CVE-2026-120033: frr: bgpd Send Hold Timer expiry bypasses the FSM, leaving a phantom Established session or crashing bgpd with Graceful Restart
In FRRouting 10.1 and later, bgpd does not correctly close a BGP session when the Send Hold Timer (RFC 9687) expires, i.e. when a neighbor has stopped accepting data from the router for twice the hold time. The connection is closed, but bgpd still considers the session to be up.
A BGP neighbor that keeps sending KEEPALIVEs but stops reading from its connection, at a time when the router has a large amount of data to send to it (for example while sending it a full routing table), can cause one of the following:
If the neighbor announced Graceful Restart support: bgpd crashes shortly after the session is closed (after the neighbor's announced restart time plus one keepalive interval), taking down all BGP sessions on the router. The neighbor can repeat this each time bgpd restarts. Otherwise: the session stays stuck in the Established state. The neighbor's routes stay installed and keep being advertised to other peers, and the neighbor cannot reconnect until an operator runs "clear bgp <neighbor>".
The neighbor does not need to be malicious; an overloaded or stuck peer can trigger the same behavior.
Required configuration: no special configuration is needed. Any BGP neighbor with an established session can trigger the issue under default settings, for example:
router bgp 65001 neighbor 192.0.2.2 remote-as 65002
Graceful Restart helper mode, which leads to the crash, is enabled by default. With default timers (keepalive 60s, hold time 180s), the session is closed about 6 minutes after the neighbor stops reading.
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Operational
Run "clear bgp <neighbor>" to clear the phantom Established session and allow the neighbor to reconnect.
Event History
Frequently Asked Questions
Which deployments are affected?
FRRouting 10.1 and later are affected. No special configuration is required; the issue can be triggered by a BGP neighbor that continues sending KEEPALIVEs while no longer accepting data from the router.
What conditions are needed to trigger the issue?
The peer must stop reading from its BGP connection long enough for the Send Hold Timer to expire, while bgpd has a large amount of data to send, such as during full routing-table advertisement. The peer does not need to be malicious; an overloaded or stuck peer can produce the same condition.
How does Graceful Restart support change the impact?
If the neighbor announced Graceful Restart support, bgpd can crash shortly after the connection closes, taking down all BGP sessions on the router. The peer can repeat the condition after bgpd restarts.
What happens when the affected neighbor does not support Graceful Restart?
The session can remain stuck in the Established state even though the connection has closed. Its routes remain installed and advertised to other peers, and the neighbor cannot reconnect until an operator runs "clear bgp <neighbor>".