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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.

Mikel Lindsaar Mail是Mikel Lindsaar个人开发者开源的一个邮件处理库。 Mikel Lindsaar Mail 2.9.1之前版本存在处理逻辑错误漏洞，该漏洞源于解码函数使用单个String#match和过度贪婪的字符集捕获，仅解码第一个RFC 2047编码词并错误处理周围或后续文本，特制畸形编码词可能跨越?分隔符，导致解码后的From、To或Reply-To头值与原始值不同，进而实现发件人或收件人欺骗、钓鱼攻击或授权检查绕过。

CVSS 5.3 · Medium EPSS 0.45% · P39

Possible ATT&CK Techniques 1 AI

T1565.001 · Stored Data Manipulation

Affected Version Matrix 1

VendorProduct Version RangeStatus
mikel mail < 2.9.1 affected
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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
Vulnerability Title
Mikel Lindsaar Mail 处理逻辑错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Mikel Lindsaar Mail是Mikel Lindsaar个人开发者开源的一个邮件处理库。 Mikel Lindsaar Mail 2.9.1之前版本存在处理逻辑错误漏洞，该漏洞源于解码函数使用单个String#match和过度贪婪的字符集捕获，仅解码第一个RFC 2047编码词并错误处理周围或后续文本，特制畸形编码词可能跨越?分隔符，导致解码后的From、To或Reply-To头值与原始值不同，进而实现发件人或收件人欺骗、钓鱼攻击或授权检查绕过。
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
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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Patches & Fixes for CVE-2026-63435 (2)

Vendor Advisories for CVE-2026-63435 (1)

Vendor Pages for CVE-2026-63435 (1)

IV. Related Vulnerabilities

Same weakness: CWE-436