CVE-2026-77119: NSEC3 insecure-referral proof can use unrelated cached NSEC3 RRsets
A validly signed NSEC3 from an unrelated sibling zone may be accepted as an insecurity proof, downgrading a secure delegation and letting a forged unsigned answer through. This issue affects BIND 9 versions 9.11.0 through 9.18.50, 9.20.0 through 9.20.27, 9.21.0 through 9.21.25, 9.11.3-S1 through 9.18.50-S1, and 9.20.9-S1 through 9.20.27-S1.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
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ubuntu/bind9to a version that resolves this vulnerability.Fixed in 1:9.9.5.dfsg-3ubuntu0.19+esm15 - Upgrade
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ubuntu/bind9to a version that resolves this vulnerability.Fixed in 1:9.10.3.dfsg.P4-8ubuntu1.19+esm11 - Upgrade
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ubuntu/bind9to a version that resolves this vulnerability.Fixed in 1:9.11.3+dfsg-1ubuntu1.19+esm6 - Upgrade
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ubuntu/bind9to a version that resolves this vulnerability.Fixed in 1:9.18.30-0ubuntu0.20.04.2+esm3 - Upgrade
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ubuntu/bind9to a version that resolves this vulnerability.Fixed in 1:9.18.39-0ubuntu0.22.04.7 - Upgrade
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ubuntu/bind9to a version that resolves this vulnerability.Fixed in 1:9.18.39-0ubuntu0.24.04.8 - Upgrade
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ubuntu/bind9to a version that resolves this vulnerability.Fixed in 1:9.20.24-1ubuntu3.1 - Upgrade
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ubuntu/bind9to a version that resolves this vulnerability.Fixed in 1:9.20.24-1ubuntu0.4 - Upgrade
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ISC BIND 9to a version that resolves this vulnerability.Fixed in 9.20.29 - Upgrade
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ISC BIND 9to a version that resolves this vulnerability.Fixed in 9.21.26 - Upgrade
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ISC BIND 9to a version that resolves this vulnerability.Fixed in 9.20.29-S1
Event History
Frequently Asked Questions
Which deployments are affected?
The issue affects ISC BIND 9 releases 9.11.0 through 9.18.50, 9.20.0 through 9.20.27, 9.21.0 through 9.21.25, 9.11.3-S1 through 9.18.50-S1, and 9.20.9-S1 through 9.20.27-S1.
What must an attacker do to exploit this issue?
An attacker needs a validly signed NSEC3 record from an unrelated sibling zone that BIND accepts as an insecurity proof. This can downgrade a secure delegation and allow a forged unsigned DNS answer to pass through.
What is the security impact?
The vulnerability affects integrity: it can cause a secure delegation to be treated as insecure and permit acceptance of forged unsigned answers. The supplied vector indicates network reachability, no required privileges or user interaction, and high attack complexity.