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Re: sendmail and starttls failing

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On Sun, 30 Jun 2024, Greg Wooledge wrote:

> On Sun, Jun 30, 2024 at 23:08:01 +0100, Tim Woodall wrote:
>> According to this
>> https://support.trustwave.com/kb/KnowledgebaseArticle10016.aspx
>>
>> bare CRs aren't allowed in emails but this has always worked.
>>
>> I'm only likely to have cron generating emails like this.
>>
>> Strange that this would have been changed in a stable release. It
>> doesn't seem to have been a security update.
>
> It looks like it's coming from this change:
>
> https://metadata.ftp-master.debian.org/changelogs//main/s/sendmail/sendmail_8.17.1.9-2+deb12u2_changelog
>
>  * Fix CVE-2023-51765 (Closes: #1059386):
>    sendmail allowed SMTP smuggling in certain configurations.
>    Remote attackers can use a published exploitation
>    technique to inject e-mail messages with a spoofed
>    MAIL FROM address, allowing bypass of an SPF protection
>    mechanism. This occurs because sendmail supports
>    <LF>.<CR><LF> but some other popular e-mail servers
>    do not. This is resolved with 'o' in srv_features.
>
> I don't know the details of how this leads to a security hole.
>
>

It might be - but the wording suggested that this is blocking bare <LF>
which isn't my problem - and also I'd assume this is header related.

The thing I'm seeing is <CR> in the body of the email - I had no idea
this was illegal - and I'm surprised that tools like cron don't do
something to avoid sending "illegal" emails. Indeed, even mail will do
so happily.

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sendmail and starttls failing Michael Grant <mgrant@grant.org> - 2024-06-30 18:00 +0200
  Re: sendmail and starttls failing Michael Grant <mgrant@grant.org> - 2024-06-30 18:40 +0200
    Re: sendmail and starttls failing Tim Woodall <debianuser@woodall.me.uk> - 2024-06-30 20:40 +0200
  Re: sendmail and starttls failing Tim Woodall <debianuser@woodall.me.uk> - 2024-06-30 23:30 +0200
    Re: sendmail and starttls failing Michael Grant <mgrant@grant.org> - 2024-06-30 23:40 +0200
      Re: sendmail and starttls failing Tim Woodall <debianuser@woodall.me.uk> - 2024-07-01 00:40 +0200
        Re: sendmail and starttls failing Tim Woodall <debianuser@woodall.me.uk> - 2024-07-01 11:30 +0200
          Re: sendmail and starttls failing Tim Woodall <debianuser@woodall.me.uk> - 2024-07-01 18:40 +0200
    Re: sendmail and starttls failing Tim Woodall <debianuser@woodall.me.uk> - 2024-07-01 00:10 +0200
      Re: sendmail and starttls failing Greg Wooledge <greg@wooledge.org> - 2024-07-01 00:20 +0200
        Re: sendmail and starttls failing Tim Woodall <debianuser@woodall.me.uk> - 2024-07-01 00:30 +0200
          Re: sendmail and starttls failing Mark Fletcher <mark27q1@gmail.com> - 2024-07-01 10:50 +0200
            Re: sendmail and starttls failing Tim Woodall <debianuser@woodall.me.uk> - 2024-07-01 11:20 +0200
            Re: sendmail and starttls failing Greg Wooledge <greg@wooledge.org> - 2024-07-01 13:30 +0200
        Re: sendmail and starttls failing Jeffrey Walton <noloader@gmail.com> - 2024-07-01 00:50 +0200
      Re: sendmail and starttls failing Jeffrey Walton <noloader@gmail.com> - 2024-07-01 00:50 +0200

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