UBUNTU-CVE-2026-50251

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Source

https://ubuntu.com/security/CVE-2026-50251

Import Source

https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-50251.json

JSON Data

https://api.osv.dev/v1/vulns/UBUNTU-CVE-2026-50251

Upstream

CVE-2026-50251

Published

2026-07-22T14:17:00Z

Modified

2026-08-20T23:24:40Z

Severity

5.3 (Medium) CVSS_V3 - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L CVSS Calculator
Ubuntu - medium

Summary

[none]

Details

In NLnet Labs Unbound up to and including version 1.25.1, when 'unwanted-reply-threshold' is enabled (set to any value greater than zero), glue records of 0.0.0.0/::0 can short-circuit Unbound, on systems that can direct such traffic, by issuing DNS queries and receiving seemingly unwanted replies since the remote IP does not match the original source IP of 0.0.0.0/::0. This behavior keeps on looping for the glue records and pushing the counter to the configured 'unwanted-reply-threshold' that triggers a defensive cache clear. A malicious actor who controls a delegation that returns in-bailiwick glue of 0.0.0.0/::0 can drive the counter to the limit of 'unwanted-reply-threshold' to the threshold and trigger a cache clean of the message and rrset caches; at will, indefinitely, without sending a single spoofed packet. The iterator uses the 0.0.0.0/::0 glue, and a system that can route this (e.g., Linux kernel routes the datagram over loopback), Unbound's own listener answers from 127.0.0.1. Because of the mismatch of 0.0.0.0 and 127.0.0.1, in this example, Unbound accounts the reply as an unwanted (probably spoofed) answer. The counter resets to zero on every cache flush, so the attack loops forever.

References

Affected packages

Ubuntu:22.04:LTS

unbound

Package

Name: unbound
Purl: pkg:deb/ubuntu/unbound?arch=source&distro=jammy

Affected ranges

Type: ECOSYSTEM
Events: Introduced

0 Unknown introduced version / All previous versions are affected

Affected versions

1.*

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_name": "python3-unbound",
            "binary_version": "1.13.1-1ubuntu5.15"
        },
        {
            "binary_name": "unbound",
            "binary_version": "1.13.1-1ubuntu5.15"
        },
        {
            "binary_name": "unbound-anchor",
            "binary_version": "1.13.1-1ubuntu5.15"
        },
        {
            "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-2026-50251.json"

Ubuntu:24.04:LTS

unbound

Package

Name: unbound
Purl: pkg:deb/ubuntu/unbound?arch=source&distro=noble

Affected ranges

Type: ECOSYSTEM
Events: Introduced

0 Unknown introduced version / All previous versions are affected

Affected versions

1.*

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_name": "unbound",
            "binary_version": "1.19.2-1ubuntu3.9"
        },
        {
            "binary_name": "unbound-anchor",
            "binary_version": "1.19.2-1ubuntu3.9"
        },
        {
            "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-2026-50251.json"

Ubuntu:26.04:LTS

unbound

Package

Name: unbound
Purl: pkg:deb/ubuntu/unbound?arch=source&distro=resolute

Affected ranges

Type: ECOSYSTEM
Events: Introduced

0 Unknown introduced version / All previous versions are affected

Affected versions

1.*

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_name": "unbound-anchor",
            "binary_version": "1.24.2-1ubuntu2.2"
        },
        {
            "binary_name": "unbound-host",
            "binary_version": "1.24.2-1ubuntu2.2"
        }
    ]
}

Database specific

source

"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-50251.json"

Ubuntu:Pro:14.04:LTS

unbound

Package

Name: unbound
Purl: pkg:deb/ubuntu/unbound?arch=source&distro=esm-infra-legacy%2Ftrusty

Affected ranges

Type: ECOSYSTEM
Events: Introduced

0 Unknown introduced version / All previous versions are affected

Affected versions

1.*

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-2026-50251.json"

Ubuntu:Pro:16.04:LTS

unbound

Package

Name: unbound
Purl: pkg:deb/ubuntu/unbound?arch=source&distro=esm-infra-legacy%2Fxenial

Affected ranges

Type: ECOSYSTEM
Events: Introduced

0 Unknown introduced version / All previous versions are affected

Affected versions

1.*

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_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",
            "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-2026-50251.json"

Ubuntu:Pro:18.04:LTS

unbound

Package

Name: unbound
Purl: pkg:deb/ubuntu/unbound?arch=source&distro=esm-infra%2Fbionic

Affected ranges

Type: ECOSYSTEM
Events: Introduced

0 Unknown introduced version / All previous versions are affected

Affected versions

1.*

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_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",
            "binary_version": "1.6.7-1ubuntu2.6+esm4"
        }
    ]
}

Database specific

source

"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-50251.json"

Ubuntu:Pro:20.04:LTS

unbound

Package

Name: unbound
Purl: pkg:deb/ubuntu/unbound?arch=source&distro=esm-infra%2Ffocal

Affected ranges

Type: ECOSYSTEM
Events: Introduced

0 Unknown introduced version / All previous versions are affected

Affected versions

1.*

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_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",
            "binary_version": "1.9.4-2ubuntu1.11+esm1"
        }
    ]
}

Database specific

source

"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-50251.json"