{"id":"CVE-2026-81634","title":"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","summary":"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 …","severity":"high","cvss":7.5,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","cwe":["CWE-122","CWE-120"],"vendor":"nlnetlabs","product":"unbound","affected":["unbound < 1.26.1"],"patched":["unbound 1.26.1"],"published":"2026-09-16","updated":"2026-09-23","sourceUpdated":"2026-09-23T19:51:14.940","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-81634","references":[{"url":"https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-81634.txt","label":"sep@nlnetlabs.nl"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-81634.json"},{"url":"https://access.redhat.com/security/cve/CVE-2026-81634"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2535054"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-81634"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-81634"},{"url":"https://access.redhat.com/errata/RHSA-2026:68590"},{"url":"https://access.redhat.com/errata/RHSA-2026:70754"},{"url":"https://access.redhat.com/errata/RHSA-2026:71419"},{"url":"https://access.redhat.com/errata/RHSA-2026:71487"}],"tags":["nvd","cve.org","csaf","vex","red-hat"],"epss":0.0048,"epssPercentile":0.41182,"ssvc":{"exploitation":"none","automatable":"yes","technicalImpact":"partial","timestamp":"2026-09-16T14:32:31.803030Z"},"ingestedAt":"2026-09-16T08:52:29.597Z","slug":"CVE-2026-81634","body":"## Overview\n\nIn 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.\n\n## Affected\n\n- `unbound < 1.26.1`\n\n## Remediation\n\nUpgrade past the affected range:\n\n- `unbound 1.26.1`\n\n## Vendor advisories\n\n- **Red Hat VEX** · Important · affected: Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7, Red Hat OpenShift Container Platform 4 · updated 2026-09-24 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-81634.json)\n- **RHSA-2026:68590** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-09-17 · [advisory](https://access.redhat.com/errata/RHSA-2026:68590)\n- **RHSA-2026:70754** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream (v. 8) · released 2026-09-23 · [advisory](https://access.redhat.com/errata/RHSA-2026:70754)\n- **RHSA-2026:71419** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream (v. 10), Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) · released 2026-09-24 · [advisory](https://access.redhat.com/errata/RHSA-2026:71419)\n- **RHSA-2026:71487** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream (v. 9), Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) · released 2026-09-24 · [advisory](https://access.redhat.com/errata/RHSA-2026:71487)","depth":"twilight","depthScore":41,"depthScoreParts":{"impact":41.3,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}