---
id: CVE-2026-80212
title: An issue was discovered in the resolv gem before 0.7.2 for Ruby
summary: >-
  An issue was discovered in the resolv gem before 0.7.2 for Ruby.
  Resolv::DNS::Resource.get_class, Resolv::DNS::Resource::Generic.create, and
  Resolv::DNS::SvcParam::Generic.create generate a new class for each unknown
  DNS resource record …
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-770
published: '2026-08-27'
updated: '2026-09-09'
sourceUpdated: '2026-09-09T16:04:24.933'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-80212'
references:
  - url: 'https://github.com/ruby/resolv'
    label: cve@mitre.org
  - url: >-
      https://www.ruby-lang.org/en/news/2026/08/27/multiple-vulnerabilities-in-resolv/
    label: cve@mitre.org
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-80212.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-80212'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2525066'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-80212'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-80212'
  - url: >-
      https://github.com/ruby/resolv/commit/6393c628b224d0234ef915813c0977e11ebe57ea
  - url: 'https://access.redhat.com/errata/RHSA-2026:57986'
  - url: 'https://access.redhat.com/errata/RHSA-2026:57994'
  - url: 'https://access.redhat.com/errata/RHSA-2026:57565'
tags:
  - nvd
  - csaf
  - vex
  - red-hat
epss: 0.00569
epssPercentile: 0.44717
ingestedAt: '2026-09-09T16:14:05.516Z'
vendor: Red Hat
product: Red Hat Enterprise Linux 8
affected:
  - lightspeed_core
  - enterprise_linux 10
  - enterprise_linux 6
  - enterprise_linux 7
  - enterprise_linux 8
  - enterprise_linux 9
  - hardened_images
patched:
  - hardened_images
---

## Overview

An issue was discovered in the resolv gem before 0.7.2 for Ruby. Resolv::DNS::Resource.get_class, Resolv::DNS::Resource::Generic.create, and Resolv::DNS::SvcParam::Generic.create generate a new class for each unknown DNS resource record (type, class) pair, or each unknown SvcParamKey, encountered while decoding a response. Each generated class was permanently registered both as a constant on Resource (or SvcParam::Generic) and as an entry in a class-lookup hash (ClassHash), and thus the class remained reachable through that constant after the response was discarded. Type and class are each 16-bit values, and thus an attacker controlling DNS responses (a spoofed response, or a malicious or hijacked upstream DNS server) has roughly 2^32 distinct (type, class) pairs to choose from. A single response of a few hundred kilobytes carrying tens of thousands of distinct unknown types permanently grows process memory by tens of megabytes; repeated responses accumulate without bound and are never reclaimed by garbage collection, because the constant keeps each class alive. Any code path that calls Resolv::DNS::Message.decode on attacker-influenced DNS responses is affected. resolv is a default gem, and thus this is reachable from a plain Ruby installation without any additional dependency.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Vendor advisories

- **RHSA-2026:57986** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-08-21 · [advisory](https://access.redhat.com/errata/RHSA-2026:57986)
- **RHSA-2026:57994** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-08-21 · [advisory](https://access.redhat.com/errata/RHSA-2026:57994)
- **RHSA-2026:57565** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-08-20 · [advisory](https://access.redhat.com/errata/RHSA-2026:57565)
- **Red Hat VEX** · Important · affected: Lightspeed Core, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9 · no fix planned: Red Hat Enterprise Linux 6, Lightspeed Core, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 7, … · updated 2026-09-17 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-80212.json)