# CVE-2026-116270: libmime-tools-perl: MIME::Words versions before 5.521 for Perl allow memory exhaustion via repeated "=?" sequences in decode_mimewords

CVE-2026-116270 is fixed in 2 products on 1 platform, first by DEBIAN-CVE-2026-116270, released November 3, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-116270
- Priority: High
- CVSS: 7.5 (high)
- EPSS: 0.0029
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 22, 2026

## Description

MIME::Words versions before 5.521 for Perl allow memory exhaustion via repeated "=?" sequences in decode_mimewords.  For each "=?" that does not start a complete encoded word, decode_mimewords appends an error message containing the whole input string to $@. A boundary of 8,000 "=?" pairs (16,000 bytes) adds 8,000 copies of itself to $@, about 128 MB.  From version 5.518, MIME::Parser decodes every multipart boundary this way, so a remote sender can exhaust the memory of the parsing process with one Content-Type header.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | libmime-tools-perl Debian 14 | 5.522-1 | [DEBIAN-CVE-2026-116270](https://patchblox.com/security/data/fix/linux/debian-cve-2026-116270.md) | Nov 3, 2026 |
| Linux | perl-MIME-tools Fedora 43 | 5.522-1.fc43 | [FEDORA-2026-A415B3BF48](https://patchblox.com/security/data/fix/linux/fedora-2026-a415b3bf48.md) | Nov 7, 2026 |
| Linux | perl-MIME-tools opensuse-leap 16.0 | 5.522.0-bp160.1.1 | [OPENSUSE-SU-2026:22226-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-22226-1.md) | Nov 7, 2026 |

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Data as of 2026-11-09T13:31:49Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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