{
  "threat_severity" : "Moderate",
  "public_date" : "2026-07-22T13:10:24Z",
  "bugzilla" : {
    "description" : "unbound: Unbound: Heap buffer overflow via malformed DNSSEC record",
    "id" : "2506137",
    "url" : "https://bugzilla.redhat.com/show_bug.cgi?id=2506137"
  },
  "cvss3" : {
    "cvss3_base_score" : "4.8",
    "cvss3_scoring_vector" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L",
    "status" : "verified"
  },
  "cwe" : "CWE-125",
  "details" : [ "In NLnet Labs Unbound up to and including version 1.25.1, when the validator builds the canonical RDATA form for an RRSIG-covered PX/RP/MINFO/SOA RRset, it computes the address of the second embedded domain name as 'datstart + dname_valid(datstart, ...)' and passes it straight to 'query_dname_tolower()' without checking that a second name is actually present in the RDATA. The wire-format parser accepts multi-dname RRs whose RDATA ends after the first name, so an attacker who runs a DNSSEC-signed authoritative server can deliver a record with an absent second domain name (e.g. SOA record) and cause 'query_dname_tolower()' to walk label-by-label through stale bytes in the per-worker 'env->scratch_buffer', past the end of that heap allocation if 'msg-buffer-size' has been lowered from the default. This leads to heap buffer overflow and on a release build the outcome relies heavily on the contents of the buffer tail and the adjacent heap chunk.", "A vulnerability in Unbound allows remote attackers using malicious DNSSEC-signed servers to send malformed records that trigger a heap buffer overflow. This can cause a denial of service or potential limited information disclosure." ],
  "statement" : "This Moderate impact flaw in Unbound allows a remote attacker to trigger a heap buffer overflow by providing specially crafted DNSSEC records from a malicious authoritative server. This can lead to a denial of service for the Unbound service or potentially limited information disclosure. Exploitation requires the Unbound DNSSEC validator to process malformed records, which may be exacerbated if `msg-buffer-size` is configured below its default value.",
  "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" : "Out of support scope",
    "package_name" : "unbound",
    "cpe" : "cpe:/o:redhat:enterprise_linux:6"
  }, {
    "product_name" : "Red Hat Enterprise Linux 7",
    "fix_state" : "Out of support scope",
    "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" : "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-2026-56416\nhttps://nvd.nist.gov/vuln/detail/CVE-2026-56416\nhttps://www.nlnetlabs.nl/downloads/unbound/CVE-2026-56416.txt" ],
  "name" : "CVE-2026-56416",
  "mitigation" : {
    "value" : "To mitigate this issue, consider disabling DNSSEC validation in Unbound if it is not strictly required for your environment. This can be achieved by ensuring `module-config: \"iterator\"` is used in `unbound.conf` and that no `trust-anchor` or `auto-trust-anchor-file` directives are present. Disabling DNSSEC validation will reduce the security assurances provided by DNSSEC. Alternatively, configure Unbound to only perform DNSSEC validation for trusted zones. A restart of the Unbound service is required for changes to take effect.",
    "lang" : "en:us"
  },
  "csaw" : false
}