{
  "threat_severity" : "Low",
  "public_date" : "2026-07-22T13:04:52Z",
  "bugzilla" : {
    "description" : "unbound: Unbound: Denial of Service via terminated DNS-over-QUIC queries",
    "id" : "2506143",
    "url" : "https://bugzilla.redhat.com/show_bug.cgi?id=2506143"
  },
  "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-911",
  "details" : [ "In NLnet Labs Unbound 1.22.0 up to and including 1.25.1, client terminated DNS-over-QUIC (DoQ) queries are not accounted properly by Unbound resulting in low-cost inflation of the waiting number of replies for already in-flight resolution queries. This results in degradation of resolution service for new clients for already in-flight queries. A malicious actor can exploit the vulnerability by issuing DoQ queries for query names that need resolution and proceeding on immediately terminating the query by one of STOP_SENDING/RESET_STREAM/CONNECTION_CLOSE QUIC frames. Those terminated DoQ queries are not properly counted for and keep inflating the number of waiting replies for in-flight queries. When the maximum is reached, it results in silent query drops for new clients needing resolution for already in-flight queries. This vulnerability needs Unbound to be compiled with DoQ support ('--with-libngtcp2') and the 'quic-port' to be configured for the listening interfaces. Additionally, a malicious actor needs access to multiple source IPs to bypass the by-default configured 'wait-limit' option.", "A flaw was found in Unbound, a Domain Name System (DNS) resolver. A remote attacker can exploit this vulnerability by sending and immediately terminating DNS-over-QUIC (DoQ) queries. This improper handling of terminated queries can lead to a build-up of pending responses, causing a degradation of service for new clients and ultimately a Denial of Service (DoS)." ],
  "statement" : "This vulnerability is rated as Low impact. Unbound, as distributed in Red Hat products, is not typically configured with DNS-over-QUIC (DoQ) support enabled by default. Exploitation requires Unbound to be explicitly compiled with `--with-libngtcp2` and have `quic-port` configured, in addition to an attacker bypassing default rate limits with multiple source IPs. This makes successful exploitation difficult in standard Red Hat deployments.",
  "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" : "Not affected",
    "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" : "Fix deferred",
    "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-2026-41637\nhttps://nvd.nist.gov/vuln/detail/CVE-2026-41637\nhttps://www.nlnetlabs.nl/downloads/unbound/CVE-2026-41637.txt" ],
  "name" : "CVE-2026-41637",
  "mitigation" : {
    "value" : "To mitigate this issue, completely disable DNS-over-QUIC (DoQ) support by removing or commenting out the quic-port directive in your Unbound configuration.\nRestart the Unbound service to apply the changes and clear any lingering resource limits.",
    "lang" : "en:us"
  },
  "csaw" : false
}