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CVE-2026-80213

Quick assessment

Affected
Ruby resolv
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Ruby Resolv是Ruby组织的一个用 Ruby 编写的线程感知型 DNS 解析器库。 Ruby Resolv 0.7.2之前版本存在数字错误漏洞，该漏洞源于Resolv::DNS::MessageEncoder在写入DNS标签长度时未检查其范围，可能导致绕过允许列表和出口检查。

CVSS 4.0 · Medium EPSS 0.35% · P27

Possible ATT&CK Techniques 1 AI

T1071 · Application Layer Protocol

Affected Version Matrix 2

VendorProduct Version RangeStatus
Ruby resolv < 0.3.2 affected
0.4.0< 0.7.2 affected
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I. Basic Information for CVE-2026-80213

Vulnerability Information
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Vulnerability Title
N/A
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
数值截断错误
Source: CVE Program / CVE List V5
Vulnerability Title
Ruby Resolv 数字错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Ruby Resolv是Ruby组织的一个用 Ruby 编写的线程感知型 DNS 解析器库。 Ruby Resolv 0.7.2之前版本存在数字错误漏洞，该漏洞源于Resolv::DNS::MessageEncoder在写入DNS标签长度时未检查其范围，可能导致绕过允许列表和出口检查。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Ruby resolv 0 ~ 0.3.2 -

II. Public POCs for CVE-2026-80213

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III. Intelligence Information for CVE-2026-80213

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Vendor Advisories for CVE-2026-80213 (1)

Proof of Concept for CVE-2026-80213 (1)

IV. Related Vulnerabilities

Same product: resolv
Same vendor: Ruby
Same weakness: CWE-197

V. Comments for CVE-2026-80213

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