VulnerabilityPublished 28 Oct 2026

CVE-2026-116268: MIME-tools (Perl module) · ReDoS

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

Not known to be exploited : upgrade to 5.521 soon.

Data as of 28 Oct 2026, 17:57 UTC

Severity

High

Rated High 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

Upgrade to MIME::Field::ParamVal version 5.521 or later, where this inefficient regular expression complexity issue is fixed. No other mitigation is indicated or required.

Description

CVE-2026-116268 is a vulnerability in MIME::Field::ParamVal versions before 5.521 for Perl, where inefficient regular expression handling of unclosed comments in MIME header parameters can cause CPU exhaustion. Parsing a header with unclosed parentheses results in quadratic time complexity, significantly slowing processing. This issue is fixed in version 5.521.

Impact

This vulnerability can cause significant CPU resource exhaustion when processing crafted MIME headers with unclosed comments, potentially leading to denial of service conditions in applications using affected versions of MIME-tools. The parsing delay is quadratic relative to header size, which can severely degrade performance or availability.

Summary

The vulnerability arises from the comment pattern used to parse Content-Type and Content-Disposition parameters in MIME headers. Specifically, when a header parameter contains an opening parenthesis '(' without a corresponding closing parenthesis ')', the parser scans from each '(' to the end of the header repeatedly, causing parsing time to grow quadratically with header length. This parsing occurs multiple times per MIME entity on attribute lookups, amplifying the CPU load. For example, a 40 KB header can take approximately 7 seconds to parse once, leading to potential denial of service via CPU exhaustion. The flaw is resolved in MIME::Field::ParamVal version 5.521.

CWE-1333Inefficient Regular Expression Complexity (opens in a new tab)
Base weaknessLikelihood of exploit: High
The product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential.
Architecture and Design
Use regular expressions that do not support backtracking, e.g. by removing nested quantifiers.
System Configuration
Set backtracking limits in the configuration of the regular expression implementation, such as PHP's pcre.backtrack_limit. Also consider limits on execution time for the process.
Implementation
Do not use regular expressions with untrusted input. If regular expressions must be used, avoid using backtracking in the expression.
OWASP Cheat Sheets
File Upload (opens in a new tab)
OWASP ASVS 4.0.3
V12.1.1 (opens in a new tab)
Attack patterns
Regular Expression Exponential Blowup (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-1333

Technical details

References

Community reviews

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