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NVD description
An IPv6 FlowSpec validation bypass in the CZ.NIC BIRD Internet Routing Daemon allows an established BGP peer to inject FlowSpec rules matching destinations outside the address space authorized by the unicast-route validation procedure. With validation enabled on the receiving flow6 channel, BIRD fails to reject a destination prefix component with a nonzero offset, contrary to RFC 8956 section 5. It validates a reconstructed prefix with zero-filled skipped bits, although the original FlowSpec component can match a broader set of IPv6 addresses. Given a suitable unicast route from the peer, the rule can pass validation and, where export policy permits, be propagated to downstream peers. Downstream enforcement may cause unauthorized traffic filtering or redirection.
Priority
LOW
Exploitation
NONE
PoC
NONE
Patch
NONE
Momentum
NONE
A BIRD FlowSpec bypass lets a BGP peer filter IPv6 space it never announced. Scored 2.3 low, every downstream-impact metric set to none. No fixed release — the newest BIRD is the affected one. No exploitation reported. https://severitydaily.com/bird-cve-2026-112112-ipv6-flowspec-nonzero-offset-validation-bypass-2-3-low-no-fixed-release/