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CVE-2026-81634

Possible heap buffer overflow during DNSSEC canonicalization

CVSS 3.1 7.5 HIGHCheck source for fixed versionsKEV status unknown

Original advisory

Historical advisory recorded 23 Oct 2026 15:48:27 UTC. Read the latest advisory.

cve-program · CVE-2026-81634

Published

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.

Read the publisher's advisory

Affected versions, risk and source history

cve-program · CVE-2026-81634

Published

Unbound

Vendor product

Publisher's version information

Shown as published. These rules are not interpreted as NuGet package version ranges.

{
                    "vendor": "NLnet Labs",
                    "product": "Unbound",
                    "versions": [
                        {
                            "version": "0",
                            "status": "affected",
                            "lessThan": "1.26.1",
                            "versionType": "semver"
                        }
                    ],
                    "defaultStatus": "unaffected"
                }

Original source record · Cite this exact observation · Complete original publisher JSON