Vulnerability-Lookup

GHSA-G479-FG97-PF5W

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

Details

In NLnet Labs Unbound 1.23.0 up to and including 1.25.1, when 'dns-error-reporting: yes' is set, the EDNS Report-Channel option (code 18) from the last upstream response is read and uses the option's length as the length of the agent domain. When a domain name check is performed on the agent domain, the returned lenght is not used and if the agent domain is followed by garbage, those bytes are moved onto the tail of the synthetic '_er.' report query name. That query name is later used in the iterator via a subquery to send out the DNS Error Report and when Unbound tries to walk that query name during 'find_closest_of_type()', it strips labels using the query name length rather than stopping at the embedded root, walks one byte past it, and feeds the first garbage byte to 'dname_query_hash()' as a label length writing over the stack variable 'labuf'. One ordinary upstream response from a delegated zone the attacker controls is sufficient to terminate the daemon.

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-2026-55973"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-20"
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    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-07-22T14:17:21Z",
    "severity": "HIGH"
  },
  "details": "In NLnet Labs Unbound 1.23.0 up to and including 1.25.1, when \u0027dns-error-reporting: yes\u0027 is set, the EDNS Report-Channel option (code 18) from the last upstream response is read and uses the option\u0027s length as the length of the agent domain. When a domain name check is performed on the agent domain, the returned lenght is not used and if the agent domain is followed by garbage, those bytes are moved onto the tail of the synthetic \u0027_er.\u0027 report query name. That query name is later used in the iterator via a subquery to send out the DNS Error Report and when Unbound tries to walk that query name during \u0027find_closest_of_type()\u0027, it strips labels using the query name length rather than stopping at the embedded root, walks one byte past it, and feeds the first garbage byte to \u0027dname_query_hash()\u0027 as a label length writing over the stack variable \u0027labuf\u0027. One ordinary upstream response from a delegated zone the attacker controls is sufficient to terminate the daemon.",
  "id": "GHSA-g479-fg97-pf5w",
  "modified": "2026-07-22T15:31:25Z",
  "published": "2026-07-22T15:31:25Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-55973"
    },
    {
      "type": "WEB",
      "url": "https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-55973.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-2026-55973 (GCVE-0-2026-55973)

Vulnerability from cvelistv5 – Published: 2026-07-22 13:09 – Updated: 2026-07-22 14:06

Title

'dns-error-reporting: yes' leads to stack buffer overflow

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 (v2.0.3)

CWE

CWE-20 - Improper Input Validation

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: 1.23.0 , < 1.25.2 (semver)

Date Public

2026-07-22 00:00

Credits

Qifan Zhang (Palo Alto Networks)

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JSON

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    "adp": [
      {
        "metrics": [
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                "id": "CVE-2026-55973",
                "options": [
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                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-07-22T14:05:39.964116Z",
                "version": "2.0.3"
              },
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          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
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      "descriptions": [
        {
          "lang": "en",
          "value": "In NLnet Labs Unbound 1.23.0 up to and including 1.25.1, when \u0027dns-error-reporting: yes\u0027 is set, the EDNS Report-Channel option (code 18) from the last upstream response is read and uses the option\u0027s length as the length of the agent domain. When a domain name check is performed on the agent domain, the returned lenght is not used and if the agent domain is followed by garbage, those bytes are moved onto the tail of the synthetic \u0027_er.\u0027 report query name. That query name is later used in the iterator via a subquery to send out the DNS Error Report and when Unbound tries to walk that query name during \u0027find_closest_of_type()\u0027, it strips labels using the query name length rather than stopping at the embedded root, walks one byte past it, and feeds the first garbage byte to \u0027dname_query_hash()\u0027 as a label length writing over the stack variable \u0027labuf\u0027. One ordinary upstream response from a delegated zone the attacker controls is sufficient to terminate the daemon."
        }
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          "time": "2026-05-29T00:00:00.000Z",
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          "time": "2026-05-30T00:00:00.000Z",
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          "time": "2026-07-22T00:00:00.000Z",
          "value": "Fixes released with version 1.25.2"
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    "state": "PUBLISHED"
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Sightings

Author	Source	Type	Date	Other

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.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
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.

Detection rules are retrieved from Rulezet.

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.

Action not permitted

GHSA-G479-FG97-PF5W

CVE-2026-55973 (GCVE-0-2026-55973)

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Sightings

Nomenclature