{"id":"UBUNTU-CVE-2026-56416","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-\u003escratch_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.","modified":"2026-08-20T23:23:39.433060450Z","published":"2026-07-22T14:17:00Z","upstream":["CVE-2026-56416"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2026-56416"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2026-56416"},{"type":"REPORT","url":"https://community.nlnetlabs.nl/t/unbound-1-25-2-released/3430"}],"affected":[{"package":{"name":"unbound","ecosystem":"Ubuntu:Pro:14.04:LTS","purl":"pkg:deb/ubuntu/unbound?arch=source&distro=esm-infra-legacy%2Ftrusty"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.4.20-1","1.4.21-1","1.4.21-1ubuntu1","1.4.21-1ubuntu2","1.4.22-1ubuntu1","1.4.22-1ubuntu2","1.4.22-1ubuntu3","1.4.22-1ubuntu4","1.4.22-1ubuntu4.14.04.1","1.4.22-1ubuntu4.14.04.2","1.4.22-1ubuntu4.14.04.3","1.4.22-1ubuntu4.14.04.3+esm1","1.4.22-1ubuntu4.14.04.3+esm2","1.4.22-1ubuntu4.14.04.3+esm3"],"ecosystem_specific":{"binaries":[{"binary_name":"libunbound2","binary_version":"1.4.22-1ubuntu4.14.04.3+esm3"},{"binary_name":"python-unbound","binary_version":"1.4.22-1ubuntu4.14.04.3+esm3"},{"binary_name":"unbound","binary_version":"1.4.22-1ubuntu4.14.04.3+esm3"},{"binary_name":"unbound-anchor","binary_version":"1.4.22-1ubuntu4.14.04.3+esm3"},{"binary_name":"unbound-host","binary_version":"1.4.22-1ubuntu4.14.04.3+esm3"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-56416.json"}},{"package":{"name":"unbound","ecosystem":"Ubuntu:Pro:16.04:LTS","purl":"pkg:deb/ubuntu/unbound?arch=source&distro=esm-infra-legacy%2Fxenial"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.4.22-1ubuntu6","1.5.7-1ubuntu1","1.5.7-1ubuntu2","1.5.8-1ubuntu1","1.5.8-1ubuntu1.1","1.5.8-1ubuntu1.1+esm1","1.5.8-1ubuntu1.1+esm2","1.5.8-1ubuntu1.1+esm3"],"ecosystem_specific":{"binaries":[{"binary_version":"1.5.8-1ubuntu1.1+esm3","binary_name":"libunbound2"},{"binary_name":"python-unbound","binary_version":"1.5.8-1ubuntu1.1+esm3"},{"binary_name":"unbound","binary_version":"1.5.8-1ubuntu1.1+esm3"},{"binary_version":"1.5.8-1ubuntu1.1+esm3","binary_name":"unbound-anchor"},{"binary_name":"unbound-host","binary_version":"1.5.8-1ubuntu1.1+esm3"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-56416.json"}},{"package":{"name":"unbound","ecosystem":"Ubuntu:Pro:18.04:LTS","purl":"pkg:deb/ubuntu/unbound?arch=source&distro=esm-infra%2Fbionic"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.6.5-1","1.6.7-1","1.6.7-1build1","1.6.7-1ubuntu1","1.6.7-1ubuntu2","1.6.7-1ubuntu2.1","1.6.7-1ubuntu2.2","1.6.7-1ubuntu2.3","1.6.7-1ubuntu2.4","1.6.7-1ubuntu2.5","1.6.7-1ubuntu2.6","1.6.7-1ubuntu2.6+esm2","1.6.7-1ubuntu2.6+esm3","1.6.7-1ubuntu2.6+esm4"],"ecosystem_specific":{"binaries":[{"binary_name":"libunbound2","binary_version":"1.6.7-1ubuntu2.6+esm4"},{"binary_name":"python-unbound","binary_version":"1.6.7-1ubuntu2.6+esm4"},{"binary_name":"python3-unbound","binary_version":"1.6.7-1ubuntu2.6+esm4"},{"binary_version":"1.6.7-1ubuntu2.6+esm4","binary_name":"unbound"},{"binary_name":"unbound-anchor","binary_version":"1.6.7-1ubuntu2.6+esm4"},{"binary_version":"1.6.7-1ubuntu2.6+esm4","binary_name":"unbound-host"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-56416.json"}},{"package":{"name":"unbound","ecosystem":"Ubuntu:Pro:20.04:LTS","purl":"pkg:deb/ubuntu/unbound?arch=source&distro=esm-infra%2Ffocal"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.9.0-2ubuntu1","1.9.0-2ubuntu2","1.9.4-2","1.9.4-2ubuntu1","1.9.4-2ubuntu1.1","1.9.4-2ubuntu1.2","1.9.4-2ubuntu1.3","1.9.4-2ubuntu1.4","1.9.4-2ubuntu1.5","1.9.4-2ubuntu1.6","1.9.4-2ubuntu1.8","1.9.4-2ubuntu1.9","1.9.4-2ubuntu1.11","1.9.4-2ubuntu1.11+esm1"],"ecosystem_specific":{"binaries":[{"binary_version":"1.9.4-2ubuntu1.11+esm1","binary_name":"libunbound8"},{"binary_version":"1.9.4-2ubuntu1.11+esm1","binary_name":"python-unbound"},{"binary_name":"python3-unbound","binary_version":"1.9.4-2ubuntu1.11+esm1"},{"binary_name":"unbound","binary_version":"1.9.4-2ubuntu1.11+esm1"},{"binary_name":"unbound-anchor","binary_version":"1.9.4-2ubuntu1.11+esm1"},{"binary_version":"1.9.4-2ubuntu1.11+esm1","binary_name":"unbound-host"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-56416.json"}},{"package":{"name":"unbound","ecosystem":"Ubuntu:22.04:LTS","purl":"pkg:deb/ubuntu/unbound?arch=source&distro=jammy"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.13.1-1ubuntu1","1.13.1-1ubuntu3","1.13.1-1ubuntu5","1.13.1-1ubuntu5.1","1.13.1-1ubuntu5.2","1.13.1-1ubuntu5.3","1.13.1-1ubuntu5.4","1.13.1-1ubuntu5.5","1.13.1-1ubuntu5.7","1.13.1-1ubuntu5.8","1.13.1-1ubuntu5.10","1.13.1-1ubuntu5.11","1.13.1-1ubuntu5.12","1.13.1-1ubuntu5.13","1.13.1-1ubuntu5.14","1.13.1-1ubuntu5.15"],"ecosystem_specific":{"binaries":[{"binary_name":"libunbound8","binary_version":"1.13.1-1ubuntu5.15"},{"binary_version":"1.13.1-1ubuntu5.15","binary_name":"python3-unbound"},{"binary_name":"unbound","binary_version":"1.13.1-1ubuntu5.15"},{"binary_version":"1.13.1-1ubuntu5.15","binary_name":"unbound-anchor"},{"binary_name":"unbound-host","binary_version":"1.13.1-1ubuntu5.15"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-56416.json"}},{"package":{"name":"unbound","ecosystem":"Ubuntu:24.04:LTS","purl":"pkg:deb/ubuntu/unbound?arch=source&distro=noble"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.17.1-2","1.18.0-2ubuntu1","1.18.0-2ubuntu2","1.19.1-1ubuntu1","1.19.2-1ubuntu1","1.19.2-1ubuntu3","1.19.2-1ubuntu3.1","1.19.2-1ubuntu3.2","1.19.2-1ubuntu3.3","1.19.2-1ubuntu3.4","1.19.2-1ubuntu3.5","1.19.2-1ubuntu3.6","1.19.2-1ubuntu3.7","1.19.2-1ubuntu3.8","1.19.2-1ubuntu3.9"],"ecosystem_specific":{"binaries":[{"binary_name":"libunbound8","binary_version":"1.19.2-1ubuntu3.9"},{"binary_name":"python3-unbound","binary_version":"1.19.2-1ubuntu3.9"},{"binary_version":"1.19.2-1ubuntu3.9","binary_name":"unbound"},{"binary_version":"1.19.2-1ubuntu3.9","binary_name":"unbound-anchor"},{"binary_name":"unbound-host","binary_version":"1.19.2-1ubuntu3.9"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-56416.json"}},{"package":{"name":"unbound","ecosystem":"Ubuntu:26.04:LTS","purl":"pkg:deb/ubuntu/unbound?arch=source&distro=resolute"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.22.0-2ubuntu2","1.22.0-2ubuntu4","1.24.2-1ubuntu1","1.24.2-1ubuntu2","1.24.2-1ubuntu2.1","1.24.2-1ubuntu2.2"],"ecosystem_specific":{"binaries":[{"binary_name":"libunbound8","binary_version":"1.24.2-1ubuntu2.2"},{"binary_name":"python3-unbound","binary_version":"1.24.2-1ubuntu2.2"},{"binary_name":"unbound","binary_version":"1.24.2-1ubuntu2.2"},{"binary_version":"1.24.2-1ubuntu2.2","binary_name":"unbound-anchor"},{"binary_version":"1.24.2-1ubuntu2.2","binary_name":"unbound-host"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-56416.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L"},{"type":"Ubuntu","score":"medium"}]}