{
  "threat_severity" : "Moderate",
  "public_date" : "2026-07-22T13:08:54Z",
  "bugzilla" : {
    "description" : "unbound: Unbound: DNS cache poisoning via UDP source port predictability",
    "id" : "2506133",
    "url" : "https://bugzilla.redhat.com/show_bug.cgi?id=2506133"
  },
  "cvss3" : {
    "cvss3_base_score" : "6.5",
    "cvss3_scoring_vector" : "CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
    "status" : "verified"
  },
  "cwe" : "CWE-349",
  "details" : [ "In NLnet Labs Unbound 1.4.22 up to and including 1.25.1, UDP source port is randomized and intended to serve as a secret value that increases the entropy of DNS transactions. When resolver load balancing policies depend on the source port while their outcome is revealed this secrecy is undermined. The vulnerability arises when the load balancing policy is consistent with respect to the incoming source UDP port and IP address while heavily depending on the incoming source UDP port as a randomization source. When the SO_REUSEPORT configuration option is enabled ('so-reuseport: yes') in Unbound (by default), it meets these conditions, making it vulnerable for DNS cache poisoning attacks. Upon startup, Unbound randomly partitions the available UDP source port space into disjoint subsets of (almost) equal size, assigning each subset to a specific worker thread. When an incoming DNS query is received, the kernel’s SO_REUSEPORT load balancing mechanism deterministically assigns the query to a socket associated with a particular thread. All outgoing DNS queries generated during the resolution of that request use source ports selected exclusively from the port subset assigned to the corresponding thread. Since these port subsets are disjoint across threads, the source port observed in a resolver’s outgoing query to an authoritative name server serves as a reliable indicator of the worker thread that processed the original client query. A malicious actor can acquire the mapping between incoming UDP source ports (for a given fixed source IP address) and Unbound worker threads and leverage it to conduct DNS cache poisoning attacks by effectively lowering the random port population per thread.", "A flaw in Unbound's SO_REUSEPORT implementation reduces UDP source port entropy by allowing attackers to map ports to specific worker threads. This enables DNS cache poisoning, potentially leading to traffic redirection or unauthorized information disclosure." ],
  "statement" : "Moderate: This flaw allows for DNS cache poisoning due to predictable UDP source ports when Unbound's `so-reuseport` option is enabled by default. An attacker on an adjacent network can exploit this to compromise the integrity of DNS resolutions, leading to potential redirection of traffic.",
  "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" : "Affected",
    "package_name" : "unbound",
    "cpe" : "cpe:/o:redhat:enterprise_linux:10"
  }, {
    "product_name" : "Red Hat Enterprise Linux 6",
    "fix_state" : "Not affected",
    "package_name" : "unbound",
    "cpe" : "cpe:/o:redhat:enterprise_linux:6"
  }, {
    "product_name" : "Red Hat Enterprise Linux 7",
    "fix_state" : "Affected",
    "package_name" : "unbound",
    "cpe" : "cpe:/o:redhat:enterprise_linux:7"
  }, {
    "product_name" : "Red Hat Enterprise Linux 8",
    "fix_state" : "Affected",
    "package_name" : "unbound",
    "cpe" : "cpe:/o:redhat:enterprise_linux:8"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9",
    "fix_state" : "Affected",
    "package_name" : "unbound",
    "cpe" : "cpe:/o:redhat:enterprise_linux:9"
  }, {
    "product_name" : "Red Hat OpenShift Container Platform 4",
    "fix_state" : "Affected",
    "package_name" : "openshift/ose-rhel-coreos-8",
    "cpe" : "cpe:/a:redhat:openshift:4"
  }, {
    "product_name" : "Red Hat OpenShift Container Platform 4",
    "fix_state" : "Affected",
    "package_name" : "openshift/ose-rhel-coreos-9",
    "cpe" : "cpe:/a:redhat:openshift:4"
  } ],
  "references" : [ "https://www.cve.org/CVERecord?id=CVE-2026-50252\nhttps://nvd.nist.gov/vuln/detail/CVE-2026-50252\nhttps://www.nlnetlabs.nl/downloads/unbound/CVE-2026-50252.txt" ],
  "name" : "CVE-2026-50252",
  "mitigation" : {
    "value" : "Disable the so-reuseport option by explicitly setting so-reuseport: no in your unbound.conf file. This prevents the deterministic mapping of worker threads to outbound UDP source ports, effectively stopping the cache poisoning vector. Additionally, restrict who can query the resolver using the access-control directive to reduce the overall attack surface, and restart the Unbound service to apply the changes.",
    "lang" : "en:us"
  },
  "csaw" : false
}