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CVE-2025-2256: Unauthorized SAML Response Exploit in GitLab

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Overview

The vulnerability identified as CVE-2025-2256 is a serious security flaw found in various versions of GitLab CE/EE. The issue lies in the handling of Security Assertion Markup Language (SAML) responses. An attacker, without necessary authorization, could potentially send multiple concurrent large SAML responses, rendering the GitLab instance unresponsive to legitimate users. This vulnerability matters as it can lead to a potential system compromise or data leakage.

Vulnerability Summary

CVE ID: CVE-2025-2256
Severity: High (7.5 CVSS score)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: System compromise or data leakage

Affected Products

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Product | Affected Versions

GitLab CE/EE | All versions from 7.12 before 18.1.6, 18.2 before 18.2.6, and 18.3 before 18.3.2

How the Exploit Works

The exploit operates by sending numerous concurrent large SAML responses to the GitLab server. The system lacks the capability to manage such a large volume of SAML responses concurrently. This leads to an exhaustion of system resources, rendering the GitLab instance unresponsive to legitimate user requests.

Conceptual Example Code

This is a conceptual example of how the vulnerability might be exploited. The attacker sends numerous unauthorized SAML responses to the GitLab server:

POST /saml/consume HTTP/1.1
Host: gitlab.example.com
Content-Type: application/xml
<samlp:Response ...>
<saml:Assertion ...>
<saml:Subject ...>
<!-- Insert large payload here -->
</saml:Subject>
</saml:Assertion>
</samlp:Response>

This conceptual example could be repeated multiple times concurrently to overload the system.

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Disclaimer:

The information and code presented in this article are provided for educational and defensive cybersecurity purposes only. Any conceptual or pseudocode examples are simplified representations intended to raise awareness and promote secure development and system configuration practices.

Do not use this information to attempt unauthorized access or exploit vulnerabilities on systems that you do not own or have explicit permission to test.

Ameeba and its authors do not endorse or condone malicious behavior and are not responsible for misuse of the content. Always follow ethical hacking guidelines, responsible disclosure practices, and local laws.

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