# CVE-2026-116272: MIME-tools MIME::Parser duplicate boundary detection bypass with comments

Source: https://junglewise.ai/threats/cve-2026-116272-mime-field-paramval-versions-before-5-521-for-perl-do-not-flag-a  
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-2026-116272 · Severity: info · Published 2026-10-28

MIME-tools is a Perl library for parsing email messages. A flaw in versions before 5.521 allows attackers to bypass content filters by hiding attachments using a malformed boundary parameter containing nested comments. An attacker can send a crafted email where a filter checking for problematic content sees one version, but the recipient's mail client displays a different version with hidden attachments.

Technologies: [Perl MIME-tools](https://junglewise.ai/threats/technologies/mime-tools). Vendors: [Perl](https://junglewise.ai/threats/vendors/perl).

## Quick answers

**Is CVE-2026-116272 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-116272 being exploited in the wild.

**How severe is CVE-2026-116272?** Informational severity, published 28 October 2026.

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

**Is there a fix for CVE-2026-116272?** Yes: fixed in 5.521. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-116272 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-116272?** Check whether you run Perl 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 5.521

## Technical details

MIME::Parser fails to normalize boundary parameter names containing RFC 5322 comments (nested parentheses), storing them under literal names like "boundary((c))" instead of "boundary". This allows a second boundary parameter to evade duplicate detection. Readers that correctly strip comments parse the first boundary, while the parser sees an undetected second one, creating message-splitting ambiguity. An attacker exploits this via network delivery of a crafted MIME message to bypass ambiguous_content() checks.

## Affected products

- Perl 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)

## Related threats

- [MIME-tools FileUnder symlink following directory reuse](https://junglewise.ai/threats/cve-2026-116271-mime-parser-fileunder-versions-before-5-521-for-perl-reuse-a-pre)
- [MIME-tools RFC 2231 language tag parsing empty filename](https://junglewise.ai/threats/cve-2026-116269-mime-field-paramval-versions-before-5-521-for-perl-turn-an-rfc)
- [MIME-tools ParamVal regex backtracking CPU exhaustion](https://junglewise.ai/threats/cve-2026-116268-mime-field-paramval-versions-before-5-521-for-perl-allow-cpu)
- [MIME::tools RFC 2231 boundary ambiguity check bypass](https://junglewise.ai/threats/cve-2026-116265-mime-field-paramval-versions-before-5-521-for-perl-do-not-flag)