CVE-2020-1967: proving sigalg != NULL

                							

                <!--X-Body-Begin-->
<!--X-User-Header-->
<a href="/fulldisclosure/"><img src="/images/fulldisclosure-logo.png" class="l-logo right" alt="fulldisclosure logo" width="80"></a>
<h2 class="m-list"><a href="/fulldisclosure/">Full Disclosure</a>
mailing list archives</h2>
<!--X-User-Header-End-->
<!--X-TopPNI-->
<div class="nav-bar">
<div class="nav-link">
<a href="4"><img src="/images/left-icon-16x16.png" alt="Previous" width="16" height="16"></a>
<a href="date.html#5">By Date</a>
<a href="6"><img src="/images/right-icon-16x16.png" alt="Next" width="16" height="16"></a>
</div>
<div class="nav-link">
<a href="4"><img src="/images/left-icon-16x16.png" alt="Previous" width="16" height="16"></a>
<a href="index.html#5">By Thread</a>
<a href="6"><img src="/images/right-icon-16x16.png" alt="Next" width="16" height="16"></a>
</div>
<form class="nst-search center" action="/search/fulldisclosure">
<input class="nst-search-q" name="q" type="search" placeholder="List Archive Search">
<button class="nst-search-button" title="Search">
<img style="width:100%;aspect-ratio:1/1;" alt="" aria-hidden="true" src="/shared/images/nst-icons.svg#search">
</button>
</form>

</div>

<!--X-TopPNI-End-->
<!--X-MsgBody-->
<!--X-Subject-Header-Begin-->
<h1 class="m-title">CVE-2020-1967: proving sigalg != NULL</h1>
<hr>
<!--X-Subject-Header-End-->
<!--X-Head-of-Message-->


<em>From</em>: Imre Rad &lt;radimre83 () gmail com&gt;


<em>Date</em>: Wed, 29 Apr 2020 19:39:31 +0200


<!--X-Head-of-Message-End-->
<!--X-Head-Body-Sep-Begin-->
<hr>
<!--X-Head-Body-Sep-End-->
<!--X-Body-of-Message-->
<pre style="margin: 0em;">I created a proof of concept exploit about the recent OpenSSL
signature_algorithms_cert DoS flaw (CVE-2020-1967). Credit for the
original finding goes to Bernd Edlinger.

This is a null pointer dereference while processing a crafted
signature_algorithms_cert TLS extension via the SSL_check_chain() API
method. Applications do need to call this method explicitly, it is not
invoked by default during the handshake. The segmentation fault of a
TLS service could look like this:

Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00007f09bcff3770 in tls1_check_sig_alg.part.0.cold () from
/data/openssl-1.1.1d/libssl.so
(gdb) bt
#0  0x00007f09bcff3770 in tls1_check_sig_alg.part.0.cold () from
/data/openssl-1.1.1d/libssl.so
#1  0x00007f09bd03f309 in tls1_check_chain () from
/data/openssl-1.1.1d/libssl.so
#2  0x00007f09bd403fc8 in set_cert_cb ()
#3  0x00007f09bd037f75 in tls_post_process_client_hello () from
/data/openssl-1.1.1d/libssl.so
#4  0x00007f09bd02703f in state_machine.part () from
/data/openssl-1.1.1d/libssl.so
#5  0x00007f09bcffa3f8 in ssl3_write_bytes () from
/data/openssl-1.1.1d/libssl.so
#6  0x00007f09bd00fbb9 in ssl_write_internal () from
/data/openssl-1.1.1d/libssl.so
#7  0x00007f09bd00fd07 in SSL_write () from /data/openssl-1.1.1d/libssl.so
#8  0x00007f09bd3e337d in sv_body ()
#9  0x00007f09bd40757a in do_server ()
#10 0x00007f09bd3e7c27 in s_server_main ()
#11 0x00007f09bd3cea46 in do_cmd ()
#12 0x00007f09bd3b89fd in main ()

This exploit relies on a patched version of openssl's s_client and can
be found here:

<a rel="nofollow" href="https://github.com/irsl/CVE-2020-1967">https://github.com/irsl/CVE-2020-1967</a>

_______________________________________________
Sent through the Full Disclosure mailing list
<a rel="nofollow" href="https://nmap.org/mailman/listinfo/fulldisclosure">https://nmap.org/mailman/listinfo/fulldisclosure</a>
Web Archives &amp; RSS: <a rel="nofollow" href="http://seclists.org/fulldisclosure/">http://seclists.org/fulldisclosure/</a>

</pre>
<!--X-Body-of-Message-End-->
<!--X-MsgBody-End-->
<!--X-Follow-Ups-->
<hr>
<!--X-Follow-Ups-End-->
<!--X-References-->
<!--X-References-End-->
<!--X-BotPNI-->
<div class="nav-bar">
<div class="nav-link">
<a href="4"><img src="/images/left-icon-16x16.png" alt="Previous" width="16" height="16"></a>
<a href="date.html#5">By Date</a>
<a href="6"><img src="/images/right-icon-16x16.png" alt="Next" width="16" height="16"></a>
</div>
<div class="nav-link">
<a href="4"><img src="/images/left-icon-16x16.png" alt="Previous" width="16" height="16"></a>
<a href="index.html#5">By Thread</a>
<a href="6"><img src="/images/right-icon-16x16.png" alt="Next" width="16" height="16"></a>
</div>
</div>
<h3 class="m-thread">Current thread:</h3>
<ul class="thread">
<li><strong>CVE-2020-1967: proving sigalg != NULL</strong> <em>Imre Rad (May 01)</em>
</li></ul>


<!--X-BotPNI-End-->
<!--X-User-Footer-->
<!--X-User-Footer-End-->
<p>