Adobe patched CVE-2026-48294, a flaw in Adobe Acrobat Chrome extension that could let attackers steal WhatsApp Web chats by luring users to a webpage.

Guardio Labs researcher Shaked Biner disclosed HermeticReader, a vulnerability chain in the Adobe Acrobat Chrome extension that allowed any attacker-controlled webpage to silently steal a visitor’s WhatsApp chats, contacts, profile name, and message previews in plain text. The extension sits on roughly 329 million browsers. No malware, no phished password, no compromised session cookie — just visiting the wrong page was enough.

“Read the prerequisites list of this exploit chain and the discomfort sets in: no malware is installed, no password is phished, no session cookie is touched. There is no zero-day in WhatsApp.” reads the report published by Guardio Labs. “The attacker needs no Adobe account and no foothold on the machine. Only for the victim to visit a simple attacker-controlled static page.”

The attack chains three separate flaws in the extension’s internal messaging system. None of them are dramatic on their own. Together they hand an attacker full DOM control over an open WhatsApp Web tab.

The first flaw is that the extension’s web-accessible resource pages, frame.html, searchWidget.html, and others, can be embedded as hidden iframes by any website. Those pages parse a JSON blob directly from their URL query string and relay it to the extension’s service worker as a message.

“Because that script runs inside chrome-extension://efaidn…/, the service worker sees its message as coming from a trusted internal source. The extension’s own identity becomes the attacker’s mask. The page can set any fields on the message , type, key, value, anything else.” continues the report. “Two fields are not free: panel_op has to be set to "load-frictionless" so that frame.js takes the relay code path at all, and main_op is overwritten to "relay_to_content" on the way out.”

The service worker’s message listener never checks the sender. Its storage writer has no allowlist on what can be written. Any page can write any key into the extension’s local storage in zero clicks.

That storage write matters because of the third flaw: Adobe’s Hermes engine, the component that handles WhatsApp Web integration, activates based on a feature flag read from local storage. Write the right key – floodgate-add = "dc-cv-hermes" – and Hermes arms immediately. With Hermes running, the attacker controls a command dispatcher inside WhatsApp’s tab that can inject HTML, invoke methods on any DOM node, submit forms, and relay messages back to the service worker. One of those commands, APPEND_HTML_TO_TARGET, can replace WhatsApp’s login QR code with an attacker-controlled one, meaning anyone who scans it to link a new device pairs the attacker’s session instead.

The data exfiltration technique is what makes the research genuinely clever.

“We never asked the extension to read anything. We asked WhatsApp to submit itself to us – and it did.” states the report.

The attack injects a POST form into WhatsApp’s DOM, then uses the ELEMENT_OPERATION command to physically move WhatsApp’s entire body node into the form’s option element. Because an option element with no value attribute submits its text content, and because WhatsApp’s content security policy contains no form-action directive, submitting the form sends the entire rendered page, chat list, contact names, message text, to the attacker’s server. WhatsApp does the exfiltration itself.

Guardio found this within hours of Adobe shipping version 26.5.2.1 on June 3, using a custom agentic AI system that unpacked and analyzed the extension’s 344 obfuscated JavaScript files, mapped code diffs against previously analyzed flows, and worked through a 138-case service-worker message dispatcher.

“The Agentic AI Research harness is not only a clever and innovative way to research – it already became mandatory! From a new version release trigger, the work is shared: The agent unpacks the bundle, beautifies 344 obfuscated JavaScript files, finds the code diffs and maps them against already mapped and analyzed flows, continues to map a 138-case service-worker message dispatcher, and so much more.” states Guardio Labs. “At this time, we’ve steered the analysis toward what is actually reachable and worth proving, cleared dead ends, and presented plausible ideas and attack vectors to pursue. That combination is what collapsed the time line into hours instead of days, weeks or even months.”

Adobe’s response matched the speed: acknowledged, patched, and shipped within the same weekend the report arrived. CVE-2026-48294 was issued days later.

The structural lesson here isn’t about any single clever trick. Twelve individually unremarkable shortcuts in message passing, storage handling, feature flags, and host matching composed into a chain that reached 329 million browsers. The era in which a high-install extension could rely on nobody looking at the plumbing closely is ending, for defenders and attackers alike.

Follow me on Twitter: @securityaffairs and Facebook and Mastodon

Pierluigi Paganini

(SecurityAffairs – hacking, Adobe Acrobat)

An email attachment leads to the installation of a malicious Chrome extension. Researchers say it is part of a Windows backdoor delivered via a phishing email. The malware abuses Chrome Native Messaging to move control from the browser into the host system. Its most notable trick isn’t the phishing lure itself, but the way it uses legitimate browser and Windows features to run PowerShell and collect data while staying inside expected workflows.

The attack starts with an email attachment disguised as a PDF. The file uses the misleading extension .pfd.js to look like a PDF document, but it’s actually an obfuscated JavaScript file that drops additional files into the temporary folder and starts the rest of the infection chain.

As part of that chain, a PowerShell script prepares a Chrome extension and changes Chrome policy settings so that the extension can be installed. The malware makes the installation appear to be an administrator-controlled deployment rather than a normal extension installation.

Once active, the extension and its native companion collect browser cookies, open tabs, URLs, language settings, and fingerprinting data. The operators also use the setup as a remote command channel, sending instructions that can launch PowerShell and enumerate the contents of the C: drive.

With the stolen authenticated session cookies, the attackers can hijack active browser sessions rather than just stealing passwords, which is more useful to them as it lets them access accounts already logged in on the victim’s browser, bypassing multi-factor authentication (MFA).

The most interesting aspect of the attack is its abuse of Chrome Native Messaging as a bridge between the browser sandbox and the operating system. Chrome allows extensions to communicate with a registered native host, and the attackers weaponized that legitimate feature to make the extension a controller for local code execution. The extension doesn’t launch PowerShell directly. Instead, it sends messages to the native host, which then launches or interacts with PowerShell on the host system.

How to stay safe

The first line of defense against attacks of this kind is to avoid opening email attachments unless you can verify the sender. In addition:

• Always check the real file extension instead of relying on the displayed filename.
• Use an up-to-date, real-time anti-malware solution to detect and block malicious activity.
• Check the installed Chrome extensions on your device and remove any you don’t recognize or no longer use.
• To be extra cautious, sign out of important accounts when you’re finished. That invalidates your session, so even if someone has stolen your session cookie, they won’t be able to use it to access your account.
• Regularly check the login history for important accounts. Many online services let you see which devices have signed in, when, and from where.

IOCs

Attachment:

Fattura-2819889242.pfd.js (displayed as Fattura-26189991026.pdf)

Malicious files:

client_124578.exe
d3d11.dll

Chrome extension:

Name: Cloud vn105rkj64
ID: gghagmhimhgfeajfdmjkgmmehbokmglg

Domain:

ext2[.]info

This is blocked by Malwarebytes Browser Guard, our free browser extension that blocks ads, trackers, malware, and more.

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