March 23, 2023
Number of CLDAP reflectors increased by 60% in 2022, amplifying DDoS risks |

Number of CLDAP reflectors increased by 60% in 2022, amplifying DDoS risks |

Recent findings indicate that reflection attacks, in which vulnerable Microsoft servers are exploited to overwhelm websites with network traffic resulting in a Distributed Denial of Service (DDoS) attack, are on the rise. According to Lumen’s Black Lotus Labs, thousands of misconfigured CLDAP (Connectionless Lightweight Directory Access Protocol) instances enable these attacks.

Lumen Technologies’ threat intelligence arm, Black Lotus Labs, discovered nearly 12,000 misconfigured servers with CLDAP (Microsoft’s LDAP iteration), up 60% from 2021. Hackers are exploiting these servers Vulnerable CLDAPs that act as reflectors to conduct DDoS attacks.

A reflector is a vulnerable third-party server that hackers can trick into bombarding a target website with heavy traffic, resulting in a DDoS attack. Meanwhile, CLDAP is a protocol used to access, retrieve, and maintain user and system data (such as usernames, passwords, email addresses, etc.) to and from Microsoft Active Directory.

The main difference between CLDAP and LDAP is that the former uses User Datagram Protocol (UDP), which is likely to be used for reflection if connected through the open internet. UDP is safe when not connected to the Internet.

“Despite the industry’s strong understanding of the mechanics of UDP reflection, as well as the fact that most of these reflection-vulnerable UDP services are accidental setups, we continue to find many vulnerable services ready and waiting to generate a voluminous stream of unwanted traffic directed to a DDoS target of choice,” Lumen noted.

CLDAP reflectors in October 2022 (Source: Black Lotus Labs)

As the chart shows, nearly 85% of 12,142 reflectors emerged in the last 12 months after a period of decline between 2017 and 2020. “After their discovery, the total number of open CLDAP reflectors dropped, likely due to the awareness brought by media attention. However, the spike in DDoS that occurred at the start of the pandemic in 2020 led to a return of CLDAP thinking,” Lumen explained.

Learn more: GitHub High-Severity Vulnerability Exposed 10,000 Packages to Repojacking

Some of the most prominent CLDAP reflectors discovered by Lumen belonged to an anonymous religious organization, a retail company based in North America, and a telecommunications provider in the same region. To understand the intensity, reflectors belonging only to religious organizations generated a DDoS incident of up to 17 Gbps.

A 17 Gbps DDoS attack might not be quite so scary, although it is “perhaps powerful enough to DoS some less well-provisioned servers on its own.” In theory, a hundred of them, working in unison, could generate a terabit per second of attack traffic,” Lumen explained.

A simple workaround to thwart DDoS attacks based on CLDAP reflectors is to take them offline from the open Internet and leave them online only if absolutely necessary. For CLDAP instances that need to stay online, Lumen recommended the following:

  • Disable UDP: On versions of MS Server that support LDAP ping over LDAP TCP service, disable UDP service and access LDAP ping via TCP.
  • Apply flow restrictors: If the version of Microsoft Server does not support LDAP ping over TCP, limit the traffic generated by the 389/UDP service to prevent its use in DDoS.
  • firewall: If the Microsoft Server version does not support LDAP ping over TCP, a firewall accesses the port so that only your legitimate clients can access the service.

Lumen also suggested implementing network defenders, such as Reverse Path Forwarding (RPF), to prevent IP traffic spoofing.

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