CVE-2026-56416

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{"bugzilla": {"description": "unbound: Unbound: Heap buffer overflow via malformed DNSSEC record", "id": "2506137", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2506137"}, "csaw": false, "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": "draft"}, "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."], "mitigation": {"lang": "en:us", "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."}, "name": "CVE-2026-56416", "package_state": [{"cpe": "cpe:/a:redhat:jboss_data_grid:8", "fix_state": "Fix deferred", "package_name": "unboundid-ldapsdk", "product_name": "Red Hat Data Grid 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:10", "fix_state": "Fix deferred", "package_name": "unbound", "product_name": "Red Hat Enterprise Linux 10"}, {"cpe": "cpe:/o:redhat:enterprise_linux:6", "fix_state": "Out of support scope", "package_name": "unbound", "product_name": "Red Hat Enterprise Linux 6"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Out of support scope", "package_name": "unbound", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Fix deferred", "package_name": "unbound", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Fix deferred", "package_name": "unbound", "product_name": "Red Hat Enterprise Linux 9"}, {"cpe": "cpe:/a:redhat:hummingbird:1", "fix_state": "Affected", "package_name": "unbound", "product_name": "Red Hat Hardened Images"}, {"cpe": "cpe:/a:redhat:jbosseapxp", "fix_state": "Fix deferred", "package_name": "unboundid-ldapsdk", "product_name": "Red Hat JBoss Enterprise Application Platform Expansion Pack"}, {"cpe": "cpe:/a:redhat:openshift:4", "fix_state": "Fix deferred", "package_name": "rhcos", "product_name": "Red Hat OpenShift Container Platform 4"}, {"cpe": "cpe:/a:redhat:openstack:16.2", "fix_state": "Fix deferred", "package_name": "rhosp-rhel8-tech-preview/openstack-unbound", "product_name": "Red Hat OpenStack Platform 16.2"}, {"cpe": "cpe:/a:redhat:openstack:17.1", "fix_state": "Fix deferred", "package_name": "rhosp-rhel9/openstack-unbound", "product_name": "Red Hat OpenStack Platform 17.1"}, {"cpe": "cpe:/a:redhat:openstack:18.0", "fix_state": "Fix deferred", "package_name": "rhoso/openstack-unbound-rhel9", "product_name": "Red Hat OpenStack Platform 18.0"}, {"cpe": "cpe:/a:redhat:openstack:18.0", "fix_state": "Fix deferred", "package_name": "rhoso-operators/designate-rhel9-operator", "product_name": "Red Hat OpenStack Platform 18.0"}], "public_date": "2026-07-22T13:10:24Z", "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"], "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.", "threat_severity": "Moderate"}

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