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National Vulnerability Database

National Vulnerability Database

NVD

National Vulnerability Database
  1. Vulnerabilities

CVE-2026-40691 Detail

Description

In Unbound 1.9.0 up to and including 1.25.1, when a DNSCrypt query is received over TCP, the routine that encrypts the reply in place fails to bound the reply length against the destination buffer size. The size clamp that protects the UDP path is not applied on the TCP path, so a reply larger than 65504 bytes is shifted forward by 48 bytes inside a buffer of capacity equal to 'msg-buffer-size', writing past the end of the heap allocation. A single malicious encrypted query crashes the resolver and lead to denial of service. This vulnerability needs Unbound to be compiled with DNSCrypt support ('--enable-dnscrypt') and the 'dnscrypt:' clause to be configured and enabled for the listening interfaces.


Metrics

 
NVD enrichment efforts reference publicly available information to associate vector strings. CVSS information contributed by other sources is also displayed.
CVSS 4.0 Severity and Vector Strings:

NIST CVSS score
NIST: NVD
N/A
NVD assessment not yet provided.

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URL Source(s) Tag(s)
https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-40691.txt NLnet Labs

Weakness Enumeration

CWE-ID CWE Name Source
CWE-122 Heap-based Buffer Overflow NLnet Labs  
CWE-787 Out-of-bounds Write NLnet Labs  

Change History

2 change records found show changes

Quick Info

CVE Dictionary Entry:
CVE-2026-40691
NVD Published Date:
07/22/2026
NVD Last Modified:
07/22/2026
Source:
NLnet Labs