Improper Authorization in cobbler

Impact

If PAM is correctly configured and a user account is set to expired, the expired user-account is still able to successfully log into Cobbler in all places (Web UI, CLI & XMLRPC-API).

The same applies to user accounts with passwords set to be expired.

Patches

There is a patch for the latest Cobbler 3.3.2 available, however a backport will be done for 3.2.x.

Workarounds

• Delete expired accounts which are able to access Cobbler via PAM.
• Use chage -l <username> to lock the account. If the account has SSH-Keys attached then remove them completely.

References

• Originally discovered by @ysf at https://www.huntr.dev/bounties/c458b868-63df-414e-af10-47e3745caa1d/

How to test if my Cobbler instance is affected?

The following pytest test assumes that your PAM setup is correct. In case the added user is not able to login, this test does not make sense to be executed.

def test_pam_login_with_expired_user():
    # Arrange
    # create pam testuser
    test_username = "expired_user"
    test_password = "password"
    test_api = CobblerAPI()
    subprocess_1 = subprocess.run(
        ["perl", "-e", "'print crypt(\"%s\", \"%s\")'" % (test_username, test_password)],
        stdout=subprocess.PIPE
    )
    subprocess.run(["useradd", "-p", subprocess_1.stdout, test_username])
    # change user to be expired
    subprocess.run(["chage", "-E0", test_username])

    # Act
    result = pam.authenticate(test_api, test_username, test_password)

    # Assert - login should fail
    assert not result

For more information

If you have any questions or comments about this advisory:

• Open an issue in the Cobbler repository
• Ask in the Gitter/Matrix Chat
• Email us at [email protected]