DNS cache poisoning via invalid RRSIG label count
Published Jul 22, 2026 · Updated Jul 22, 2026
Cache poisoning in Internet Systems Consortium BIND 9 allows remote attackers to corrupt resolver cache entries via signed wildcard responses. named accepts an RRSIG whose Labels field is smaller than the label count in its Signer Name, then synthesizes a wildcard name above the attacker's zone. A resolver is exposed when synth-from-dnssec is enabled, as it is by default, allowing forged DNS data to influence subsequent answers.
Summary
What happened
Cache poisoning in Internet Systems Consortium BIND 9 allows remote attackers to corrupt resolver cache entries via signed wildcard responses. named accepts an RRSIG whose Labels field is smaller than the label count in its Signer Name, then synthesizes a wildcard name above the attacker's zone. A resolver is exposed when synth-from-dnssec is enabled, as it is by default, allowing forged DNS data to influence subsequent answers.
The record
- CVE
- CVE-2026-11721
- Published
- Jul 22, 2026
- Updated
- Jul 22, 2026
- Vendor
- Internet Systems Consortium
- Product
- BIND 9
- Classifications
- CWE-1284, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jul 22, 2026CVE publishedPublication date reported by the CVE source.
- Jul 22, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=9.11.0 <=9.18.50
- Affected versionversion=9.11.3-S1 <=9.18.50-S1
- Affected versionversion=9.20.0 <=9.20.24
- Affected versionversion=9.20.9-S1 <=9.20.24-S1
- Affected versionversion=9.21.0 <=9.21.23
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What is affected?
Published CVSS scores
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Attacks
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Weakness, pattern, technique
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Technologies
Your stack
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Your stack
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