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Fix garbled non-MIME-encoded UTF-8 headers #10078

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Fix garbled non-MIME-encoded UTF-8 headers #10078

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5 changes: 5 additions & 0 deletions program/lib/Roundcube/rcube_mime.php
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Original file line number Diff line number Diff line change
Expand Up @@ -162,6 +162,11 @@ public static function decode_mime_string($input, $fallback = null)
{
$default_charset = $fallback ?: self::get_charset();

// RFC 6532: detect raw UTF-8 in headers to avoid wrong charset conversion
if ($fallback !== false && mb_check_encoding($input, 'UTF-8') && preg_match('/[\x80-\xFF]/', $input)) {

@alecpl alecpl Mar 15, 2026

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You should not assume RCUBE_CHARSET is always UTF-8.

@OctopusET OctopusET Mar 15, 2026

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Then should we change to

$default_charset = 'UTF-8';

instead?

@OctopusET OctopusET May 8, 2026

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I have rebased and applied that part.

@OctopusET OctopusET May 8, 2026

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for that I had to force push, sorry if it made you inconvenient

$default_charset = 'UTF-8';
}

// rfc: all line breaks or other characters not found
// in the Base64 Alphabet must be ignored by decoding software
// delete all blanks between MIME-lines, differently we can
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17 changes: 17 additions & 0 deletions tests/Framework/MimeTest.php
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Expand Up @@ -216,6 +216,23 @@ public function test_header_decode_qp()
}
}

/**
* Test decoding of raw UTF-8 headers (RFC 6532)
* Uses rcube_mime::decode_mime_string()
*/
public function test_header_decode_raw_utf8()
{
// Raw UTF-8 Korean with wrong fallback charset - should be preserved
$korean = "\xEC\x95\x88\xEB\x85\x95\xED\x95\x98\xEC\x84\xB8\xEC\x9A\x94"; // 안녕하세요
$res = \rcube_mime::decode_mime_string($korean, 'ISO-8859-1');
$this->assertSame($korean, $res, 'Raw UTF-8 header with Latin-1 fallback');

// Latin-1 high bytes (not valid UTF-8) - should still be converted
$latin1 = "caf\xE9"; // café in ISO-8859-1
$res = \rcube_mime::decode_mime_string($latin1, 'ISO-8859-1');
$this->assertSame('café', $res, 'Latin-1 header should be converted');
}

/**
* Test headers parsing
*/
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