Unbounded resend loop in BIND 9 resolver
Published May 20, 2026
5.3
MEDIUMCVSS 3.1
EPSS 0.80%
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
-
- Version 9.18.36StatusaffectedConstraints<=9.18.48
- Version 9.18.36-S1StatusaffectedConstraints<=9.18.48-S1
- Version 9.20.8StatusaffectedConstraints<=9.20.22
- Version 9.20.9-S1StatusaffectedConstraints<=9.20.22-S1
- Version 9.21.7StatusaffectedConstraints<=9.21.21
- Version
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
No data.
Red Hat Hardened Images
bind-main-9.18.49-1.hum1
Fixed · RHSA-2026:20334
Red Hat Enterprise Linux 10
bind
Affected
Red Hat Enterprise Linux 6
bind
Fix deferred
Red Hat Enterprise Linux 7
bind
Fix deferred
Red Hat Enterprise Linux 8
bind
Fix deferred
Red Hat Enterprise Linux 8
bind9.16
Fix deferred
Red Hat Enterprise Linux 9
bind
Fix deferred
Red Hat Enterprise Linux 9
bind9.18
Fix deferred
Red Hat Enterprise Linux 9
dhcp
Fix deferred
Red Hat OpenShift Container Platform 4
openshift/ose-rhel-coreos-8
Fix deferred
Red Hat OpenShift Container Platform 4
openshift/ose-rhel-coreos-9
Fix deferred
| Product | Package | State | Advisory |
|---|---|---|---|
| Red Hat Hardened Images | bind-main-9.18.49-1.hum1 | Fixed | RHSA-2026:20334 |
| Red Hat Enterprise Linux 10 | bind | Affected | n/a |
| Red Hat Enterprise Linux 6 | bind | Fix deferred | n/a |
| Red Hat Enterprise Linux 7 | bind | Fix deferred | n/a |
| Red Hat Enterprise Linux 8 | bind | Fix deferred | n/a |
| Red Hat Enterprise Linux 8 | bind9.16 | Fix deferred | n/a |
| Red Hat Enterprise Linux 9 | bind | Fix deferred | n/a |
| Red Hat Enterprise Linux 9 | bind9.18 | Fix deferred | n/a |
| Red Hat Enterprise Linux 9 | dhcp | Fix deferred | n/a |
| Red Hat OpenShift Container Platform 4 | openshift/ose-rhel-coreos-8 | Fix deferred | n/a |
| Red Hat OpenShift Container Platform 4 | openshift/ose-rhel-coreos-9 | Fix deferred | n/a |
No package ranges for this CVE.
Remediation
Vendor solution
Upgrade to the patched release most closely related to your current version of BIND 9: 9.18.49, 9.20.23, 9.21.22, 9.18.49-S1, or 9.20.23-S1.
Red Hat statement
Moderate: This flaw in the BIND 9 resolver's state machine can lead to severe resource exhaustion. A remote, unauthenticated attacker could exploit this by sending specially crafted queries that trigger an unbounded resend loop during bad-server handling, potentially causing a denial of service in affected Red Hat products utilizing BIND as a resolver.
Red Hat mitigation
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.
Metrics
No CVSS v4.0 score for this CVE.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
No CVSS v3.0 score for this CVE.
No CVSS v2.0 score for this CVE.
This CVE is not in the KEV list.
CISA SSVC (Vulnrichment)
Stakeholder-Specific Vulnerability Categorization from CISA ADP.
Exploitation
NoneAutomatable
YesTechnical Impact
PartialDecision
n/aAssessed May 20, 2026 · SSVC 2.0.3
Estimated probability of exploitation in the wild in the next 30 days (FIRST EPSS). As of Oct 1, 2026.
Score over time
May–Oct 2026- EPSS v4
- EPSS v5
Percentile over time
- EPSS v4
- EPSS v5
Table of values (3 key points)
Flat stretches are collapsed; showing up to 120 newest points.
| Date | Score | Percentile | Model |
|---|---|---|---|
| Oct 1, 2026 | 0.80% (0.00798) | 54.90th | v5 (v2026.06.15) |
| Jun 15, 2026 | 0.50% (0.00504) | 38.84th | v5 (v2026.06.15) |
| May 21, 2026 | 0.04% (0.00043) | 13.08th | v4 (v2025.03.14) |
References (8)
- https://access.redhat.com/security/cve/CVE-2026-5950 Vendor Advisory
- https://bugzilla.redhat.com/show_bug.cgi?id=2479773 Issue Tracking
- https://downloads.isc.org/isc/bind9/9.18.49 patch
- https://downloads.isc.org/isc/bind9/9.20.23 patch
- https://downloads.isc.org/isc/bind9/9.21.22 patch
- https://kb.isc.org/docs/cve-2026-5950 vendor-advisoryVendor Advisory
- https://nvd.nist.gov/vuln/detail/CVE-2026-5950
- https://www.cve.org/CVERecord?id=CVE-2026-5950
| Link | Providers | Tags |
|---|---|---|
| https://access.redhat.com/security/cve/CVE-2026-5950 | Vendor Advisory | |
| https://bugzilla.redhat.com/show_bug.cgi?id=2479773 | Issue Tracking | |
| https://downloads.isc.org/isc/bind9/9.18.49 | patch | |
| https://downloads.isc.org/isc/bind9/9.20.23 | patch | |
| https://downloads.isc.org/isc/bind9/9.21.22 | patch | |
| https://kb.isc.org/docs/cve-2026-5950 | vendor-advisoryVendor Advisory | |
| https://nvd.nist.gov/vuln/detail/CVE-2026-5950 | ||
| https://www.cve.org/CVERecord?id=CVE-2026-5950 |
Change history (0)
No recorded changes yet.