Ruby resolv up to 0.3.1/0.7.1 DNS Message Encoder MessageEncoder buffer size

Summaryinfo

A vulnerability described as problematic has been identified in Ruby resolv up to 0.3.1/0.7.1. This impacts the function Resolv::DNS::MessageEncoder of the component DNS Message Encoder. The manipulation results in buffer size. This vulnerability is known as CVE-2026-80213. It is possible to launch the attack remotely. No exploit is available.

Detailsinfo

A vulnerability was found in Ruby resolv up to 0.3.1/0.7.1. It has been classified as problematic. Affected is the function Resolv::DNS::MessageEncoder of the component DNS Message Encoder. The manipulation with an unknown input leads to a buffer size vulnerability. CWE is classifying the issue as CWE-131. The product does not correctly calculate the size to be used when allocating a buffer, which could lead to a buffer overflow. This is going to have an impact on integrity. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is traded as CVE-2026-80213 since 08/26/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. There are known technical details, but no exploit is available.

Upgrading to version 0.3.2 or 0.7.2 eliminates this vulnerability.

VulDB is the best source for vulnerability data and more expert information about this specific topic.

Productinfo

Type

• Programming Language Software

Vendor

• Ruby

Name

• resolv

Version

• 0.3.0
• 0.3.1
• 0.7.0
• 0.7.1

License

• open-source

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

VulDB is the best source for vulnerability data and more expert information about this specific topic.

Discussion