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Vulnerability record · CVE-2026-81634 · published 16 September 2026

CVE-2026-81634: Nlnetlabs unbound heap-based buffer overflow vulnerability

Nlnetlabs · Unbound

In NLnet Labs Unbound up to and including 1.26.0, a 255 length query name with a large TCP response can lead to a heap buffer overflow during the RRSet canonicalisation routine. This is caused by missing to add the first owner name into the buffer length check. A malicious actor operating a malicious name server or tampering with an incoming response to Unbound (canonicalisation happens before DNSSEC validation), can trigger the vulnerability.

7.5 CVSS 3.1 High EPSS 0.48% · top 61.1% CWE-122 · Heap-based buffer overflow
7.5CVSS 3.1 base score
0.48%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
1References
23 Sep 2026Last modified by NVD

Description

In NLnet Labs Unbound up to and including 1.26.0, a 255 length query name with a large TCP response can lead to a heap buffer overflow during the RRSet canonicalisation routine. This is caused by missing to add the first owner name into the buffer length check. A malicious actor operating a malicious name server or tampering with an incoming response to Unbound (canonicalisation happens before DNSSEC validation), can trigger the vulnerability.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

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

References

LinkTags
https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-81634.txt PatchVendor Advisory

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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-2026-81634), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.