VulnerabilityPublished 28 Oct 2026

CVE-2026-116269: MIME-tools (Perl module) · Interpretation Conflict

Affects MIME-tools (Perl module)Source CVE Database V5

Not known to be exploited : upgrade to 5.521 when convenient.

Data as of 28 Oct 2026, 17:57 UTC

Severity

Medium

Rated Medium by Threat Radar's AI analysis · CVSS not yet scored by NVD

Patch: Available – fixed in 5.521

Exploitation evidence

Disclosed: evidence found.
CVE published 28 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade MIME-tools (Perl module) to 5.521.

Affected software

Product	Affected	Fixed in
MIME-tools	Affected <5.521	Fixed in 5.521
CPANMIME-tools`pkg:cpan/MIME-tools`Other threats	Affected <5.521	Fixed in 5.521

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A fix is available in MIME-tools version 5.521. Users should upgrade to version 5.521 or later to resolve this issue. No other mitigation is indicated by the vendor advisory.

Description

CVE-2026-116269 is a vulnerability in MIME::Field::ParamVal versions before 5.521 for Perl where an RFC 2231 filename with a hyphenated language tag is incorrectly parsed, resulting in an empty recommended filename. This occurs because the decoder fails to strip the language suffix when it contains a hyphen, causing the recommended_filename() method to return an empty string instead of the actual filename. This behavior differs from other mail readers that correctly return the filename. A remote attacker can exploit this to bypass file extension checks on attachments by causing the recommended filename to be empty.

Impact

The impact is that remote attackers can bypass file extension-based security policies on email attachments by exploiting the empty recommended filename returned by vulnerable versions of MIME::Field::ParamVal. This could allow delivery of potentially malicious attachments that would otherwise be blocked based on their file extension.

Summary

The vulnerability arises from MIME::Field::ParamVal incorrectly handling RFC 2231 encoded filenames with hyphenated language tags (e.g., filename*=utf-8'en-US'payload.exe). The decoder appends the language tag to the charset but only strips the suffix if it is a single word. Because 'en-US' is hyphenated, the charset becomes UTF-8*EN-US, which the decoder cannot resolve, resulting in an empty string. Consequently, the recommended_filename() method returns an empty string rather than falling back to the name parameter. This discrepancy allows a remote sender to bypass attachment file extension policies that rely on the recommended filename.

CWE-436Interpretation Conflict (opens in a new tab)
Class weaknessOWASP Top 10 A06:2025: Insecure Design (opens in a new tab)
Product A handles inputs or steps differently than Product B, which causes A to perform incorrect actions based on its perception of B's state.
OWASP Cheat Sheets
REST Assessment (opens in a new tab)
REST Security (opens in a new tab)
Cross-Site Request Forgery Prevention (opens in a new tab)
Secure Design Principles (opens in a new tab)
OWASP ASVS 4.0.3
V13.2.5 (opens in a new tab)
Attack patterns
HTTP Request Splitting (opens in a new tab)
HTTP Response Smuggling (opens in a new tab)
HTTP Response Splitting (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

metacpan.org/release/DSKOLL/MIME-tools-5.521/changes (opens in a new tab)

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 28 Oct 2026, 17:46 UTC

WeaknessesCWE-436

Technical details

References

Community reviews

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