NLnet Labs Unbound up to 1.25.1 authentication replay

Summaryinfo

A vulnerability was found in NLnet Labs Unbound up to 1.25.1. It has been declared as critical. This affects an unknown part. Executing a manipulation can lead to authentication replay. This vulnerability appears as CVE-2026-46582. The attack may be performed from remote. There is no available exploit.

Detailsinfo

A vulnerability was found in NLnet Labs Unbound up to 1.25.1. It has been declared as critical. This vulnerability affects some unknown processing. The manipulation with an unknown input leads to a authentication replay vulnerability. The CWE definition for the vulnerability is CWE-294. A capture-replay flaw exists when the design of the product makes it possible for a malicious user to sniff network traffic and bypass authentication by replaying it to the server in question to the same effect as the original message (or with minor changes). As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

In NLnet Labs Unbound 1.6.0 up to and including 1.25.1, a replay of a wildcard rrset as another piece of data, could be briefly considered DNSSEC secure based only on the RRSIG validation and stored into cache, before later validation treats it as bogus based on NSEC validation. When the resolving thread puts secure on the rrset, and another thread that is on the serve expired path then picks up the updated rrset contents with the secure status for a reply, it can be used to change a specific record, next to a wildcard that could be covered by the wildcard, into the wildcard. A malicious actor can exploit the possible poisonous effect by having any DNSSEC-singed domain (irrelevant to the victim domain) and a CNAME wrapper record that points to a record next to a wildcard (that could be covered by the wildcard). Then quering Unbound for the wildcard sibling record would seed the secure message. A later (after expiry) query for the CNAME wrapper would need to resolve the target sibling record. If the wildcard replay is injected into the response, the wildcard rrset will update the expired sibling record with a secure status before completing proper wildcard validation with NSEC records and eventually treating the CNAME wrapper answer as bogus. The updated poisoned rrset is now secure and points to the wildcard. This vulnerability is explicit for the serve expired path and needs injection of the signed wildcard rrset without the NSEC accompanying rrset.

The advisory is available at nlnetlabs.nl. This vulnerability was named CVE-2026-46582 since 06/22/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. The technical details are unknown and an exploit is not available. This vulnerability is assigned to T1040 by the MITRE ATT&CK project.

Upgrading to version 1.25.2 eliminates this vulnerability.

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Productinfo

Vendor

• NLnet Labs

Name

• Unbound

Version

• 1.25.0
• 1.25.1

CPE 2.3info

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CPE 2.2info

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