CVE-2026-55717

Published: Lug 22, 2026 Last Modified: Lug 24, 2026
ExploitDB:
Other exploit source:
Google Dorks:
MEDIUM 5,9
Source: [email protected]
Attack Vector: network
Attack Complexity: high
Privileges Required: none
User Interaction: none
Scope: unchanged
Confidentiality: none
Integrity: none
Availability: high

Description

AI Translation Available

In NLnet Labs Unbound 1.10.0 up to and including 1.25.1, when 'serve-expired: yes' is set together with a 'response-ip: <net> redirect' /'response-ip-data: <net> CNAME <target>' rule (or the RPZ 'rpz-cname-override' equivalent), a remote client who controls any delegated domain can crash the daemon. The serve-expired-client-timeout callback runs a two-pass loop to chase the respip-generated CNAME alias; on the second pass it resets 'alias_rrset' but not 'partial_rep'. Later, this inconsistency leads to a NULL pointer dereference and an eventual crash. A malicious actor can exploit the vulnerability by controlling any zone that replies with an A/AAAA record that falls inside the configured response-ip/rpz subnet. By delaying the answer when the previous record has expired, the vulnerable path of 'serve-expired-client-timeout' is taken leading to denial of service via the server crash.

476

NULL Pointer Dereference

Stable
Abstraction: Base Structure: Simple
Common Consequences
Security Scopes Affected:
Availability Integrity Confidentiality
Potential Impacts:
Dos: Crash, Exit, Or Restart Execute Unauthorized Code Or Commands Read Memory Modify Memory
Applicable Platforms
Languages: C, C++, Java, C#, Go
Likelihood of Exploit: Medium
View CWE Details
Application

Unbound by Nlnetlabs

Product Information
Vendor Nlnetlabs
Product Unbound
Version Range Affected
From 1.10.0 (inclusive)
To 1.25.2 (exclusive)
cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*
Common Platform Enumeration - Standardized vulnerability identification
https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-55717.t…
https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-55717.txt