CVE-2026-11721: CWE-1284 Improper Validation of Specified Quantity in Input in ISC BIND 9
A vulnerability in ISC BIND 9 allows an attacker controlling a DNS zone to respond with an RRSIG containing fewer labels than the zone, causing the DNS server to generate a wildcard name for a shorter zone. This can lead to cache poisoning if the resolver has 'synth-from-dnssec' enabled, which is the default setting. The issue affects multiple BIND 9 versions from 9.11.0 through 9.21.23 and their respective S1 variants.
AI Analysis
Technical Summary
CVE-2026-11721 is a vulnerability in ISC BIND 9 where an attacker’s DNS zone can respond with an RRSIG having fewer labels than the zone itself. This discrepancy causes the 'named' DNS server to produce a wildcard name for a zone shorter than the attacker's zone, potentially enabling cache poisoning attacks. The vulnerability requires the resolver to have 'synth-from-dnssec' set to yes, which is the default configuration. Affected versions include BIND 9.11.0 through 9.18.50, 9.20.0 through 9.20.24, 9.21.0 through 9.21.23, and their S1 variants. The CVSS v3.1 base score is 7.5, indicating a high severity with network attack vector, low attack complexity, no privileges or user interaction required, unchanged scope, no confidentiality impact, high integrity impact, and no availability impact. No official patch or remediation level has been published as of the data provided.
Potential Impact
Successful exploitation can result in DNS cache poisoning, allowing an attacker to inject malicious DNS records into the resolver's cache. This compromises the integrity of DNS responses, potentially redirecting users to malicious sites or disrupting DNS resolution. There is no direct confidentiality or availability impact reported.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, administrators should review their DNS resolver configurations, particularly the 'synth-from-dnssec' setting. If feasible, temporarily disabling 'synth-from-dnssec' may mitigate the risk, but this should be balanced against operational requirements. Monitor ISC advisories for updates and apply patches promptly once released.
CVE-2026-11721: CWE-1284 Improper Validation of Specified Quantity in Input in ISC BIND 9
Description
A vulnerability in ISC BIND 9 allows an attacker controlling a DNS zone to respond with an RRSIG containing fewer labels than the zone, causing the DNS server to generate a wildcard name for a shorter zone. This can lead to cache poisoning if the resolver has 'synth-from-dnssec' enabled, which is the default setting. The issue affects multiple BIND 9 versions from 9.11.0 through 9.21.23 and their respective S1 variants.
CVSS v3.1
Score 7.5high
Affected software
pkg:github/isc/bind9Run on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-11721 is a vulnerability in ISC BIND 9 where an attacker’s DNS zone can respond with an RRSIG having fewer labels than the zone itself. This discrepancy causes the 'named' DNS server to produce a wildcard name for a zone shorter than the attacker's zone, potentially enabling cache poisoning attacks. The vulnerability requires the resolver to have 'synth-from-dnssec' set to yes, which is the default configuration. Affected versions include BIND 9.11.0 through 9.18.50, 9.20.0 through 9.20.24, 9.21.0 through 9.21.23, and their S1 variants. The CVSS v3.1 base score is 7.5, indicating a high severity with network attack vector, low attack complexity, no privileges or user interaction required, unchanged scope, no confidentiality impact, high integrity impact, and no availability impact. No official patch or remediation level has been published as of the data provided.
Potential Impact
Successful exploitation can result in DNS cache poisoning, allowing an attacker to inject malicious DNS records into the resolver's cache. This compromises the integrity of DNS responses, potentially redirecting users to malicious sites or disrupting DNS resolution. There is no direct confidentiality or availability impact reported.
Mitigation Recommendations
Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, administrators should review their DNS resolver configurations, particularly the 'synth-from-dnssec' setting. If feasible, temporarily disabling 'synth-from-dnssec' may mitigate the risk, but this should be balanced against operational requirements. Monitor ISC advisories for updates and apply patches promptly once released.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- isc
- Date Reserved
- 2026-06-09T01:19:47.697Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a60d93c9c2644c7f8363a03
Added to database: 07/22/2026, 14:52:44 UTC
Last enriched: 07/22/2026, 15:07:49 UTC
Last updated: 07/22/2026, 16:00:58 UTC
Views: 3
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