Preface: The core purpose of a BGP UPDATE is to tell another router some traffic it can (or can no longer) send to it. However, simply knowing directly what can be sent to another router is not very useful without context. Therefore, a BGP packet is divided into two parts: Network Layer Reachability Information (NLRI) data (also known as an IP address range) and attributes that help describe additional context about that reachability data.

Background:

One important flag is called the “transitive bit”:

If a BGP implementation does not understand an attribute and the transitive bit is set, it will copy it to another router. If the router does understand this attribute, it can apply its own policy. But in this way,  it allows possibly unknown information to propagate blindly through systems that do not understand the impact of what they are forwarding. 

Vulnerability details: The BGP daemon in Extreme Networks ExtremeXOS (aka EXOS) 30.7.1.1 allows an attacker (who is not on a directly connected network) to cause a denial of service (BGP session reset) because of BGP attribute error mishandling (for attribute 21 and 25). NOTE: the vendor disputes this because it is “evaluating support for RFC 7606 as a future feature” and believes that “customers that have chosen to not require or implement RFC 7606 have done so willingly and with knowledge of what is needed to defend against these types of attacks.”

Official announcement: Please refer to the official announcement for details – https://nvd.nist.gov/vuln/detail/CVE-2023-40457/change-record?changeRecordedOn=11/10/2024T19:15:13.817-0500