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{"bugzilla": {"description": "unbound: NLnet Labs Unbound: Denial of Service via crafted DNS glue records", "id": "2506150", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2506150"}, "csaw": false, "cvss3": {"cvss3_base_score": "5.3", "cvss3_scoring_vector": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L", "status": "draft"}, "cwe": "CWE-835", "details": ["A flaw was found in Unbound. A remote malicious actor can exploit a vulnerability by controlling a DNS delegation that returns specific glue records. This can cause Unbound to repeatedly clear its DNS caches, leading to a continuous Denial of Service (DoS) for DNS resolution."], "mitigation": {"lang": "en:us", "value": "To mitigate this issue, configure Unbound to disable the `unwanted-reply-threshold` option by setting it to `0` in the `unbound.conf` file. This prevents the cache clearing behavior triggered by malicious glue records. After modifying the configuration, restart the Unbound service for the changes to take effect."}, "name": "CVE-2026-50251", "package_state": [{"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:openshift:4", "fix_state": "Fix deferred", "package_name": "rhcos", "product_name": "Red Hat OpenShift Container Platform 4"}], "public_date": "2026-07-22T13:08:43Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2026-50251\nhttps://nvd.nist.gov/vuln/detail/CVE-2026-50251\nhttps://www.nlnetlabs.nl/downloads/unbound/CVE-2026-50251.txt"], "statement": "This Moderate flaw in Unbound allows a remote attacker to trigger a denial of service by controlling a DNS delegation. When the `unwanted-reply-threshold` option is enabled, specially crafted glue records can cause Unbound to repeatedly clear its DNS caches, disrupting DNS resolution. This occurs due to Unbound's internal handling of locally routed 0.0.0.0/::0 glue records, which are incorrectly flagged as unwanted replies.", "threat_severity": "Moderate"}

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