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CVE-2026-11721— Cache poisoning possible with label count discrepancy, RRSIG, and wildcards

Quick assessment

Affected
ISC BIND 9
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

ISC BIND 9是ISC组织的域名系统服务器。 ISC BIND 9 9.11.0版本至9.18.50版本、9.20.0版本至9.20.24版本、9.21.0版本至9.21.23版本、9.11.3-S1版本至9.18.50-S1版本和9.20.9-S1版本至9.20.24-S1版本存在输入验证错误漏洞，该漏洞源于RRSIG的标签数量小于所在区域的标签数量，导致named为区域产生比攻击者区域更短的通配符名称，可能导致缓存中毒。

CVSS 7.5 · High EPSS 0.40% · P31

Affected Version Matrix 5

VendorProduct Version RangeStatus
ISC BIND 9 9.11.0≤ 9.18.50 affected
9.20.0≤ 9.20.24 affected
9.21.0≤ 9.21.23 affected
9.11.3-S1≤ 9.18.50-S1 affected
9.20.9-S1≤ 9.20.24-S1 affected
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I. Basic Information for CVE-2026-11721

Vulnerability Information
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Vulnerability Title
Cache poisoning possible with label count discrepancy, RRSIG, and wildcards
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
CWE-1284
Source: CVE Program / CVE List V5
Vulnerability Title
ISC BIND 9 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
ISC BIND 9是ISC组织的域名系统服务器。 ISC BIND 9 9.11.0版本至9.18.50版本、9.20.0版本至9.20.24版本、9.21.0版本至9.21.23版本、9.11.3-S1版本至9.18.50-S1版本和9.20.9-S1版本至9.20.24-S1版本存在输入验证错误漏洞，该漏洞源于RRSIG的标签数量小于所在区域的标签数量，导致named为区域产生比攻击者区域更短的通配符名称，可能导致缓存中毒。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
ISC BIND 9 9.11.0 ~ 9.18.50 -

II. Public POCs for CVE-2026-11721

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III. Intelligence Information for CVE-2026-11721

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Vendor Advisories for CVE-2026-11721 (2)

Vendor Pages for CVE-2026-11721 (1)

Same Patch Batch · ISC · 2026-07-22 · 9 CVEs total

CVE-2026-13321 8.6 HIGH DNSSEC Validation Bypass via Out-of-Zone NSEC Next Field
CVE-2026-11605 7.5 HIGH Unnecessary validation of DNSSEC signed records
CVE-2026-11331 7.5 HIGH Potential wildcard CNAME RPZ policy bypass
CVE-2026-11622 7.5 HIGH Potential memory usage beyond configured limits
CVE-2026-12617 7.5 HIGH Record ordering based unexpected exit with CNAME or DNAME
CVE-2026-13204 7.5 HIGH Unexpected exit in certain situations with NSEC and NSEC3 both present
CVE-2026-10723 6.8 MEDIUM Incorrect acceptance of NSEC3 records
CVE-2026-10822 6.5 MEDIUM Key Record using PRIVATEDNS algorithm may lead to unexpected exit

IV. Related Vulnerabilities

Same product: BIND 9
Same vendor: ISC
Same weakness: CWE-1284

V. Comments for CVE-2026-11721

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