← Vulnerability feed

Vulnerability record · CVE-2026-42944 · published 20 May 2026

CVE-2026-42944: Nlnetlabs unbound out-of-bounds write vulnerability

Nlnetlabs · Unbound

NLnet Labs Unbound 1.14.0 up to and including version 1.25.0 has a vulnerability that results in heap overflow when encoding multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options in the reply packet. The relevant options ('nsid', 'answer-cookie', 'pad-responses' (default)) need to be enabled for the vulnerability to be exploited. An adversary who can query Unbound can exploit the vulnerability by attaching multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options to the query. A flaw in the size calculation of the EDNS field truncates the correct value which allows the encoder to overflow the available space when writing. Those two combined lead to a heap overflow write of Unbound controlled data and eventually a crash. Unbound 1.25.1 contains a patch with a fix to de-duplicate the EDNS options and a fix to prevent truncation of the EDNS field size calculation.

8.7 CVSS 4.0 High EPSS 0.78% · top 46.0% CWE-197 · CWE-197CWE-787 · Out-of-bounds write
8.7CVSS 4.0 base score
0.78%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
8References
26 Aug 2026Last modified by NVD

Description

NLnet Labs Unbound 1.14.0 up to and including version 1.25.0 has a vulnerability that results in heap overflow when encoding multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options in the reply packet. The relevant options ('nsid', 'answer-cookie', 'pad-responses' (default)) need to be enabled for the vulnerability to be exploited. An adversary who can query Unbound can exploit the vulnerability by attaching multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options to the query. A flaw in the size calculation of the EDNS field truncates the correct value which allows the encoder to overflow the available space when writing. Those two combined lead to a heap overflow write of Unbound controlled data and eventually a crash. Unbound 1.25.1 contains a patch with a fix to de-duplicate the EDNS options and a fix to prevent truncation of the EDNS field size calculation.

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-42944.txt MitigationVendor Advisory
https://access.redhat.com/errata/RHSA-2026:19752
https://access.redhat.com/errata/RHSA-2026:23231
https://access.redhat.com/errata/RHSA-2026:24365
https://access.redhat.com/errata/RHSA-2026:24369
https://access.redhat.com/security/cve/CVE-2026-42944
https://bugzilla.redhat.com/show_bug.cgi?id=2479774
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-42944.json

Track CVE-2026-42944 inside VULONE

Watch it alongside the ransomware crews, C2 infrastructure and forum chatter that reference it, query it through the API and pull it into your SIEM over TAXII.

Start free Open in platform

Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.8CVE-2019-25032Nlnetlabs unbound integer overflow vulnerabilityUnbound before 1.9.5 allows an integer overflow in the regional allocator via regional_alloc. NOTE: The vendor disputes that this is a vulnerability.…EPSS 2.2%9.8CVE-2019-25033Nlnetlabs unbound integer overflow vulnerabilityUnbound before 1.9.5 allows an integer overflow in the regional allocator via the ALIGN_UP macro. NOTE: The vendor disputes that this is a vulnerabil…EPSS 1.8%9.8CVE-2019-25034Nlnetlabs unbound integer overflow vulnerabilityUnbound before 1.9.5 allows an integer overflow in sldns_str2wire_dname_buf_origin, leading to an out-of-bounds write. NOTE: The vendor disputes that…EPSS 2.0%9.8CVE-2019-25035Nlnetlabs unbound out-of-bounds write vulnerabilityUnbound before 1.9.5 allows an out-of-bounds write in sldns_bget_token_par. NOTE: The vendor disputes that this is a vulnerability. Although the code…EPSS 2.0%9.8CVE-2019-25038Nlnetlabs unbound integer overflow vulnerabilityUnbound before 1.9.5 allows an integer overflow in a size calculation in dnscrypt/dnscrypt.c. NOTE: The vendor disputes that this is a vulnerability.…EPSS 2.0%9.8CVE-2019-25039Nlnetlabs unbound integer overflow vulnerabilityUnbound before 1.9.5 allows an integer overflow in a size calculation in respip/respip.c. NOTE: The vendor disputes that this is a vulnerability. Alt…EPSS 2.0%9.8CVE-2019-25042Nlnetlabs unbound out-of-bounds write vulnerabilityUnbound before 1.9.5 allows an out-of-bounds write via a compressed name in rdata_copy. NOTE: The vendor disputes that this is a vulnerability. Altho…EPSS 2.0%9.1CVE-2026-81642Nlnetlabs unbound heap-based buffer overflow vulnerabilityIn NLnet Labs Unbound up to and including 1.26.0, a vulnerability was found in the DNSSEC validator that enables denial of service and possible remot…EPSS 0.96%

Source: NIST National Vulnerability Database (record CVE-2026-42944), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.