Cache poisoning possible with label count discrepancy, RRSIG, and wildcards
Summary
| CVE | CVE-2026-11721 |
|---|---|
| State | PUBLISHED |
| Assigner | isc |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-07-22 15:16:51 UTC |
| Updated | 2026-07-22 20:33:11 UTC |
| 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. |
Risk And Classification
Primary CVSS: v3.1 7.5 HIGH from [email protected]
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Problem Types: CWE-1284 | CWE-1284 CWE-1284 Improper Validation of Specified Quantity in Input
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.1 | [email protected] | Secondary | 7.5 | HIGH | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N |
| 3.1 | CNA | DECLARED | 7.5 | HIGH | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N |
CVSS v3.1 Breakdown
Attack Vector
NetworkAttack Complexity
LowPrivileges Required
NoneUser Interaction
NoneScope
UnchangedConfidentiality
NoneIntegrity
HighAvailability
NoneCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | ISC | BIND 9 | affected 9.11.0 9.18.50 custom | Not specified |
| CNA | ISC | BIND 9 | affected 9.20.0 9.20.24 custom | Not specified |
| CNA | ISC | BIND 9 | affected 9.21.0 9.21.23 custom | Not specified |
| CNA | ISC | BIND 9 | affected 9.11.3-S1 9.18.50-S1 custom | Not specified |
| CNA | ISC | BIND 9 | affected 9.20.9-S1 9.20.24-S1 custom | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| kb.isc.org/docs/cve-2026-11721 | [email protected] | kb.isc.org | |
| downloads.isc.org/isc/bind9/9.21.24 | [email protected] | downloads.isc.org | |
| downloads.isc.org/isc/bind9/9.20.26 | [email protected] | downloads.isc.org | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
Vendor Comments And Credit
Discovery Credit
CNA: ISC would like to thank Qifan Zhang of Palo Alto Networks for bringing this vulnerability to our attention. (en)
Additional Advisory Data
Solutions
CNA: Upgrade to the patched release most closely related to your current version of BIND 9: 9.20.26, 9.21.24, or 9.20.26-S1.
Workarounds
CNA: No workarounds known.
Exploits
CNA: We are not aware of any active exploits.
There are currently no legacy QID mappings associated with this CVE.