NLnet Labs Unbound up to 1.6.2/1.25.1 Respip redirect

Summaryinfo

A vulnerability, which was classified as problematic, has been found in NLnet Labs Unbound up to 1.6.2/1.25.1. Affected by this vulnerability is an unknown functionality of the component Respip. This manipulation causes redirect. This vulnerability is tracked as CVE-2026-50243. The attack is possible to be carried out remotely. No exploit exists.

Detailsinfo

A vulnerability was found in NLnet Labs Unbound up to 1.6.2/1.25.1. It has been declared as problematic. Affected by this vulnerability is an unknown functionality of the component Respip. The manipulation with an unknown input leads to a redirect vulnerability. The CWE definition for the vulnerability is CWE-601. A web application accepts a user-controlled input that specifies a link to an external site, and uses that link in a Redirect. This simplifies phishing attacks. As an impact it is known to affect integrity. The summary by CVE is:

In NLnet Labs Unbound 1.6.2 up to and including 1.25.1, when Unbound is configured with the 'respip' module in front of the validator together with a 'response-ip' redirect rule or an RPZ file with an RPZ-IP trigger, the rewriting handler does not check the security status of the upstream answer and can instead rewrite a BOGUS A/AAAA answer to point to an operator's configured IP. If the validator finds an expired or otherwise invalid RRSIG on an answer whose A record falls within a 'response-ip'/RPZ configuration, the answer is still rewritten and given a hard coded security level of INSECURE. This results in the client receiving an INSECURE NOERROR reply rewritten by the operator's configured IP. A malicious actor can exploit the possible poisonous effect by spoofing a BOGUS A/AAAA answer that falls inside the operator's configured subnet rewrites. Such DNSSEC protected answers are then insecurely redirected to the operator's configured target.

It is possible to read the advisory at nlnetlabs.nl. This vulnerability is known as CVE-2026-50243 since 06/22/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. It demands that the victim is doing some kind of user interaction. The technical details are unknown and an exploit is not publicly available. The attack technique deployed by this issue is T1204.001 according to MITRE ATT&CK.

Upgrading to version 1.25.2 eliminates this vulnerability.

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Productinfo

Vendor

• NLnet Labs

Name

• Unbound

Version

• 1.6.0
• 1.6.1
• 1.6.2
• 1.25.0
• 1.25.1

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CPE 2.2info

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