NGINX project maintainers fix flaws in LDAP Reference Implementation

The maintainers of the NGINX web server project addressed a zero-day vulnerability in the Lightweight Directory Access Protocol (LDAP) Reference Implementation.

The maintainers of the NGINX web server project have released security updates to address a zero-day vulnerability that resides in its Lightweight Directory Access Protocol (LDAP) Reference Implementation.

The NGINX LDAP reference implementation uses LDAP to authenticate users of applications that are proxied by the NGINX web server.

NGINX Open Source and NGINX Plus are not affected, states the security advisory published by the company.

“Project maintainers addressed the security vulnerabilities in the NGINX LDAP reference implementation were publicly shared. We have determined that only the reference implementation is affected. NGINX Open Source and NGINX Plus are not themselves affected, and no corrective action is necessary if you do not use the reference implementation.” reads the advisory.

The advisory states that the LDAP reference implementation is impacted by the vulnerabilities when one of the following conditions apply:

  1. Command-line parameters are used to configure the Python daemon
  2. There are unused, optional configuration parameters
  3. LDAP authentication depends on specific group membership

An attacker could override the configuration parameters by sending specially crafted HTTP request headers and even bypass LDAP authentication.

“The Python daemon does not sanitize its inputs. Consequently, an attacker can use a specially crafted request header to bypass the group membership (memberOf) check and so force LDAP authentication to succeed even if the user being authenticated does not belong to the required groups. To mitigate against this, ensure that the backend daemon that presents the login form strips any special characters from the username field. In particular, it must remove the opening and closing parenthesis characters – ( ) – and the equal sign (=), which all have special meaning for LDAP servers.” continues the advisory. “The backend daemon in the LDAP reference implementation will be updated in this way in due course.”

NGINX project maintainers recommend users to strip special characters from the username field in the login form and update appropriate configuration parameters with an empty value (“”).

The advisory recommends removing the opening and closing parenthesis characters (“(” and “)”) and the equal sign (“=”), which all have special meaning for LDAP servers.

The flaws have been reported by Lucas Verney, valodzka and @_Blue_hornet.

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Pierluigi Paganini

(SecurityAffairs – hacking, LDAP)

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Pierluigi Paganini

Pierluigi Paganini is member of the ENISA (European Union Agency for Network and Information Security) Threat Landscape Stakeholder Group and Cyber G7 Group, he is also a Security Evangelist, Security Analyst and Freelance Writer. Editor-in-Chief at "Cyber Defense Magazine", Pierluigi is a cyber security expert with over 20 years experience in the field, he is Certified Ethical Hacker at EC Council in London. The passion for writing and a strong belief that security is founded on sharing and awareness led Pierluigi to find the security blog "Security Affairs" recently named a Top National Security Resource for US. Pierluigi is a member of the "The Hacker News" team and he is a writer for some major publications in the field such as Cyber War Zone, ICTTF, Infosec Island, Infosec Institute, The Hacker News Magazine and for many other Security magazines. Author of the Books "The Deep Dark Web" and “Digital Virtual Currency and Bitcoin”.

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