CVE-2026-11721 (GCVE-0-2026-11721)

Vulnerability from cvelistv5 – Published: 2026-07-22 14:13 – Updated: 2026-07-22 14:13
VLAI
Title
Cache poisoning possible with label count discrepancy, RRSIG, and wildcards
Summary
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.
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
CWE
  • CWE-1284 - Improper Validation of Specified Quantity in Input
Assigner
isc
References
Impacted products
Vendor Product Version
ISC BIND 9 Affected: 9.11.0 , ≤ 9.18.50 (custom)
Affected: 9.20.0 , ≤ 9.20.24 (custom)
Affected: 9.21.0 , ≤ 9.21.23 (custom)
Affected: 9.11.3-S1 , ≤ 9.18.50-S1 (custom)
Affected: 9.20.9-S1 , ≤ 9.20.24-S1 (custom)
Create a notification for this product.
Date Public
2026-07-22 00:00
Credits
ISC would like to thank Qifan Zhang of Palo Alto Networks for bringing this vulnerability to our attention.
Show details on NVD website
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{
  "containers": {
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      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "BIND 9",
          "vendor": "ISC",
          "versions": [
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              "status": "affected",
              "version": "9.20.0",
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              "version": "9.21.0",
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              "lessThanOrEqual": "9.18.50-S1",
              "status": "affected",
              "version": "9.11.3-S1",
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            {
              "lessThanOrEqual": "9.20.24-S1",
              "status": "affected",
              "version": "9.20.9-S1",
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      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
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                  "criteria": "cpe:2.3:a:isc:bind:*:*:*:*:*:*:*:*",
                  "versionEndIncluding": "9.18.50",
                  "versionStartIncluding": "9.11.0",
                  "vulnerable": true
                },
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                },
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      "credits": [
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          "value": "ISC would like to thank Qifan Zhang of Palo Alto Networks for bringing this vulnerability to our attention."
        }
      ],
      "datePublic": "2026-07-22T00:00:00.000Z",
      "descriptions": [
        {
          "lang": "en",
          "value": "It is possible for an attacker\u0027s 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\u0027s 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).\nThis 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."
        }
      ],
      "exploits": [
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          "value": "We are not aware of any active exploits."
        }
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      "impacts": [
        {
          "descriptions": [
            {
              "lang": "en",
              "value": "Potential cache poisoning."
            }
          ]
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "NONE",
            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "NONE",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-1284",
              "description": "CWE-1284 Improper Validation of Specified Quantity in Input",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-07-22T14:13:08.748Z",
        "orgId": "404fd4d2-a609-4245-b543-2c944a302a22",
        "shortName": "isc"
      },
      "references": [
        {
          "name": "CVE-2026-11721",
          "tags": [
            "vendor-advisory"
          ],
          "url": "https://kb.isc.org/docs/cve-2026-11721"
        },
        {
          "tags": [
            "patch"
          ],
          "url": "https://downloads.isc.org/isc/bind9/9.20.26"
        },
        {
          "tags": [
            "patch"
          ],
          "url": "https://downloads.isc.org/isc/bind9/9.21.24"
        }
      ],
      "solutions": [
        {
          "lang": "en",
          "value": "Upgrade to the patched release most closely related to your current version of BIND 9: 9.20.26, 9.21.24, or 9.20.26-S1."
        }
      ],
      "source": {
        "discovery": "EXTERNAL"
      },
      "title": "Cache poisoning possible with label count discrepancy, RRSIG, and wildcards",
      "workarounds": [
        {
          "lang": "en",
          "value": "No workarounds known."
        }
      ],
      "x_generator": {
        "engine": "cvelib 1.8.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "404fd4d2-a609-4245-b543-2c944a302a22",
    "assignerShortName": "isc",
    "cveId": "CVE-2026-11721",
    "datePublished": "2026-07-22T14:13:08.748Z",
    "dateReserved": "2026-06-09T01:19:47.697Z",
    "dateUpdated": "2026-07-22T14:13:08.748Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "nvd": "{\"cve\":{\"id\":\"CVE-2026-11721\",\"sourceIdentifier\":\"security-officer@isc.org\",\"published\":\"2026-07-22T15:16:51.837\",\"lastModified\":\"2026-07-22T15:16:51.837\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"It is possible for an attacker\u0027s 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\u0027s 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).\\nThis 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.\"}],\"affected\":[{\"source\":\"security-officer@isc.org\",\"affectedData\":[{\"vendor\":\"ISC\",\"product\":\"BIND 9\",\"defaultStatus\":\"unaffected\",\"versions\":[{\"version\":\"9.11.0\",\"lessThanOrEqual\":\"9.18.50\",\"versionType\":\"custom\",\"status\":\"affected\"},{\"version\":\"9.20.0\",\"lessThanOrEqual\":\"9.20.24\",\"versionType\":\"custom\",\"status\":\"affected\"},{\"version\":\"9.21.0\",\"lessThanOrEqual\":\"9.21.23\",\"versionType\":\"custom\",\"status\":\"affected\"},{\"version\":\"9.11.3-S1\",\"lessThanOrEqual\":\"9.18.50-S1\",\"versionType\":\"custom\",\"status\":\"affected\"},{\"version\":\"9.20.9-S1\",\"lessThanOrEqual\":\"9.20.24-S1\",\"versionType\":\"custom\",\"status\":\"affected\"}]}]}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"security-officer@isc.org\",\"type\":\"Primary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N\",\"baseScore\":7.5,\"baseSeverity\":\"HIGH\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"NONE\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"NONE\",\"integrityImpact\":\"HIGH\",\"availabilityImpact\":\"NONE\"},\"exploitabilityScore\":3.9,\"impactScore\":3.6}]},\"weaknesses\":[{\"source\":\"security-officer@isc.org\",\"type\":\"Secondary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-1284\"}]}],\"references\":[{\"url\":\"https://downloads.isc.org/isc/bind9/9.20.26\",\"source\":\"security-officer@isc.org\"},{\"url\":\"https://downloads.isc.org/isc/bind9/9.21.24\",\"source\":\"security-officer@isc.org\"},{\"url\":\"https://kb.isc.org/docs/cve-2026-11721\",\"source\":\"security-officer@isc.org\"}]}}",
    "redhat_vex": {
      "aggregate_severity": "Important",
      "current_release_date": "2026-07-22T15:42:10+00:00",
      "cve": "CVE-2026-11721",
      "id": "CVE-2026-11721",
      "initial_release_date": "2026-07-22T00:00:00+00:00",
      "product_status:known_affected": "82",
      "product_status:known_not_affected": "5",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "bind: bind9: Cache poisoning via label count discrepancy, RRSIG, wildcards",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-11721.json",
      "version": "3"
    }
  }
}



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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


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