unbound — security advisory
Novel vulnerabilities to launch algorithmic complexity attacks on DNSSEC have been researched under the term 'ReTrap'. These result in degradation of service when malicious zones are used to serve the algorithmic complexity vulnerabilities. NLnet Labs Unbound up to and including 1.26.0 is vulnerable to some of them. TagTrap, where the triple(Zone, Algo, KeyTag) matching mechanism introduces a significant attack vector when resolvers handle malicious responses containing numerous mismatched DNSKEY, RRSIG, and DS record. DelegationTrap, where constructing the chain-of-trust requires iterative validation of DNSKEY and DS records from the root zone downward. For deeply nested domains, this results in significant computational overhead. NsecTrap, where responses with excessive invalid NSEC records compel the resolver to validate each one. AdditionalTrap, where Unbound by default would try to DNSSEC validate the ADDITIONAL section as well. This can be exploited to waste validation resources by malicious users.
- Products
- unbound
- Affected versions
- 1.13.1-1ubuntu1, 1.13.1-1ubuntu3, 1.13.1-1ubuntu5, 1.13.1-1ubuntu5.1, 1.13.1-1ubuntu5.10, 1.13.1-1ubuntu5.11, 1.13.1-1ubuntu5.12, 1.13.1-1ubuntu5.13, 1.13.1-1ubuntu5.14, 1.13.1-1ubuntu5.15, 1.13.1-1ubuntu5.16, 1.13.1-1ubuntu5.2, 1.13.1-1ubuntu5.3, 1.13.1-1ubuntu5.4, 1.13.1-1ubuntu5.5, 1.13.1-1ubuntu5.7, 1.13.1-1ubuntu5.8, 1.17.1-2, 1.18.0-2ubuntu1, 1.18.0-2ubuntu2, 1.19.1-1ubuntu1, 1.19.2-1ubuntu1, 1.19.2-1ubuntu3, 1.19.2-1ubuntu3.1, 1.19.2-1ubuntu3.10, 1.19.2-1ubuntu3.2, 1.19.2-1ubuntu3.3, 1.19.2-1ubuntu3.4, 1.19.2-1ubuntu3.5, 1.19.2-1ubuntu3.6, 1.19.2-1ubuntu3.7, 1.19.2-1ubuntu3.8, 1.19.2-1ubuntu3.9, 1.22.0-2ubuntu2, 1.22.0-2ubuntu4, 1.24.2-1ubuntu1, 1.24.2-1ubuntu2, 1.24.2-1ubuntu2.1, 1.24.2-1ubuntu2.2, 1.24.2-1ubuntu2.3, 1.25.1-1ubuntu1, 1.25.1-1ubuntu3, 1.4.20-1, 1.4.21-1, 1.4.21-1ubuntu1, 1.4.21-1ubuntu2, 1.4.22-1ubuntu1, 1.4.22-1ubuntu2, 1.4.22-1ubuntu3, 1.4.22-1ubuntu4, 1.4.22-1ubuntu4.14.04.1, 1.4.22-1ubuntu4.14.04.2, 1.4.22-1ubuntu4.14.04.3, 1.4.22-1ubuntu4.14.04.3+esm1, 1.4.22-1ubuntu4.14.04.3+esm2, 1.4.22-1ubuntu4.14.04.3+esm3, 1.4.22-1ubuntu4.14.04.3+esm4, 1.4.22-1ubuntu6, 1.5.7-1ubuntu1, 1.5.7-1ubuntu2, 1.5.8-1ubuntu1, 1.5.8-1ubuntu1.1, 1.5.8-1ubuntu1.1+esm1, 1.5.8-1ubuntu1.1+esm2, 1.5.8-1ubuntu1.1+esm3, 1.5.8-1ubuntu1.1+esm4, 1.6.5-1, 1.6.7-1, 1.6.7-1build1, 1.6.7-1ubuntu1, 1.6.7-1ubuntu2, 1.6.7-1ubuntu2.1, 1.6.7-1ubuntu2.2, 1.6.7-1ubuntu2.3, 1.6.7-1ubuntu2.4, 1.6.7-1ubuntu2.5, 1.6.7-1ubuntu2.6, 1.6.7-1ubuntu2.6+esm2, 1.6.7-1ubuntu2.6+esm3, 1.6.7-1ubuntu2.6+esm4, 1.6.7-1ubuntu2.6+esm5, 1.9.0-2ubuntu1, 1.9.0-2ubuntu2, 1.9.4-2, 1.9.4-2ubuntu1, 1.9.4-2ubuntu1.1, 1.9.4-2ubuntu1.11, 1.9.4-2ubuntu1.11+esm1, 1.9.4-2ubuntu1.11+esm2, 1.9.4-2ubuntu1.2, 1.9.4-2ubuntu1.3, 1.9.4-2ubuntu1.4, 1.9.4-2ubuntu1.5, 1.9.4-2ubuntu1.6, 1.9.4-2ubuntu1.8, 1.9.4-2ubuntu1.9
- Fixed versions
- 1.13.1-1ubuntu5.17, 1.19.2-1ubuntu3.12, 1.24.2-1ubuntu2.4, 1.4.22-1ubuntu4.14.04.3+esm5, 1.5.8-1ubuntu1.1+esm5, 1.6.7-1ubuntu2.6+esm6, 1.9.4-2ubuntu1.11+esm3
- CVEs
- CVE-2026-85501
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 31 Oct 2026, 16:39 UTC · Revision 1
Source evidence
Novel vulnerabilities to launch algorithmic complexity attacks on DNSSEC have been researched under the term 'ReTrap'. These result in degradation of service when malicious zones are used to serve the algorithmic complexity vulnerabilities. NLnet Labs Unbound up to and including 1.26.0 is vulnerable to some of them. TagTrap, where the triple(Zone, Algo, KeyTag) matching mechanism introduces a significant attack vector when resolvers handle malicious responses containing numerous mismatched DNSKEY, RRSIG, and DS record. DelegationTrap, where constructing the chain-of-trust requires iterative validation of DNSKEY and DS records from the root zone downward. For deeply nested domains, this results in significant computational overhead. NsecTrap, where responses with excessive invalid NSEC records compel the resolver to validate each one. AdditionalTrap, where Unbound by default would try to DNSSEC validate the ADDITIONAL section as well. This can be exploited to waste validation resources by malicious users.
osv:UBUNTU-CVE-2026-85501
unbound
Fixed versions: 1.4.22-1ubuntu4.14.04.3+esm5
unbound
Fixed versions: 1.5.8-1ubuntu1.1+esm5
unbound
Fixed versions: 1.6.7-1ubuntu2.6+esm6
unbound
Fixed versions: 1.9.4-2ubuntu1.11+esm3
unbound
Fixed versions: 1.13.1-1ubuntu5.17
unbound
Fixed versions: 1.19.2-1ubuntu3.12
unbound
Fixed versions: Not specified
unbound
Fixed versions: 1.24.2-1ubuntu2.4
Complete source record
{
"id": "b5561e3dcdc7d1a691eda7b6c2a583c92a00aea18c88a33769e45eb2e7da9a1c",
"url": "https://osv.dev/vulnerability/UBUNTU-CVE-2026-85501",
"method": "structured",
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"kind": "advisory",
"title": "UBUNTU-CVE-2026-85501",
"summary": "Novel vulnerabilities to launch algorithmic complexity attacks on DNSSEC have been researched under the term 'ReTrap'. These result in degradation of service when malicious zones are used to serve the algorithmic complexity vulnerabilities. NLnet Labs Unbound up to and including 1.26.0 is vulnerable to some of them. TagTrap, where the triple(Zone, Algo, KeyTag) matching mechanism introduces a significant attack vector when resolvers handle malicious responses containing numerous mismatched DNSKEY, RRSIG, and DS record. DelegationTrap, where constructing the chain-of-trust requires iterative validation of DNSKEY and DS records from the root zone downward. For deeply nested domains, this results in significant computational overhead. NsecTrap, where responses with excessive invalid NSEC records compel the resolver to validate each one. AdditionalTrap, where Unbound by default would try to DNSSEC validate the ADDITIONAL section as well. This can be exploited to waste validation resources by malicious users.",
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{
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{
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{
"value": "1.13.1-1ubuntu5.7",
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{
"value": "1.13.1-1ubuntu5.8",
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],
"severity": "high",
"structured": {
"id": "UBUNTU-CVE-2026-85501",
"aliases": [
"UBUNTU-CVE-2026-85501"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"
},
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
},
{
"type": "Ubuntu",
"score": "medium"
}
],
"affected": [
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
},
{
"fixed": "1.4.22-1ubuntu4.14.04.3+esm5"
}
]
}
],
"package": {
"name": "unbound",
"purl": "pkg:deb/ubuntu/unbound?arch=source&distro=esm-infra-legacy%2Ftrusty",
"ecosystem": "Ubuntu:Pro:14.04:LTS"
},
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"1.4.21-1",
"1.4.21-1ubuntu1",
"1.4.21-1ubuntu2",
"1.4.22-1ubuntu1",
"1.4.22-1ubuntu2",
"1.4.22-1ubuntu3",
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"1.4.22-1ubuntu4.14.04.1",
"1.4.22-1ubuntu4.14.04.2",
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"1.4.22-1ubuntu4.14.04.3+esm2",
"1.4.22-1ubuntu4.14.04.3+esm3",
"1.4.22-1ubuntu4.14.04.3+esm4"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-85501.json"
},
"ecosystem_specific": {
"binaries": [
{
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"binary_version": "1.4.22-1ubuntu4.14.04.3+esm5"
},
{
"binary_name": "python-unbound",
"binary_version": "1.4.22-1ubuntu4.14.04.3+esm5"
},
{
"binary_name": "unbound",
"binary_version": "1.4.22-1ubuntu4.14.04.3+esm5"
},
{
"binary_name": "unbound-anchor",
"binary_version": "1.4.22-1ubuntu4.14.04.3+esm5"
},
{
"binary_name": "unbound-host",
"binary_version": "1.4.22-1ubuntu4.14.04.3+esm5"
}
],
"availability": "Available with Ubuntu Pro with Legacy support add-on: https://ubuntu.com/pro"
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
},
{
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}
]
}
],
"package": {
"name": "unbound",
"purl": "pkg:deb/ubuntu/unbound?arch=source&distro=esm-infra-legacy%2Fxenial",
"ecosystem": "Ubuntu:Pro:16.04:LTS"
},
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"1.5.7-1ubuntu1",
"1.5.7-1ubuntu2",
"1.5.8-1ubuntu1",
"1.5.8-1ubuntu1.1",
"1.5.8-1ubuntu1.1+esm1",
"1.5.8-1ubuntu1.1+esm2",
"1.5.8-1ubuntu1.1+esm3",
"1.5.8-1ubuntu1.1+esm4"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-85501.json"
},
"ecosystem_specific": {
"binaries": [
{
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},
{
"binary_name": "python-unbound",
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},
{
"binary_name": "unbound",
"binary_version": "1.5.8-1ubuntu1.1+esm5"
},
{
"binary_name": "unbound-anchor",
"binary_version": "1.5.8-1ubuntu1.1+esm5"
},
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],
"modified": "2026-10-21T23:02:26.287970492Z",
"provider": "osv",
"upstream": [
"CVE-2026-85501"
],
"references": [
"https://ubuntu.com/security/CVE-2026-85501",
"https://www.cve.org/CVERecord?id=CVE-2026-85501",
"https://nlnetlabs.nl/downloads/unbound/CVE-2026-85501.txt",
"https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-85501.txt",
"https://ubuntu.com/security/notices/USN-8946-1"
]
},
"related_cves": [
{
"value": "CVE-2026-85501",
"evidence": "/upstream"
}
],
"security_relevant": true,
"severity_evidence": "/severity/1/score"
},
"source_id": "core-osv",
"document_id": 401070,
"published_at": "2026-09-16T09:17:00+00:00"
}