CVE-2026-11721
Cache poisoning possible with label count discrepancy, RRSIG, and wildcards
Description
It is possible for an attacker's zone to respond to a query with an RRSIG that has a smaller number of labels than the zone in which the RRSIG is contained. This causes `named` to produce a wildcard name for a zone that is shorter than the attacker's zone, which can result in cache poisoning. For this attack to have any effect, the resolver under attack must have set `synth-from-dnssec yes;` (which is the default). This issue affects BIND 9 versions 9.11.0 through 9.18.50, 9.20.0 through 9.20.24, 9.21.0 through 9.21.23, 9.11.3-S1 through 9.18.50-S1, and 9.20.9-S1 through 9.20.24-S1.
INFO
Published Date :
July 22, 2026, 3:16 p.m.
Last Modified :
July 22, 2026, 3:16 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | HIGH | [email protected] |
Solution
- Update BIND 9 to a patched version.
- Verify resolver configuration regarding `synth-from-dnssec`.
- Monitor for cache poisoning attempts.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-11721.
| URL | Resource |
|---|---|
| https://downloads.isc.org/isc/bind9/9.20.26 | |
| https://downloads.isc.org/isc/bind9/9.21.24 | |
| https://kb.isc.org/docs/cve-2026-11721 |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-11721 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-11721
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-11721 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-11721 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
New CVE Received by [email protected]
Jul. 22, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'ISC', 'product': 'BIND 9', 'versions': [{'status': 'affected', 'version': '9.11.0', 'versionType': 'custom', 'lessThanOrEqual': '9.18.50'}, {'status': 'affected', 'version': '9.20.0', 'versionType': 'custom', 'lessThanOrEqual': '9.20.24'}, {'status': 'affected', 'version': '9.21.0', 'versionType': 'custom', 'lessThanOrEqual': '9.21.23'}, {'status': 'affected', 'version': '9.11.3-S1', 'versionType': 'custom', 'lessThanOrEqual': '9.18.50-S1'}, {'status': 'affected', 'version': '9.20.9-S1', 'versionType': 'custom', 'lessThanOrEqual': '9.20.24-S1'}], 'defaultStatus': 'unaffected'}] Added Description It is possible for an attacker's zone to respond to a query with an RRSIG that has a smaller number of labels than the zone in which the RRSIG is contained. This causes `named` to produce a wildcard name for a zone that is shorter than the attacker's zone, which can result in cache poisoning. For this attack to have any effect, the resolver under attack must have set `synth-from-dnssec yes;` (which is the default). This issue affects BIND 9 versions 9.11.0 through 9.18.50, 9.20.0 through 9.20.24, 9.21.0 through 9.21.23, 9.11.3-S1 through 9.18.50-S1, and 9.20.9-S1 through 9.20.24-S1. Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N Added CWE CWE-1284 Added Reference https://downloads.isc.org/isc/bind9/9.20.26 Added Reference https://downloads.isc.org/isc/bind9/9.21.24 Added Reference https://kb.isc.org/docs/cve-2026-11721