Vulnerability-Lookup

CVE-2026-80213 (GCVE-0-2026-80213)

Vulnerability from cvelistv5 – Published: 2026-08-27 14:22 – Updated: 2026-08-27 17:52

Summary

An issue was discovered in the resolv gem before 0.7.2 for Ruby. Resolv::DNS::MessageEncoder wrote a DNS label's length into a single octet without checking its range. A label longer than 255 octets had its length stored modulo 256 but the label data was written unchanged, and thus the bytes on the wire described a different name than the one the application asked to encode. RFC 1035 section 2.3.4 limits a label to 63 octets, and the two high bits of the length octet are reserved for compression pointers. put_string packed the length with put_pack("C", d.length) and put_label used it for labels, and thus any value from 0 to 255 could end up as a label length octet, including the reserved 0x40-0xBF range and the 0xC0-0xFF pointer range. Resolv::DNS::Name.create did not check per-label or total name length either, and thus an attacker-controlled hostname reached the encoder unchanged. An application that resolves an attacker-controlled hostname sends a query whose wire bytes name a domain the attacker chose. A hostname suffix that the application validates against an allowlist becomes padding that never appears on the wire, and thus allowlist and egress checks can be bypassed. The recursive resolver caches the response under the attacker's name, and DNS logs record that name rather than the one the application asked for. A label length whose low octet lands in the 0xC0-0xFF range produces a length octet that conforming parsers read as the start of a compression pointer, with the following attacker-controlled byte as the offset.

Severity

4 (Medium)


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

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-08-27 17:51 UTC

CWE

CWE-197 - Numeric Truncation Error

Assigner

mitre mitre root

References

2 references

URL	Tags
https://github.com/ruby/resolv
https://www.ruby-lang.org/en/news/2026/08/27/mult…

Impacted products

1 product

Vendor	Product	Version	CPE status
Ruby	resolv	Affected: 0 , < 0.3.2 (semver) Affected: 0.4.0 , < 0.7.2 (semver)	guessed

Show details on NVD website

JSON

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FKIE_CVE-2026-80213

Vulnerability from fkie_nvd - Published: 2026-08-27 17:20 - Updated: 2026-08-27 20:18

Severity

4.0 (Medium) - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N

Summary

References

	URL	Tags
	cve@mitre.org	https://github.com/ruby/resolv
	cve@mitre.org	https://www.ruby-lang.org/en/news/2026/08/27/multiple-vulnerabilities-in-resolv/

Impacted products

	Vendor	Product	Version

JSON

To clipboard

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  "affected": [
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      "affectedData": [
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          "defaultStatus": "unaffected",
          "packageURL": "pkg:gem/resolv",
          "product": "resolv",
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              "version": "0",
              "versionType": "semver"
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              "status": "affected",
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          ]
        }
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    }
  ],
  "id": "CVE-2026-80213",
  "lastModified": "2026-08-27T20:18:49.047",
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GHSA-JR95-X3FR-RCG4

Vulnerability from github – Published: 2026-08-27 18:32 – Updated: 2026-08-27 18:32

Details

Severity

4.0 (Medium)


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

Show details on source website

JSON

To clipboard

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  ],
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    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-08-27T17:20:51Z",
    "severity": "MODERATE"
  },
  "details": "An issue was discovered in the resolv gem before 0.7.2 for Ruby. Resolv::DNS::MessageEncoder wrote a DNS label\u0027s length into a single octet without checking its range. A label longer than 255 octets had its length stored modulo 256 but the label data was written unchanged, and thus the bytes on the wire described a different name than the one the application asked to encode. RFC 1035 section 2.3.4 limits a label to 63 octets, and the two high bits of the length octet are reserved for compression pointers. put_string packed the length with put_pack(\"C\", d.length) and put_label used it for labels, and thus any value from 0 to 255 could end up as a label length octet, including the reserved 0x40-0xBF range and the 0xC0-0xFF pointer range. Resolv::DNS::Name.create did not check per-label or total name length either, and thus an attacker-controlled hostname reached the encoder unchanged. An application that resolves an attacker-controlled hostname sends a query whose wire bytes name a domain the attacker chose. A hostname suffix that the application validates against an allowlist becomes padding that never appears on the wire, and thus allowlist and egress checks can be bypassed. The recursive resolver caches the response under the attacker\u0027s name, and DNS logs record that name rather than the one the application asked for. A label length whose low octet lands in the 0xC0-0xFF range produces a length octet that conforming parsers read as the start of a compression pointer, with the following attacker-controlled byte as the offset.",
  "id": "GHSA-jr95-x3fr-rcg4",
  "modified": "2026-08-27T18:32:25Z",
  "published": "2026-08-27T18:32:25Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-80213"
    },
    {
      "type": "WEB",
      "url": "https://github.com/ruby/resolv"
    },
    {
      "type": "WEB",
      "url": "https://www.ruby-lang.org/en/news/2026/08/27/multiple-vulnerabilities-in-resolv"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N",
      "type": "CVSS_V3"
    }
  ]
}

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.
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.

Action not permitted

CVE-2026-80213 (GCVE-0-2026-80213)

FKIE_CVE-2026-80213

GHSA-JR95-X3FR-RCG4

Tags

Sightings

Nomenclature