Vulnerability-Lookup

GHSA-VXVJ-6RHP-3PQQ

Vulnerability from github – Published: 2026-07-22 15:31 – Updated: 2026-07-22 15:31

Details

In Unbound 1.9.0 up to and including 1.25.1, when a DNSCrypt query is received over TCP, the routine that encrypts the reply in place fails to bound the reply length against the destination buffer size. The size clamp that protects the UDP path is not applied on the TCP path, so a reply larger than 65504 bytes is shifted forward by 48 bytes inside a buffer of capacity equal to 'msg-buffer-size', writing past the end of the heap allocation. A single malicious encrypted query crashes the resolver and lead to denial of service. This vulnerability needs Unbound to be compiled with DNSCrypt support ('--enable-dnscrypt') and the 'dnscrypt:' clause to be configured and enabled for the listening interfaces.

Severity

7.5 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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{
  "affected": [],
  "aliases": [
    "CVE-2026-40691"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-122"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-07-22T14:17:18Z",
    "severity": "HIGH"
  },
  "details": "In Unbound 1.9.0 up to and including 1.25.1, when a DNSCrypt query is received over TCP, the routine that encrypts the reply in place fails to bound the reply length against the destination buffer size. The size clamp that protects the UDP path is not applied on the TCP path, so a reply larger than 65504 bytes is shifted forward by 48 bytes inside a buffer of capacity equal to \u0027msg-buffer-size\u0027, writing past the end of the heap allocation. A single malicious encrypted query crashes the resolver and lead to denial of service. This vulnerability needs Unbound to be compiled with DNSCrypt support (\u0027--enable-dnscrypt\u0027) and the \u0027dnscrypt:\u0027 clause to be configured and enabled for the listening interfaces.",
  "id": "GHSA-vxvj-6rhp-3pqq",
  "modified": "2026-07-22T15:31:24Z",
  "published": "2026-07-22T15:31:24Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-40691"
    },
    {
      "type": "WEB",
      "url": "https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-40691.txt"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}

CVE-2026-40691 (GCVE-0-2026-40691)

Vulnerability from cvelistv5 – Published: 2026-07-22 13:04 – Updated: 2026-07-22 14:31

Title

Packet of death for DNSCrypt over TCP

Summary

Severity

7.5 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-07-22 14:30 UTC

CWE

CWE-122 - Heap-based Buffer Overflow
CWE-787 - Out-of-bounds Write

Assigner

NLnet Labs

References

1 reference

URL	Tags
https://www.nlnetlabs.nl/downloads/unbound/CVE-20…	vendor-advisory

Impacted products

1 product

Vendor	Product	Version
NLnet Labs	Unbound	Affected: 1.9.0 , < 1.25.2 (semver)

Date Public

2026-07-22 00:00

Credits

Qifan Zhang (Palo Alto Networks) Trung Nguyen (@everping, CyStack)

Show details on NVD website

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{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-40691",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-07-22T14:30:33.327603Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-07-22T14:31:26.565Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Unbound",
          "vendor": "NLnet Labs",
          "versions": [
            {
              "lessThan": "1.25.2",
              "status": "affected",
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            }
          ]
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      ],
      "credits": [
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          "lang": "en",
          "type": "finder",
          "value": "Qifan Zhang (Palo Alto Networks)"
        },
        {
          "lang": "en",
          "type": "finder",
          "value": "Trung Nguyen (@everping, CyStack)"
        }
      ],
      "datePublic": "2026-07-22T00:00:00.000Z",
      "descriptions": [
        {
          "lang": "en",
          "value": "In Unbound 1.9.0 up to and including 1.25.1, when a DNSCrypt query is received over TCP, the routine that encrypts the reply in place fails to bound the reply length against the destination buffer size. The size clamp that protects the UDP path is not applied on the TCP path, so a reply larger than 65504 bytes is shifted forward by 48 bytes inside a buffer of capacity equal to \u0027msg-buffer-size\u0027, writing past the end of the heap allocation. A single malicious encrypted query crashes the resolver and lead to denial of service. This vulnerability needs Unbound to be compiled with DNSCrypt support (\u0027--enable-dnscrypt\u0027) and the \u0027dnscrypt:\u0027 clause to be configured and enabled for the listening interfaces."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
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          },
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              "lang": "en",
              "type": "CWE"
            },
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              "cweId": "CWE-787",
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              "type": "CWE"
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      "providerMetadata": {
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        "orgId": "206fc3a0-e175-490b-9eaa-a5738056c9f6",
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        }
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          "lang": "en",
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          "time": "2026-05-18T00:00:00.000Z",
          "value": "Issue reported by Qifan Zhang"
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          "time": "2026-06-10T00:00:00.000Z",
          "value": "NLnet Labs shares patch with Qifan Zhang"
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          "time": "2026-06-13T00:00:00.000Z",
          "value": "Qifan Zhang verifies patch"
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          "time": "2026-06-30T00:00:00.000Z",
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          "lang": "en",
          "time": "2026-07-02T00:00:00.000Z",
          "value": "NLnet Labs shares patch with Trung Nguyen"
        },
        {
          "lang": "en",
          "time": "2026-07-02T00:00:00.000Z",
          "value": "Trung Nguyen suggests extra fixes"
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          "time": "2026-07-03T00:00:00.000Z",
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          "time": "2026-07-04T00:00:00.000Z",
          "value": "Trung Nguyen verifies patch"
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          "lang": "en",
          "time": "2026-07-22T00:00:00.000Z",
          "value": "Fixes released with version 1.25.2"
        }
      ],
      "title": "Packet of death for DNSCrypt over TCP",
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  "cveMetadata": {
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    "datePublished": "2026-07-22T13:04:35.410Z",
    "dateReserved": "2026-06-22T10:11:10.532Z",
    "dateUpdated": "2026-07-22T14:31:26.565Z",
    "state": "PUBLISHED"
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}

Sightings

Author	Source	Type	Date	Other

Nomenclature

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Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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GHSA-VXVJ-6RHP-3PQQ

CVE-2026-40691 (GCVE-0-2026-40691)

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