Medium [CVE-2026-116265] Security filter bypass via ambiguous multipart boundary continuations
This medium-severity Red Hat Linux advisory covers CVE-2026-116265 affecting Red Hat Enterprise Linux 6, Red Hat package: perl-mime-tools.
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Summary
MIME::Field::ParamVal versions before 5.521 for Perl do not flag an ambiguous multipart boundary written as RFC 2231 continuations. The boundary ambiguity checks look only at a plain boundary= parameter, and a boundary split into RFC 2231 sections (boundary*0=, boundary*1= and so on) is joined after they have run.
A repeated section number is concatenated rather than reported as a duplicate. From version 5.518, an encoded word or trailing whitespace in such a boundary also goes unflagged, although multipart_boundary() decodes or strips it.
A remote sender can make MIME::Parser split a message on a different boundary than other mail readers, hiding an attachment from a filter that relies on ambiguous_content() while the recipient's mail client shows it. A flaw was found in perl-MIME-tools.
A remote attacker can exploit this vulnerability to bypass email security filters by sending an email with specially crafted multipart boundary parameters.
Because the parser does not properly validate boundary parameters split across continuations, it processes message parts differently from standard email clients, allowing hidden attachments to evade inspection while still displaying to the recipient. Red Hat severity: Moderate — CVSS 5.3 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N).
Weakness: CWE-179. Affected Red Hat products: Red Hat Enterprise Linux 6.
- < 5.521
Official advisory · high-confidence parse· fetched 9 hours ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists. Confirm against the vendor advisory.
Official advisory · high-confidence parse· fetched 9 hours ago·verify at source
Mitigation
The source record does not include mitigation steps. That does not mean no fix exists. Read the vendor advisory below for the authoritative guidance.
Official advisory · high-confidence parse· fetched 9 hours ago·verify at source
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