Re: [exim] CVE-2019-15846: Exim - local or remote attacker c…

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Author: Heiko Schlittermann
Date:  
To: exim-users
Subject: Re: [exim] CVE-2019-15846: Exim - local or remote attacker can execute programs with root privileges.
Dmitriy Matrosov via Exim-users <exim-users@???> (Sa 07 Sep 2019 10:39:20 CEST):
> >
> > And, if your Exim is linked against GnuTLS there is no $tls_sni variable
> > at all. But - to my knowledge - the exploitable string is written to the
> > -H spool file anyway (and read back).
>
> On Debian 7, 8, 9 (exim is linked against gnutls) and there is $tls_sni
> option. On Debian 8, 9 also there is $tls_in_sni option (as expected).


Thank you for pointing out. I should have been more specific. If you do
not have a $tls_in_sni, check if $tls_sni exists. Otherwise you may have
an Exim version not supporting this *variable*. This does not imply,
that you're not vulnerable.

The existence of this variable seems to have changed over the time,
in 4.80 it existed, in 4.84 it didn't exist for GnuTLS, in 4.89 it was
there again.

exim-4_80:src/src/expand.c
    #ifdef SUPPORT_TLS
    { "tls_sni",             vtype_stringptr,   &tls_sni },
    #endif


exim-4_84:src/src/expand.c
    #if defined(SUPPORT_TLS) && !defined(USE_GNUTLS)
    { "tls_in_sni",          vtype_stringptr,   &tls_in.sni },
    #endif
    …
    #if defined(SUPPORT_TLS) && !defined(USE_GNUTLS)
    { "tls_sni",             vtype_stringptr,   &tls_in.sni },    /* mind the alphabetical order! */
    #endif


exim-4_89:src/src/expand.c
    #if defined(SUPPORT_TLS)
    { "tls_in_sni",          vtype_stringptr,   &tls_in.sni },
    #endif
    …
    #if defined(SUPPORT_TLS)
    { "tls_sni",             vtype_stringptr,   &tls_in.sni },    /* mind the alphabetical order! */
    #endif



I checked the original source, and didn't check the versions in between.

    Best regards from Dresden/Germany
    Viele Grüße aus Dresden
    Heiko Schlittermann
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