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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.

在 Ruby 的 库 0.7.2 版本之前发现了一个问题： 在写入 DNS 标签长度时，仅使用单个八位组（octet）存储，且未检查其取值范围。当标签长度超过 255 个八位组时，其长度会以模 256 的结果存储，但标签数据本身却原样写入。这导致网络传输中的字节所表示的域名名称与应用程序请求编码的名称不一致。 根据 RFC 1035 第 2.3.4 节，单个标签长度限制为 63 个八位组，而长度八位组的高两位保留用于压缩指针。 方法使用 打包长度， 方法将该值用于标签，因此 0 到 255 范围内的任何值都可能成为

CVSS 4.0 · Medium

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

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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