An issue was discovered in the resolv gem before 0.7.2 for Ruby

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
• RHSA-2026:57994 · Red Hat · fixed in: Red Hat Hardened Images · released 2026-08-21 · advisory
• RHSA-2026:57565 · Red Hat · fixed in: Red Hat Hardened Images · released 2026-08-20 · advisory
• 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