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Vulnerability · Published Oct 28, 2026 · Assigned by CPANSec

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

High 7.5

In plain English

A high-severity security flaw in MIME-tools. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 22% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.5High
Exploit odds (30 days)0.3%top 78.2% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:12libmime-tools-perlno fix listedDEBIAN-CVE-2026-116270
Debian:13libmime-tools-perlno fix listedDEBIAN-CVE-2026-116270
Debian:14libmime-tools-perl5.522-1DEBIAN-CVE-2026-116270
Ubuntu:22.04:LTSlibmime-tools-perlno fix listedUBUNTU-CVE-2026-116270
Ubuntu:24.04:LTSlibmime-tools-perlno fix listedUBUNTU-CVE-2026-116270
Ubuntu:26.04:LTSlibmime-tools-perlno fix listedUBUNTU-CVE-2026-116270
Ubuntu:26.10libmime-tools-perlno fix listedUBUNTU-CVE-2026-116270

Affected products (as reported)

VendorProductVersions
MIME-tools 0 – before 5.521

Weakness: CWE-407 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References