Medium [CVE-2026-116264] Security filter bypass via invalid Content-Type parameter
This medium-severity Red Hat Linux advisory covers CVE-2026-116264 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 allow one invalid Content-Type parameter to hide the parameters after it, including the multipart boundary. Parameter parsing stops at the first parameter whose name it cannot read, such as x:y=1 or a name containing an 8-bit byte, and drops every parameter after it.
When the boundary is among them, MIME::Parser keeps the multipart body as a single undecoded part without marking the parse as ambiguous. Mail readers that skip the invalid parameter still find the boundary.
A remote sender can hide 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.
This vulnerability allows a remote attacker to bypass email security filters by sending an email with a malformed Content-Type parameter. Because the parser halts processing upon encountering an invalid parameter name, it discards subsequent parameters, including the multipart boundary, without flagging the content as ambiguous.
Consequently, security scanners fail to inspect concealed attachments that downstream email clients still render 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-1286. Affected Red Hat products: Red Hat Enterprise Linux 6.
Will not fix / out of support: 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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