{"id":"UBUNTU-CVE-2025-5994","details":"A multi-vendor cache poisoning vulnerability named 'Rebirthday Attack' has been discovered in caching resolvers that support EDNS Client Subnet (ECS). Unbound is also vulnerable when compiled with ECS support, i.e., '--enable-subnet', AND configured to send ECS information along with queries to upstream name servers, i.e., at least one of the 'send-client-subnet', 'client-subnet-zone' or 'client-subnet-always-forward' options is used. Resolvers supporting ECS need to segregate outgoing queries to accommodate for different outgoing ECS information. This re-opens up resolvers to a birthday paradox attack (Rebirthday Attack) that tries to match the DNS transaction ID in order to cache non-ECS poisonous replies.","modified":"2026-06-02T20:15:05.974465609Z","published":"2025-07-17T00:00:00Z","related":["USN-7666-1"],"upstream":["CVE-2025-5994"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2025-5994"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2025-5994"},{"type":"REPORT","url":"https://nlnetlabs.nl/downloads/unbound/CVE-2025-5994.txt"},{"type":"ADVISORY","url":"https://ubuntu.com/security/notices/USN-7666-1"}],"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_version":"1.4.22-1ubuntu4.14.04.3+esm3","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"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2025/UBUNTU-CVE-2025-5994.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_version":"1.5.8-1ubuntu1.1+esm3","binary_name":"python-unbound"},{"binary_version":"1.5.8-1ubuntu1.1+esm3","binary_name":"unbound"},{"binary_version":"1.5.8-1ubuntu1.1+esm3","binary_name":"unbound-anchor"},{"binary_version":"1.5.8-1ubuntu1.1+esm3","binary_name":"unbound-host"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2025/UBUNTU-CVE-2025-5994.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_version":"1.6.7-1ubuntu2.6+esm4","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_name":"unbound"},{"binary_version":"1.6.7-1ubuntu2.6+esm4","binary_name":"unbound-anchor"},{"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/2025/UBUNTU-CVE-2025-5994.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_version":"1.9.4-2ubuntu1.11+esm1","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_name":"unbound-host"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2025/UBUNTU-CVE-2025-5994.json"}},{"package":{"name":"unbound","ecosystem":"Ubuntu:22.04:LTS","purl":"pkg:deb/ubuntu/unbound?arch=source&distro=jammy"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.13.1-1ubuntu5.11"}]}],"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"],"ecosystem_specific":{"binaries":[{"binary_version":"1.13.1-1ubuntu5.11","binary_name":"libunbound8"},{"binary_version":"1.13.1-1ubuntu5.11","binary_name":"python3-unbound"},{"binary_version":"1.13.1-1ubuntu5.11","binary_name":"unbound"},{"binary_version":"1.13.1-1ubuntu5.11","binary_name":"unbound-anchor"},{"binary_version":"1.13.1-1ubuntu5.11","binary_name":"unbound-host"}],"availability":"No subscription required"},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2025/UBUNTU-CVE-2025-5994.json"}},{"package":{"name":"unbound","ecosystem":"Ubuntu:24.04:LTS","purl":"pkg:deb/ubuntu/unbound?arch=source&distro=noble"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.19.2-1ubuntu3.5"}]}],"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"],"ecosystem_specific":{"binaries":[{"binary_version":"1.19.2-1ubuntu3.5","binary_name":"libunbound8"},{"binary_version":"1.19.2-1ubuntu3.5","binary_name":"python3-unbound"},{"binary_version":"1.19.2-1ubuntu3.5","binary_name":"unbound"},{"binary_version":"1.19.2-1ubuntu3.5","binary_name":"unbound-anchor"},{"binary_version":"1.19.2-1ubuntu3.5","binary_name":"unbound-host"}],"availability":"No subscription required"},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2025/UBUNTU-CVE-2025-5994.json"}},{"package":{"name":"unbound","ecosystem":"Ubuntu:25.10","purl":"pkg:deb/ubuntu/unbound?arch=source&distro=questing"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.22.0-2ubuntu1"}]}],"versions":["1.22.0-1ubuntu1"],"ecosystem_specific":{"binaries":[{"binary_version":"1.22.0-2ubuntu1","binary_name":"libunbound8"},{"binary_version":"1.22.0-2ubuntu1","binary_name":"python3-unbound"},{"binary_version":"1.22.0-2ubuntu1","binary_name":"unbound"},{"binary_version":"1.22.0-2ubuntu1","binary_name":"unbound-anchor"},{"binary_version":"1.22.0-2ubuntu1","binary_name":"unbound-host"}],"availability":"No subscription required"},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2025/UBUNTU-CVE-2025-5994.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/R:U/V:C"},{"type":"Ubuntu","score":"medium"}]}