In early 2023, cybersecurity researchers uncovered a significant vulnerability in Microsoft SharePoint Server, cataloged as CVE-2023-23395. This "spoofing" vulnerability has the potential to expose organizations to phishing, data theft, and privilege escalation attacks if left unpatched. In this article, we’ll break down how the vulnerability works (with example code), assess the risk, show how attackers can exploit it, and guide you on how to stay protected. This article is written for everyone, and we’ll skip confusing jargon as much as possible.
What is CVE-2023-23395?
CVE-2023-23395 is a spoofing vulnerability in Microsoft SharePoint Server. Spoofing means an attacker tricks someone or something into thinking they are someone else. In this case, an attacker could cause SharePoint to send out emails that look like they come from a trusted internal system but are actually controlled by the attacker.
How Does the Vulnerability Work?
SharePoint is a collaboration tool, and it often sends notification emails—like when you share a document. These emails usually include links that are supposed to go back to your SharePoint server. But, due to poor validation, an attacker can craft a specially-crafted request so SharePoint’s emails include links to any site they want.
The Risk: If a user clicks a malicious link in what they believe is a genuine SharePoint email, the attacker can trick them into revealing credentials, downloading malware, or doing something else dangerous.
Technical Deep Dive
Let’s see an example of how this vulnerability is triggered. The root of the problem comes from SharePoint’s handling of a field called Source (or similar URLs) in user input. SharePoint fails to properly sanitize or validate the Source parameter embedded within notification emails.
SharePoint sends legitimate-looking notification email:
- The victim receives the email, which contains a link such as https://attacker.com/steal-info.
Example Manipulated URL
Suppose the attacker has access to your SharePoint server’s share dialog. They create a sharing link like this:
https://evil.com/fakepage" rel="nofollow">https://sharepoint.yourcompany.com/sites/team/_layouts/15/Doc.aspx?sourcedoc=abc&file=report.docx&action=default&Source=https://evil.com/fakepage
When SharePoint sends an email notification about this shared file, it includes the malicious Source URL. Clicking "Open" in the email takes the user directly to https://evil.com/fakepage.
Minimal PoC: How an attacker does it
Let's say the attacker uses PowerShell and SharePoint Management Shell to automate sending the bad share link:
# PowerShell snippet to share a doc with arbitrary Source
$siteUrl = "https://sharepoint.yourcompany.com/sites/team";
$docUrl = "/Shared%20Documents/Secret.docx"
$maliciousSource = "https://evil.com/phishing";
# Build the full Share URL
$shareUrl = "$siteUrl/_layouts/15/Doc.aspx?\
sourcedoc=$docUrl&file=Secret.docx&action=default&Source=$maliciousSource"
# Send the link via SharePoint's sharing feature
# (Details omitted for brevity; standard SharePoint sharing scripts/plugins)
It's that simple. No hacking into the server; just craft a special link and let SharePoint help deliver the trap.
SharePoint Server Subscription Edition (SPSE)
Cloud-hosted SharePoint Online was *not* impacted, according to Microsoft.
Microsoft’s Security Advisory (March 2023):
CVE-2023-23395 | Microsoft SharePoint Server Spoofing Vulnerability
Security Research Write-up from Akamai:
Critical SharePoint Authentication Bypass (CVE-2023-23395)
NIST National Vulnerability Database:
Real-World Impact: Why Does It Matter?
If your SharePoint Server is public-facing or used for company-wide communications, a spoofed email could lead to:
Privilege Escalation: Tricking admins into visiting crafted URLs.
Attackers may not need high-privilege access to exploit this; sometimes regular users can insert malicious Source parameters.
## How to Fix / Mitigate
Apply Microsoft’s patch immediately!
Check the official security update guide and install the latest SharePoint updates.
Conclusion
CVE-2023-23395 is dangerous because it turns SharePoint itself into a phishing tool. The best defense is keeping systems regularly patched and educating users not to trust all email links blindly. For technical admins, review audit logs and control who can generate outbound emails with custom parameters.
Stay secure, patch fast, and always be skeptical of odd-looking links—even if they appear to come from inside your organization!
*Written just for you, in clear language, by cyber professionals.*
Timeline
Published on: 03/14/2023 17:15:00 UTC
Last modified on: 03/20/2023 21:19:00 UTC