CVE-2026-40691
HIGH
7,5
Source: [email protected]
Attack Vector: network
Attack Complexity: low
Privileges Required: none
User Interaction: none
Scope: unchanged
Confidentiality: none
Integrity: none
Availability: high
Description
AI Translation Available
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.
122
Heap-based Buffer Overflow
DraftCommon Consequences
Security Scopes Affected:
Availability
Integrity
Confidentiality
Access Control
Other
Potential Impacts:
Dos: Crash, Exit, Or Restart
Dos: Resource Consumption (Cpu)
Dos: Resource Consumption (Memory)
Execute Unauthorized Code Or Commands
Bypass Protection Mechanism
Modify Memory
Other
Applicable Platforms
Languages:
Memory-Unsafe, C, C++
787
Out-of-bounds Write
DraftCommon Consequences
Security Scopes Affected:
Integrity
Availability
Other
Potential Impacts:
Modify Memory
Execute Unauthorized Code Or Commands
Dos: Crash, Exit, Or Restart
Unexpected State
Applicable Platforms
Languages:
Memory-Unsafe, C, C++, Assembly
Technologies:
ICS/OT
Application
Unbound by Nlnetlabs
Version Range Affected
From
1.9.0
(inclusive)
To
1.25.2
(exclusive)
CPE Identifier
View Detailed Analysis
cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*
Common Platform Enumeration - Standardized vulnerability identification
https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-40691.txt