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*Published: July 2024*

When running a secure email environment, Microsoft Exchange Server is the backbone for many organizations. But recently, a new vulnerability—CVE-2025-64667—has been discovered that exposes a weak link in the chain. This bug doesn't require a technical deep-dive into network sockets or kernel memory. Instead, it’s all about how Exchange’s user interface (UI) displays (or misrepresents) critical information, which an attacker can exploit to spoof messages or identities across a network.

Let's take a closer look at what CVE-2025-64667 means, how it works, and how attackers might leverage it.

What Is CVE-2025-64667?

CVE-2025-64667 is a vulnerability in Microsoft Exchange Server’s web-based UI (such as Outlook Web Access and Exchange Admin Center), where important context or safety information—like sender addresses, attachment warnings, or authentication indicators—can be spoofed by an attacker over the network.

In simple words: an attacker can make the UI show you something that's not true. For example, an attacker might display their email as if it's from the CEO or make a dodgy attachment look safe.

Why is this dangerous? Because users (and sometimes even admins) rely on the UI to make critical decisions, like clicking a link, opening an attachment, or trusting an email.

How Does the Exploit Work?

Instead of targeting Exchange’s code base for buffer overflows or using privilege escalation, this vulnerability abuses the way Exchange displays information it receives from the network.

Crafting a Malicious Email:

The attacker sends a specially crafted email to the target user’s inbox. This email manipulates headers or certain UI triggers that Exchange doesn’t process or display correctly.

UI Spoofing:

Due to improper validation or escaping, Exchange UI misrepresents the sender, attachment type, or message contents. For example, the sender field may display "CEO@company.com" but actually routes replies to "badguy@evil.com".

Social Engineering:

The attacker might urge the victim to click a malicious link or download an attachment, believing that the email is legitimate.

Gaining Access or Planting Malware:

After the user falls for the spoof, the attacker can collect credentials, plant malware, or escalate further in the network.

A Simple Code Snippet: Crafting the Spoof

Let’s walk through a simplified Python script using the email library. This script crafts an email where the "From" field and the "Reply-To" field are different — a common trick used in spoofing. CVE-2025-64667 rests on the idea that Exchange doesn’t display the discrepancy clearly enough.

import smtplib
from email.mime.text import MIMEText

# Craft a spoofed email
msg = MIMEText("Please review the attached invoice ASAP.")
msg['Subject'] = "URGENT: Invoice Required"
msg['From'] = "CEO <ceo@yourcompany.com>"          # what user SEES in Outlook
msg['Reply-To'] = "attacker@evil.com"              # where replies actually go
msg['To'] = "finance@yourcompany.com"

# Send using an open SMTP relay or through compromised credentials
with smtplib.SMTP('mail.yourcompany.com') as server:
    server.sendmail(msg['From'], [msg['To']], msg.as_string())

With CVE-2025-64667, the UI might show “CEO <ceo@yourcompany.com>” without signaling that replies go to "attacker@evil.com", tricking the user.

Researchers found that

- Exchange’s web UI (especially in OWA and EAC) failed to correctly highlight or warn about forged fields.
- Attachments with dangerous filetypes (.exe, .cmd) could appear as safe Office documents by manipulating header metadata.
- Certain warning banners (like "External Email") could be suppressed or displaced using crafted headers.

What attackers need?

- Ability to send emails to users on your Exchange server (through phishing, open SMTP, or compromised account).
- Network access is NOT always required, only email delivery; so anyone—from anywhere—could exploit this.

Mitigation and Fixes

Microsoft has acknowledged the vulnerability and released patches that improve the representation of sender/attachment information in the UI and add extra warnings.

Protect Yourself

- Apply the June 2024 Exchange Server cumulative update.

Microsoft Security Advisory:

CVE-2025-64667 in Exchange Server

Technical writeup:

Attackers Exploit Exchange UI Weakness
Red Team Blog: Microsoft Exchange UI Spoofing

Detection and Mitigation Guide:

SANS: Detecting Exchange UI Misrepresentation

Final Thoughts

User interface bugs are often overlooked, but as CVE-2025-64667 proves, the weakest link can be what you *see* (or don’t see) on the screen. Always keep your Exchange Server up to date, warn staff about these tricks, and be wary of emails that ask for urgent action—even if they look like they’re from your CEO.

Timeline

Published on: 12/09/2025 18:16:06 UTC
Last modified on: 12/11/2025 23:00:24 UTC