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OpenAdvisories
Medium · 5.3 Public exploit CVE-2026-5950 EUVD-2026-31109GHSA-2pjm-rchf-gxmp

Unbounded resend loop in BIND 9 resolver

Published May 20, 2026 · Updated May 20, 2026 · Assigned by isc

Vendor: ISC Product: BIND 9 Package: bind Package: bind Package: bind9 Package: bind9 Package: bind9-libs Package: isc-dhcp Ecosystem: Alpine Ecosystem: Azure Linux Ecosystem: Debian Ecosystem: Ubuntu

Description

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.

Affected products

VendorProductAffectedFixed
ISC BIND 9 9.18.36 – ≤ 9.18.48, 9.20.8 – ≤ 9.20.22, 9.21.7 – ≤ 9.21.21, 9.18.36-S1 – ≤ 9.18.48-S1, 9.20.9-S1 – ≤ 9.20.22-S1 —

Fixed in Linux distributions

Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.

Debian

Security tracker ↗
ReleasePackageFixed inAdvisory
Debian 14 bind9 1:9.20.23-1 —
Debian 13 bind9 1:9.20.23-1~deb13u1 —
Debian 12 bind9 1:9.18.49-1~deb12u2 —

Ubuntu

Security tracker ↗
ReleasePackageFixed inAdvisory
Ubuntu 26.04 LTS bind9 1:9.20.18-1ubuntu2.1 —
Ubuntu 26.04 LTS isc-dhcp No fix yet —
Ubuntu 25.10 bind9 1:9.20.11-1ubuntu2.4 —
Ubuntu 25.10 isc-dhcp No fix yet —
Ubuntu 24.04 LTS bind9 1:9.18.39-0ubuntu0.24.04.5 —
Ubuntu 24.04 LTS isc-dhcp No fix yet —
Ubuntu 22.04 LTS bind9 1:9.18.39-0ubuntu0.22.04.4 —
Ubuntu 22.04 LTS bind9-libs No fix yet —
Ubuntu 20.04 LTS bind9-libs No fix yet —
Show 1 more (older releases, extended support, other products)
ReleasePackageFixed inAdvisory
Ubuntu 18.04 LTS isc-dhcp No fix yet —

Red Hat

Security tracker ↗
ReleasePackageFixed inAdvisory
Red Hat Hardened Images 1 bind +6 9.18.49-1.hum1 RHSA-2026:20334

SUSE

Security tracker ↗
ReleasePackageFixed inAdvisory
SLES 15 SP7 bind 9.20.23-150700.3.25.1 SUSE-SU-2026:2673-1
SLES 15 SP6 bind 9.18.49-150600.3.26.1 SUSE-SU-2026:2676-1
Show 3 more (older releases, extended support, other products)
ReleasePackageFixed inAdvisory
SLES for SAP 16.0 bind 9.20.23-160000.1.1 SUSE-SU-2026:22198-1
SLES for SAP 15 SP6 bind 9.18.49-150600.3.26.1 SUSE-SU-2026:2676-1
SLES 16.0 bind 9.20.23-160000.1.1 SUSE-SU-2026:22198-1

openSUSE

Security tracker ↗
ReleasePackageFixed inAdvisory
openSUSE Tumbleweed bind 9.20.23-1.1 openSUSE-SU-2026:10874-1
openSUSE Leap 16.0 bind 9.20.23-160000.1.1 openSUSE-SU-2026:21123-1

Alpine

Security tracker ↗
ReleasePackageFixed inAdvisory
Alpine v3.24 bind 9.20.23-r0 —
Alpine v3.23 bind 9.20.23-r0 —
Alpine v3.22 bind 9.20.23-r0 —
Alpine v3.21 bind 9.18.49-r0 —
Alpine v3.20 bind 9.18.49-r0 —

Amazon Linux

ReleasePackageFixed inAdvisory
Amazon Linux 2023 bind +7 32:9.18.49-1.amzn2023.0.1 ALAS2023-2026-1755
Amazon Linux 2 bind +15 32:9.11.4-26.P2.amzn2.13.16 ALAS2-2026-3353

Azure Linux

ReleasePackageFixed inAdvisory
Azure Linux 3 bind 9.20.23-1 —

Public exploits

Exploit or proof-of-concept code for this vulnerability is publicly available, which lowers the bar for attackers. Treat it as a reason to patch sooner.

Third-party code, not reviewed by us. Public PoCs are sometimes fake or contain malware. Read the code first and run it only in an isolated lab, against systems you are authorised to test.

GitHub 1 repository

Sources: PoC-in-GitHub, Metasploit Framework, Exploit-DB — updated daily. Only links are listed; no exploit code is hosted here.

Advisories 9

References