NLnet Labs Unbound 1.6.2 up to and including version 1.25.0 has a denial of service vulnerability when compiled with DNSCrypt support ('--enable-dnscrypt'). A bad DNSCrypt query could underflow Unbound's DNSCrypt packet reading procedure that may lead to heap overflow. A malicious actor can exploit the vulnerability with a single bad DNSCrypt query that its decrypted plaintext consists entirely of '0x00' bytes and does not contain the expected '0x80' marker. Unbound would then start reading more bytes than necessary until it finds a non-'0x00' byte. Based on the underlying memory allocator and the memory layout, it could lead to heap overflow while reading followed by a crash. Likelihood of a crash is low, since it relies heavily on the underlying memory allocator and the memory layout. If the heap overflow does not happen, Unbound's later packet checks will deny the packet. Unbound 1.25.1 contains a patch with a fix to bound reading in the given buffer space.

Project Subscriptions

No data.

Advisories

No advisories yet.

Fixes

Solution

This issue is fixed starting with version 1.25.1


Workaround

No workaround given by the vendor.

History

Wed, 20 May 2026 10:00:00 +0000

Type Values Removed Values Added
Description NLnet Labs Unbound 1.6.2 up to and including version 1.25.0 has a denial of service vulnerability when compiled with DNSCrypt support ('--enable-dnscrypt'). A bad DNSCrypt query could underflow Unbound's DNSCrypt packet reading procedure that may lead to heap overflow. A malicious actor can exploit the vulnerability with a single bad DNSCrypt query that its decrypted plaintext consists entirely of '0x00' bytes and does not contain the expected '0x80' marker. Unbound would then start reading more bytes than necessary until it finds a non-'0x00' byte. Based on the underlying memory allocator and the memory layout, it could lead to heap overflow while reading followed by a crash. Likelihood of a crash is low, since it relies heavily on the underlying memory allocator and the memory layout. If the heap overflow does not happen, Unbound's later packet checks will deny the packet. Unbound 1.25.1 contains a patch with a fix to bound reading in the given buffer space.
Title Packet of death with DNSCrypt
Weaknesses CWE-125
CWE-166
References
Metrics cvssV4_0

{'score': 4.6, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Green'}


Projects

Sign in to view the affected projects.

cve-icon MITRE

Status: PUBLISHED

Assigner: NLnet Labs

Published:

Updated: 2026-05-20T09:17:47.920Z

Reserved: 2026-05-07T10:07:51.839Z

Link: CVE-2026-32792

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-05-20T10:16:26.277

Modified: 2026-05-20T10:16:26.277

Link: CVE-2026-32792

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

No data.

Weaknesses