{
  "threat_severity" : "Low",
  "public_date" : "2026-07-22T13:06:42Z",
  "bugzilla" : {
    "description" : "unbound: Unbound: Denial of Service due to 'harden-below-nxdomain' logic bypass",
    "id" : "2506130",
    "url" : "https://bugzilla.redhat.com/show_bug.cgi?id=2506130"
  },
  "cvss3" : {
    "cvss3_base_score" : "3.7",
    "cvss3_scoring_vector" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L",
    "status" : "verified"
  },
  "cwe" : "CWE-193",
  "details" : [ "In NLnet Labs Unbound 1.13.2 up to and including 1.25.1, stub or forward zones where the name is below an intermediate labed below a DNSSEC signed zone could be shadowed by the intermediate label's secure NXDOMAIN answer from the parent. This is caused by an off-by-one error in 'harden-below-nxdomain' logic; enabled by default. It effectively bypasses the configuration and the configured stub/forward zone is never contacted. 'harden-below-nxdomain' does an upward DNS cache walk together with a delegation point guard that does not allow NXDOMAIN synthesis above stub/forward zones. The guard tests the domain name but before stripping a label. This results in an iteration where the domain name equals the configured stub/forward zone apex that passes the guard, strips one more label, and probes the cache at the apex's immediate public parent. If that parent has a cached DNSSEC-secure NXDOMAIN, which it will for any private namespace nested two or more labels under a signed public name, the walk returns it and the configured stub/forward upstream is never contacted. This can only be triggered by the query for the intermediate label (between the stub/forward apex and the DNSSEC parent zone).", "An off-by-one error in Unbound's default harden-below-nxdomain logic can lead to a denial of service. When an intermediate label under a DNSSEC-signed zone is queried, the flaw incorrectly bypasses configured stub or forward zones, disrupting their name resolution." ],
  "statement" : "Low impact. This vulnerability in Unbound's `harden-below-nxdomain` logic, enabled by default in Red Hat products, can lead to a denial of service. Exploitation requires a specific configuration of stub or forward zones below a DNSSEC-signed zone and a targeted query for an intermediate label, making the attack complex and limiting its overall impact.",
  "affected_release" : [ {
    "product_name" : "Red Hat Hardened Images",
    "release_date" : "2026-07-22T00:00:00Z",
    "advisory" : "RHSA-2026:43588",
    "cpe" : "cpe:/a:redhat:hummingbird:1",
    "package" : "unbound-main-1.25.2-0.1.hum1"
  } ],
  "package_state" : [ {
    "product_name" : "Red Hat Enterprise Linux 10",
    "fix_state" : "Fix deferred",
    "package_name" : "unbound",
    "cpe" : "cpe:/o:redhat:enterprise_linux:10"
  }, {
    "product_name" : "Red Hat Enterprise Linux 6",
    "fix_state" : "Not affected",
    "package_name" : "unbound",
    "cpe" : "cpe:/o:redhat:enterprise_linux:6"
  }, {
    "product_name" : "Red Hat Enterprise Linux 7",
    "fix_state" : "Not affected",
    "package_name" : "unbound",
    "cpe" : "cpe:/o:redhat:enterprise_linux:7"
  }, {
    "product_name" : "Red Hat Enterprise Linux 8",
    "fix_state" : "Fix deferred",
    "package_name" : "unbound",
    "cpe" : "cpe:/o:redhat:enterprise_linux:8"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9",
    "fix_state" : "Fix deferred",
    "package_name" : "unbound",
    "cpe" : "cpe:/o:redhat:enterprise_linux:9"
  }, {
    "product_name" : "Red Hat OpenShift Container Platform 4",
    "fix_state" : "Not affected",
    "package_name" : "openshift/ose-rhel-coreos-8",
    "cpe" : "cpe:/a:redhat:openshift:4"
  }, {
    "product_name" : "Red Hat OpenShift Container Platform 4",
    "fix_state" : "Fix deferred",
    "package_name" : "openshift/ose-rhel-coreos-9",
    "cpe" : "cpe:/a:redhat:openshift:4"
  } ],
  "references" : [ "https://www.cve.org/CVERecord?id=CVE-2026-44687\nhttps://nvd.nist.gov/vuln/detail/CVE-2026-44687\nhttps://www.nlnetlabs.nl/downloads/unbound/CVE-2026-44687.txt" ],
  "name" : "CVE-2026-44687",
  "mitigation" : {
    "value" : "Disable the harden-below-nxdomain option in the Unbound configuration to prevent the logic bypass that leads to the denial of service. Note that disabling this option may reduce the overall DNSSEC hardening provided by Unbound.\nEdit /etc/unbound/unbound.conf and set the following in the server: section:\nharden-below-nxdomain: no\nRestart the Unbound service for the changes to take effect:\nsystemctl restart unbound\nWarning: Restarting the Unbound service will temporarily interrupt local DNS resolution.",
    "lang" : "en:us"
  },
  "csaw" : false
}