Subscribe to receive notifications of new posts:

SLP: a new DDoS amplification vector in the wild


2 min read

Earlier today, April 25, 2023, researchers Pedro Umbelino at Bitsight and Marco Lux at Curesec published their discovery of CVE-2023-29552, a new DDoS reflection/amplification attack vector leveraging the SLP protocol. If you are a Cloudflare customer, your services are already protected from this new attack vector.

Service Location Protocol (SLP) is a “service discovery” protocol invented by Sun Microsystems in 1997. Like other service discovery protocols, it was designed to allow devices in a local area network to interact without prior knowledge of each other. SLP is a relatively obsolete protocol and has mostly been supplanted by more modern alternatives like UPnP, mDNS/Zeroconf, and WS-Discovery. Nevertheless, many commercial products still offer support for SLP.

Since SLP has no method for authentication, it should never be exposed to the public Internet. However, Umbelino and Lux have discovered that upwards of 35,000 Internet endpoints have their devices’ SLP service exposed and accessible to anyone. Additionally, they have discovered that the UDP version of this protocol has an amplification factor of up to 2,200x, which is the third largest discovered to-date.

Cloudflare expects the prevalence of SLP-based DDoS attacks to rise significantly in the coming weeks as malicious actors learn how to exploit this newly discovered attack vector.

Cloudflare customers are protected

If you are a Cloudflare customer, our automated DDoS protection system already protects your services from these SLP amplification attacks.
To avoid being exploited to launch the attacks, if you are a network operator, you should ensure that you are not exposing the SLP protocol directly to the public Internet. You should consider blocking UDP port 427 via access control lists or other means. This port is rarely used on the public Internet, meaning it is relatively safe to block without impacting legitimate traffic. Cloudflare Magic Transit customers can use the Magic Firewall to craft and deploy such rules.

We protect entire corporate networks, help customers build Internet-scale applications efficiently, accelerate any website or Internet application, ward off DDoS attacks, keep hackers at bay, and can help you on your journey to Zero Trust.

Visit from any device to get started with our free app that makes your Internet faster and safer.

To learn more about our mission to help build a better Internet, start here. If you're looking for a new career direction, check out our open positions.

Follow on X

Alex Forster|@alex_forster
Omer Yoachimik|@OmerYoahimik

Related posts

May 30, 2024 1:00 PM

Disrupting FlyingYeti's campaign targeting Ukraine

In April and May 2024, Cloudforce One employed proactive defense measures to successfully prevent Russia-aligned threat actor FlyingYeti from launching their latest phishing campaign targeting Ukraine...