CVE-2026-116266— MIME::Head versions from 5.518 before 5.521 for Perl decode a partly encoded multipart boundary without flagging the parse as ambiguous

Quick assessment

Affected

CVE-2026-116266

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.

Perl 的 MIME::Head 模块在 5.518 至 5.521（不含 5.521）版本中存在一个漏洞：当处理部分编码的多部分（multipart）边界时，该模块未能将解析结果标记为“存在歧义”。具体而言，方法会解码边界中任意位置的 RFC 2047 编码词，但歧义检测机制仅在边界值整体为一个编码词时才会触发。例如，边界会被解析为，而方法会错误地返回。由于 RFC 规定编码词不允许出现在参数中，其他邮件客户端会按字面值（即包含编码词的原始字符串）对邮件进行分割。因此，远程攻击者可以利用此漏洞，向

AI Predicted 6.5 Difficulty: Easy EPSS 0.18% · P7 Updated Oct 29, 2026

Possible ATT&CK Techniques 1 AI

T1056.002 · GUI Input Capture

Affected Version Matrix 1

Vendor	Product	Version Range	Status
None	None	`5.518< 5.521`	affected

Vulnerability Information

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Vulnerability Title

MIME::Head versions from 5.518 before 5.521 for Perl decode a partly encoded multipart boundary without flagging the parse as ambiguous

Source: CVE Program / CVE List V5

Vulnerability Description

MIME::Head versions from 5.518 before 5.521 for Perl decode a partly encoded multipart boundary without flagging the parse as ambiguous. The multipart_boundary() method decodes RFC 2047 encoded words anywhere in the boundary, but the ambiguity check only fires when the whole value is one encoded word. A boundary such as abc=?us-ascii?Q?def?= is used as abcdef, and ambiguous_content() returns false. Encoded words are not allowed in parameters, so other mail readers split the message on the literal value. A remote sender can hide an attachment from a filter that relies on ambiguous_content() while the recipient's mail client shows it.

Source: CVE Program / CVE List V5

CVSS Information

N/A

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
-	-	5.518 ~ 5.521	-

II. Public POCs for CVE-2026-116266

#	POC Description	Source Link	Shenlong Link

AI-Generated POC Premium

No public POC found.

III. Intelligence Information for CVE-2026-116266

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Other References for CVE-2026-116266 (1)

https://metacpan.org/release/DSKOLL/MIME-tools-5.521/changes release-notes

https://www.cve.org/CVERecord?id=CVE-2026-116266

IV. Related Vulnerabilities

Same weakness: CWE-436