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Fencer Vulns
medium 5.3

CVE-2026-5950 json

Unbounded resend loop in BIND 9 resolver

published 2026-05-20 5 mo ago modified 2026-07-23 3 mo ago also EUVD-2026-31109

cvss
5.3
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.7%
EPSS 0.7% chance of exploitation in 30 days, percentile 51%
public exploits
0
none known

Summary

An unbounded resend loop vulnerability exists in the BIND 9 resolver state machine during bad-server handling, enabling a remote unauthenticated attacker to cause severe resource exhaustion by sending queries that trigger specific retry conditions. This issue affects BIND 9 versions 9.18.36 through 9.18.48, 9.20.8 through 9.20.22, 9.21.7 through 9.21.21, 9.18.36-S1 through 9.18.48-S1, and 9.20.9-S1 through 9.20.22-S1.

Patch / fix

  • isc bind 9.18.49, 9.20.23, 9.21.21
  • bind9 Debian 12 1:9.18.49-1~deb12u2
  • bind9 Debian 13 1:9.20.23-1~deb13u1
  • bind9 Debian 14 1:9.20.23-1

debian advisories DEBIAN-CVE-2026-5950

  • bind9 Ubuntu 22.04 LTS 1:9.18.39-0ubuntu0.22.04.4
  • bind9 Ubuntu 24.04 LTS 1:9.18.39-0ubuntu0.24.04.5
  • bind9 Ubuntu 25.10 1:9.20.11-1ubuntu2.4
  • bind9 Ubuntu 26.04 LTS 1:9.20.18-1ubuntu2.1

ubuntu advisories UBUNTU-CVE-2026-5950

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • bind hummingbird 1 9.18.49-1.hum1
  • bind-libs hummingbird 1 9.18.49-1.hum1
  • bind-utils hummingbird 1 9.18.49-1.hum1
  • bind-chroot hummingbird 1 9.18.49-1.hum1
  • bind-dnssec-utils hummingbird 1 9.18.49-1.hum1

red hat advisories RHSA-2026:20334

  • bind SLE Module for Server Applications 15 SP7, SLE Module for Basesystem 15 SP7 9.20.23-150700.3.25.1
  • bind SLES for SAP applications 16.0, SLES 16.0 9.20.23-160000.1.1
  • bind SLES for SAP 15 SP6, SLES 15 SP6-LTSS 9.18.49-150600.3.26.1

suse advisories SUSE-SU-2026:2673-1SUSE-SU-2026:2676-1SUSE-SU-2026:22198-1

  • bind openSUSE Leap 16.0 9.20.23-160000.1.1
  • bind openSUSE Tumbleweed 9.20.23-1.1

opensuse advisories openSUSE-SU-2026:21123-1openSUSE-SU-2026:10874-1

  • bind Alpine 3.21, Alpine 3.20 9.18.49-r0
  • bind Alpine 3.24, Alpine 3.23, Alpine 3.22 9.20.23-r0

alpine advisories ALPINE-CVE-2026-5950

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • bind Azure Linux 3.0 9.20.23-1

azure linux advisories AZL-87102

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-5950 updated cvss 5.3

bind: Unbounded resend loop in BIND 9 resolver

  • Red Hat Enterprise Linux 6 bind, bind-sdb, bind-libs, bind-utils, bind-chroot Red Hat Enterprise Linux 7 bind, bind-sdb, bind-libs, bind-utils, bind-chroot, bind-pkcs11, +6 more Red Hat Enterprise Linux 8 bind, bind-sdb, bind9.16, bind-libs, bind-utils, bind-chroot, +14 more Red Hat Enterprise Linux 9 bind, dhcp, bind9.18, bind-libs, bind-utils, dhcp-relay, +11 more
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Enterprise Linux 10 bind
    affected: workaround, no fix available
  • Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-8, openshift/ose-rhel-coreos-9
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Hardened Images bind 9.18.49-1.hum1, bind-libs 9.18.49-1.hum1, bind-utils 9.18.49-1.hum1, bind-chroot 9.18.49-1.hum1, bind-dnssec-utils 9.18.49-1.hum1
    fixed: vendor fix RHSA-2026:20334

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
5 mo ago

Exploit prediction

0.66% chance of exploitation in the next 30 days, higher than 51% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Affected products

  • ISC BIND 9

Classification

Weakness
  • CWE-606 Unchecked Input for Loop Condition

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.