CVE-2026-49943

CZ.NIC BIRD Internet Routing Daemon through 2.19.0 contains a stack-based buffer overflow in the BGP ASPATH mask matching implementation in nest/a-path.c. The aspathmatch() function uses a fixed-size stack array of 2048 + 1 pmpos entries, while parsepath() expands ASPATH segments from a received BGP UPDATE without enforcing a corresponding capacity limit. When RFC 8654 BGP Extended Messages are enabled and a BIRD filter evaluates an AS path mask expression such as "bgppath ~ [= ... =]", an established BGP peer can send a long ASPATH containing more than 2048 expanded ASNs. This causes parsepath()/aspath_match() to write beyond the fixed stack buffer, resulting in a crash of the daemon. NOTE: reportedly, the Supplier's position is that a fix is not being prioritized because all network operators should already be rejecting routes with unusually long attributes.