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CVE-2026-63435— Mail: Email address spoofing via malformed RFC 2047 encoded-words

Quick assessment

Affected
mikel mail
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.

邮件（Mail） 是一个用于 Ruby 的互联网库，旨在处理电子邮件的生成、解析和发送。在 2.9.1 版本之前， 和 在处理 RFC 2047 编码字解码时，使用了单个 以及过于贪婪的字符集捕获逻辑，导致只能正确解码第一个 RFC 2047 编码字，并对前后相邻或后续文本的处理出现错误。 攻击者可以构造一个格式异常的编码字，嵌入在地址的显示名（display name）或本地部分中，使其跨越 分隔符，从而导致解码后的 、 或 头部的值与人类审查者或下游解析器所查看的原始值不一致。这种不一致可能引发发件人或收件人伪

CVSS 5.3 · Medium

Possible ATT&CK Techniques 1 AI

T1565.001 · Stored Data Manipulation
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I. Basic Information for CVE-2026-63435

Vulnerability Information
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Vulnerability Title
Mail: Email address spoofing via malformed RFC 2047 encoded-words
Source: CVE Program / CVE List V5
Vulnerability Description
Mail is an internet library for Ruby designed to handle email generation, parsing, and sending. Prior to 2.9.1, Mail::Utilities.q_value_decode and Mail::Utilities.b_value_decode used a single String#match and an overly greedy charset capture to decode only the first RFC 2047 encoded-word and mishandle surrounding or subsequent text. A crafted malformed encoded-word in an address display name or local part could cross ? delimiters and make decoded From, To, or Reply-To header values differ from the raw values inspected by a human reviewer or downstream parser, enabling apparent sender or recipient spoofing, phishing, or authorization-check bypass. This issue is fixed in version 2.9.1.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
解释冲突
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
mikel mail < 2.9.1 -

II. Public POCs for CVE-2026-63435

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III. Intelligence Information for CVE-2026-63435

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Other References for CVE-2026-63435 (4)

IV. Related Vulnerabilities

Same weakness: CWE-436

V. Comments for CVE-2026-63435

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