# CVE-2026-116264: MIME::tools parameter parsing information disclosure

Source: https://junglewise.ai/threats/cve-2026-116264-mime-field-paramval-versions-before-5-521-for-perl-allow-one  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-28. Updated: 2026-10-28  
License: CC BY 4.0 with a link back

CVE-2026-116264 · Severity: info · Published 2026-10-28

MIME::tools is a Perl library that parses email messages. An attacker can craft a malicious email with an invalid parameter in the Content-Type header that causes the parser to skip subsequent parameters, including the multipart boundary. This allows hidden attachments to be concealed from email security filters while remaining visible to the recipient's mail client, potentially bypassing threat detection.

Vendors: [CPAN](https://junglewise.ai/threats/vendors/cpan).

## Quick answers

**Is CVE-2026-116264 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-116264 being exploited in the wild.

**How severe is CVE-2026-116264?** Informational severity, published 28 October 2026.

**Which products and versions are affected?** CPAN MIME-tools before 5.521.

**Is there a fix for CVE-2026-116264?** Yes: fixed in MIME-tools 5.521. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-116264 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-116264?** Check whether you run CPAN MIME-tools at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in MIME-tools 5.521

## Technical details

The vulnerability exists in MIME::Field::ParamVal's parameter parsing logic, which stops reading parameters upon encountering an invalid parameter name (containing 8-bit bytes or malformed syntax like "x:y=1"). All parameters after the invalid one are dropped, including the multipart boundary. When the boundary is hidden, MIME::Parser treats the multipart body as a single undecoded part but does not flag the parse as ambiguous, creating a discrepancy with mail clients that skip the invalid parameter and locate the boundary.

## Affected products

- CPAN MIME-tools before 5.521

## Timeline

- 2026-10-28: disclosed
- 2026-10-27: patched

## References

- [https://cpan.org/modules](https://cpan.org/modules)
- [https://metacpan.org/release/DSKOLL/MIME-tools-5.521/changes](https://metacpan.org/release/DSKOLL/MIME-tools-5.521/changes)