---
id: "CVE-2026-112112"
kind: "vulnerability"
aliases: ["CVE-2026-112112"]
title: "BIRD routing daemon: IPv6 FlowSpec check lets peers inject out-of-scope rules"
severity: "low"
cvss: 2.3
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["bgp", "bird", "flowspec", "ipv6", "network-operators", "runtime"]
not_affected_if: ["ipv4-only", "no-flow6-channel", "no-flowspec", "validation-disabled"]
published_at: "2026-10-18T23:16:56+00:00"
first_seen_at: "2026-10-23T21:57:17+00:00"
updated_at: "2026-10-25T04:49:54+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-112112", "first_seen_at": "2026-10-23T21:57:17+00:00"}]
---

# BIRD routing daemon: IPv6 FlowSpec check lets peers inject out-of-scope rules

BIRD, the CZ.NIC BGP routing daemon, fails to reject IPv6 FlowSpec destination prefixes with a nonzero offset when validation is enabled on a flow6 channel. An established BGP peer can get rules matching address space it is not authorized for, which may then propagate to downstream peers and filter or redirect traffic.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Run `birdc show protocols all` and check whether any BGP peer has a flow6 channel with FlowSpec import and validation enabled.
- Check the installed BIRD version with `bird --version` (or `birdc show status`) and compare it against the fixed release named in the NVD record.

## Fix

- Upgrade BIRD to the fixed release listed for CVE-2026-112112 (exact version unknown from the sources).
- Until patched, restrict which peers may send FlowSpec routes and tighten export policy for flow6 channels.

## Timeline

- 2026-10-23T21:57:17+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-112112

## From the sources

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.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_