CVE-2026-116270 Affecting libmime-tools-perl package, versions *

Note: Versions mentioned in the description apply only to the upstream libmime-tools-perl package and not the libmime-tools-perl package as distributed by Echo. See How to fix? for Echo:latest relevant fixed versions and status.

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.

• https://advisory.echohq.com/cve/CVE-2026-116270
• https://metacpan.org/release/DSKOLL/MIME-tools-5.521/changes