GoBGP accepts a zero-length AS_PATH attribute during BGP UPDATE decoding without marking it as malformed. Later, during validation for confederation eBGP peers, the code accesses the first element of the AS_PATH segments without checking if any segments exist, causing an index out of range panic. This vulnerability allows a remote unauthenticated confederation eBGP peer to send a malformed UPDATE that triggers a denial of service by crashing the receive goroutine or possibly the entire GoBGP process. The root cause is the lack of proper validation for empty AS_PATH attributes in the confederation eBGP validation path. A patch adds a check to reject empty AS_PATH attributes with a proper BGP message error.

A remote unauthenticated confederation eBGP peer can cause a denial of service by sending a single malformed BGP UPDATE message with a zero-length AS_PATH attribute. This leads to a runtime panic due to an unchecked index access, disrupting the BGP session and potentially terminating the GoBGP process. There is no impact on confidentiality, integrity, or authentication bypass, and no code execution or memory corruption is reported.

A patch is available that fixes the vulnerability by adding validation to reject zero-length AS_PATH attributes for confederation eBGP peers. Users should upgrade to GoBGP version 4.7.0 or later where this fix is applied. Until patched, operators should avoid accepting confederation eBGP peers that could send malformed AS_PATH attributes or implement network-level filtering to block malformed BGP UPDATE messages if feasible.