware developers increasingly use cross-platform languages such as Rust and Go to create malware that can run on Windows, macOS, Linux, mobile, and even Internet of Things (IoT) devices. This enables flexible targeting and expands the number of potential victims. Malware-as-a-Service (MaaS) models are on the rise, offering these tools for rent or purchase on underground markets, further professionalizing malware development and distribution.

Social engineering

iPhone users have been found to be more prone to scams and less conscious about mobile security than Android owners. That brings us to the first line of defense, which has nothing to do with the device or operating system you use: education.

Social engineering exploits human behavior, and knowing what to look out for makes you far less likely to fall for a scam.

Fake apps that turn out to be malware, malicious apps in the Play Store, sextortion, and costly romance scams all prey on basic human emotions. They either go straight for the money or deliver Trojan droppers as the first step toward infecting a device.

We’ve also seen consistent growth in Remote Access Trojan (RAT) activity, often used as an initial infection method. There’s also been a rise in finance-focused attacks, including cryptocurrency and banking-related targets, alongside widespread stealer malware driving data breaches.

What does this mean for 2026?

Taken together, these trends point to a clear shift. Cybercriminals are increasingly focusing on operating systems beyond Windows, combining advanced techniques and social engineering tailored specifically to mobile and macOS.

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We don’t just report on threats—we remove them

Cybersecurity risks should never spread beyond a headline. Keep threats off your devices by downloading Malwarebytes today.