CVE-2026-49943 Memory corruption in BIRD
A remote BGP peer can crash the BIRD daemon via a stack buffer overflow in AS_PATH matching when Extended Messages are enabled.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-49943?
CVE-2026-49943 is a medium-severity memory corruption vulnerability in NIC BIRD, published on 2 Jun 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
CZ.NIC BIRD Internet Routing Daemon through 2.19.0 contains a stack-based buffer overflow in the BGP AS_PATH mask matching implementation in nest/a-path.c. The as_path_match() function uses a fixed-size stack array of 2048 + 1 pm_pos entries, while parse_path() expands AS_PATH 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 "bgp_path ~ [= ... =]", an established BGP peer can send a long AS_PATH containing more than 2048 expanded ASNs. This causes parse_path()/as_path_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.
Weakness: CWE-121
Which versions are affected by CVE-2026-49943?
How do I fix CVE-2026-49943?
No fix has been published for CVE-2026-49943 yet. Limit exposure of the affected software until one is available.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-49943 being exploited?
There is no known exploitation of CVE-2026-49943 in the wild and no public exploit code.
Public exploit code: 1 proofs of concept on GitHub.
Sources
Also known as DEBIAN-CVE-2026-49943, GHSA-64c8-8qx9-25r7, UBUNTU-CVE-2026-49943.