Unbound Cache poisoning
CVE: CVE-2025-5994
Component: unbound
CWE: CWE-349
Severity: Important
CVSS v3: 7.5/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Release date: 2025-07-16T14:38:22.738000+00:00

A cache poisoning flaw was found in Unbound. Resolvers supporting EDNS Client Subnet (ECS) must segregate outgoing queries to accommodate different outgoing ECS information. This issue reopens resolvers to a birthday paradox attack, known as the Rebirthday Attack, which attempts to match the DNS transaction ID with cache non-ECS poisoned replies.

Statement: This vulnerability is considered Important rather than Moderate because it directly compromises the integrity of DNS caching mechanisms in resolvers supporting EDNS Client Subnet (ECS). The flaw allows an attacker to exploit the birthday paradox by generating a high volume of concurrent queries with different ECS values, thereby increasing the chance of a transaction ID collision with a spoofed response. If the resolver fails to properly segregate cache entries by ECS scope, it may accept and cache a malicious non-ECS response, effectively leading to DNS cache poisoning. Unlike typical poisoning attempts that require precise timing or privileged network positions, this attack can be carried out remotely with a high success rate, especially in resolvers that do not correctly isolate ECS queries.

Remediation:
For OpenShift Container Platform 4.12 see the following documentation, which will be updated shortly for this release, for important instructions on how to upgrade your cluster and fully apply this asynchronous errata update:

https://docs.redhat.com/en/documentation/openshift_container_platform/4.12/html/release_notes

You may download the oc tool and use it to inspect release image metadata for x86_64, s390x, ppc64le, and aarch64 architectures. The image digests may be found at https://quay.io/repository/openshift-release-dev/ocp-release?tab=tags.

              The sha value for the release is as follows:

              (For x86_64 architecture)
              The image digest is sha256:d26fd3fd30ac6ae13f2779045d4e2defbf77aa24db5393d91df19488fd42504d

All OpenShift Container Platform 4.12 users are advised to upgrade to these updated packages and images when they are available in the appropriate release channel. To check for available updates, use the OpenShift CLI (oc) or web console. Instructions for upgrading a cluster are available at https://docs.redhat.com/en/documentation/openshift_container_platform/4.12/html-single/updating_clusters/index#updating-cluster-within-minor.
For OpenShift Container Platform 4.13 see the following documentation, which will be updated shortly for this release, for important instructions on how to upgrade your cluster and fully apply this asynchronous errata update:

https://docs.redhat.com/en/documentation/openshift_container_platform/4.13/html/release_notes

You may download the oc tool and use it to inspect release image metadata for x86_64, s390x, ppc64le, and aarch64 architectures. The image digests may be found at https://quay.io/repository/openshift-release-dev/ocp-release?tab=tags.

      The sha values for the release are as follows:

      (For x86_64 architecture)
      The image digest is {x86_64_DIGEST}

      (For s390x architecture)
      The image digest is {s390x_DIGEST}

      (For ppc64le architecture)
      The image digest is {ppc64le_DIGEST}

      (For aarch64 architecture)
      The image digest is {aarch64_DIGEST}

All OpenShift Container Platform 4.13 users are advised to upgrade to these updated packages and images when they are available in the appropriate release channel. To check for available updates, use the OpenShift CLI (oc) or web console. Instructions for upgrading a cluster are available at https://docs.redhat.com/en/documentation/openshift_container_platform/4.13/html-single/updating_clusters/index#updating-cluster-within-minor.
For OpenShift Container Platform 4.14 see the following documentation,
which will be updated shortly for this release, for important instructions
on how to upgrade your cluster and fully apply this asynchronous errata
update:

https://docs.redhat.com/en/documentation/openshift_container_platform/4.14/html/release_notes/

You may download the oc tool and use it to inspect release image metadata
for x86_64, s390x, ppc64le, and aarch64 architectures. The image digests
may be found at
https://quay.io/repository/openshift-release-dev/ocp-release?tab=tags.

The sha values for the release are as follows:

      (For x86_64 architecture)
      The image digest is {x864_DIGEST}

      (For s390x architecture)
      The image digest is {s390x_DIGEST}

      (For ppc64le architecture)
      The image digest is {ppc64le_DIGEST}

      (For aarch64 architecture)
      The image digest is {aarch64_DIGEST}

All OpenShift Container Platform 4.14 users are advised to upgrade to these
updated packages and images when they are available in the appropriate
release channel. To check for available updates, use the OpenShift CLI (oc)
or web console. Instructions for upgrading a cluster are available at
https://docs.redhat.com/en/documentation/openshift_container_platform/4.14/html-single/updating_clusters/index#updating-cluster-cli.
For OpenShift Container Platform 4.17 see the following documentation,
which will be updated shortly for this release, for important instructions
on how to upgrade your cluster and fully apply this asynchronous errata
update:

https://docs.redhat.com/en/documentation/openshift_container_platform/4.17/html/release_notes/

You may download the oc tool and use it to inspect release image metadata
for x86_64, s390x, ppc64le, and aarch64 architectures. The image digests
may be found at
https://quay.io/repository/openshift-release-dev/ocp-release?tab=tags.

The sha values for the release are as follows:

      (For x86_64 architecture)
      The image digest is {x864_DIGEST}

      (For s390x architecture)
      The image digest is {s390x_DIGEST}

      (For ppc64le architecture)
      The image digest is {ppc64le_DIGEST}

      (For aarch64 architecture)
      The image digest is {aarch64_DIGEST}

All OpenShift Container Platform 4.17 users are advised to upgrade to these
updated packages and images when they are available in the appropriate
release channel. To check for available updates, use the OpenShift CLI (oc)
or web console. Instructions for upgrading a cluster are available at
https://docs.redhat.com/en/documentation/openshift_container_platform/4.17/html-single/updating_clusters/index#updating-cluster-cli.
For OpenShift Container Platform 4.18 see the following documentation, which will be updated shortly for this release, for important instructions on how to upgrade your cluster and fully apply this asynchronous errata update:

https://docs.redhat.com/en/documentation/openshift_container_platform/4.18/html/release_notes/

You may download the oc tool and use it to inspect release image metadata for x86_64, s390x, ppc64le, and aarch64 architectures. The image digests may be found at https://quay.io/repository/openshift-release-dev/ocp-release?tab=tags.

The sha values for the release are as follows:

      (For x86_64 architecture)
      The image digest is {x864_DIGEST}

      (For s390x architecture)
      The image digest is {s390x_DIGEST}

      (For ppc64le architecture)
      The image digest is {ppc64le_DIGEST}

      (For aarch64 architecture)
      The image digest is {aarch64_DIGEST}

All OpenShift Container Platform 4.18 users are advised to upgrade to these updated packages and images when they are available in the appropriate release channel. To check for available updates, use the OpenShift CLI (oc) or web console. Instructions for upgrading a cluster are available at https://docs.redhat.com/en/documentation/openshift_container_platform/4.18/html-single/updating_clusters/index#updating-cluster-cli.
For OpenShift Container Platform 4.19 see the following documentation, which will be updated shortly for this release, for important instructions on how to upgrade your cluster and fully apply this asynchronous errata update:

https://docs.redhat.com/en/documentation/openshift_container_platform/4.19/html/release_notes/

You may download the oc tool and use it to inspect release image metadata for x86_64, s390x, ppc64le, and aarch64 architectures. The image digests may be found at https://quay.io/repository/openshift-release-dev/ocp-release?tab=tags.

The sha values for the release are as follows:

      (For x86_64 architecture)
      The image digest is {x864_DIGEST}

      (For s390x architecture)
      The image digest is {s390x_DIGEST}

      (For ppc64le architecture)
      The image digest is {ppc64le_DIGEST}

      (For aarch64 architecture)
      The image digest is {aarch64_DIGEST}

All OpenShift Container Platform 4.19 users are advised to upgrade to these updated packages and images when they are available in the appropriate release channel. To check for available updates, use the OpenShift CLI (oc) or web console. Instructions for upgrading a cluster are available at https://docs.redhat.com/en/documentation/openshift_container_platform/4.19/html-single/updating_clusters/index#updating-cluster-cli.
For OpenShift Container Platform 4.20 see the following documentation, which will be updated shortly for this release, for important instructions on how to upgrade your cluster and fully apply this asynchronous errata update:

https://docs.redhat.com/en/documentation/openshift_container_platform/4.20/html/release_notes/

You may download the oc tool and use it to inspect release image metadata for x86_64, s390x, ppc64le, and aarch64 architectures. The image digests may be found at https://quay.io/repository/openshift-release-dev/ocp-release?tab=tags.

The sha values for the release are as follows:

      (For x86_64 architecture)
      The image digest is sha256:d1dc76522d1e235b97675b28e977cb8c452f47d39c0eb519cde02114925f91d2

      (For s390x architecture)
      The image digest is sha256:bb2b07ca992b8c976341c145ccdcefbd57e946a590efaa5e10d60fc5a2cbe503

      (For ppc64le architecture)
      The image digest is sha256:678369ac0a189674b3d9f5779ee7042b39e625ee580579ec302d8899f8ddc613

      (For aarch64 architecture)
      The image digest is sha256:791079aeb081a9193cec139ba4dccbafbfc9437b6e5e39d70225b0e6d2f51b34

All OpenShift Container Platform 4.20 users are advised to upgrade to these updated packages and images when they are available in the appropriate release channel. To check for available updates, use the OpenShift CLI (oc) or web console. Instructions for upgrading a cluster are available at https://docs.redhat.com/en/documentation/openshift_container_platform/4.20/html-single/updating_clusters/index#updating-cluster-cli.
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.