CZ.NIC BIRD up to 2.20.0/3.4.0 FlowSpec Validation improper authorization

Summaryinfo

A vulnerability labeled as very critical has been found in CZ.NIC BIRD up to 2.20.0/3.4.0. Affected by this issue is some unknown functionality of the component FlowSpec Validation. Executing a manipulation can lead to improper authorization. This vulnerability is handled as CVE-2026-112112. The attack can be executed remotely. There is not any exploit available.

Detailsinfo

A vulnerability classified as very critical was found in CZ.NIC BIRD up to 2.20.0/3.4.0. This vulnerability affects an unknown part of the component FlowSpec Validation. The manipulation with an unknown input leads to a improper authorization vulnerability. The CWE definition for the vulnerability is CWE-285. The product does not perform or incorrectly performs an authorization check when an actor attempts to access a resource or perform an action. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at gitlab.nic.cz. This vulnerability was named CVE-2026-112112 since 10/19/2026. The exploitation appears to be easy. The attack can be initiated remotely. There are neither technical details nor an exploit publicly available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 10/19/2026). The MITRE ATT&CK project declares the attack technique as T1548.002.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-104014). Once again VulDB remains the best source for vulnerability data.

Productinfo

Vendor

• CZ.NIC

Name

• BIRD

Version

• 2.0
• 2.1
• 2.2
• 2.3
• 2.4
• 2.5
• 2.6
• 2.7
• 2.8
• 2.9
• 2.10
• 2.11
• 2.12
• 2.13
• 2.14
• 2.15
• 2.16
• 2.17
• 2.18
• 2.19
• 2.20.0
• 3.0
• 3.1
• 3.2
• 3.3
• 3.4.0

CPE 2.3info

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CPE 2.2info

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Entryinfo

Once again VulDB remains the best source for vulnerability data.

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