File 0003-Fix-potential-double-free-in-x509-alt-username-CVE-2.patch of Package openvpn.15874

From 1dde0cd6e5e6a0f2f45ec9969b7ff1b6537514ad Mon Sep 17 00:00:00 2001
From: Steffan Karger <steffan.karger@fox-it.com>
Date: Mon, 19 Jun 2017 11:28:40 +0200
Subject: [PATCH 3/5] Fix potential double-free in --x509-alt-username
 (CVE-2017-7521)

We didn't check the return value of ASN1_STRING_to_UTF8() in
extract_x509_extension().  Ignoring such a failure could result in buf
being free'd twice.  An error in ASN1_STRING_to_UTF8() can be caused
remotely if the peer can make the local process run out of memory.

The problem can only be triggered for configurations that use the
--x509-alt-username option with an x509 extension (i.e. the option
parameter starts with "ext:").

This issue was discovered, analysed and reported to the OpenVPN team by
Guido Vranken.

Extensive testing by Guido Vranken gives confidence that this function
is very unlikely to fail in real-world usage (using subjectAltName or
issuerAltName extensions) for other reasons than memory exhaustion.

CVE: 2017-7521
Signed-off-by: Steffan Karger <steffan.karger@fox-it.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Acked-by: David Sommerseth <davids@openvpn.net>
Acked-by: Guido Vranken <guidovranken@gmail.com>
Message-Id: <1497864520-12219-6-git-send-email-steffan.karger@fox-it.com>
URL: https://www.mail-archive.com/search?l=mid&q=1497864520-12219-6-git-send-email-steffan.karger@fox-it.com
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit cb4e35ece4a5b70b10ef9013be3bff263d82f32b)
---
 src/openvpn/ssl_verify_openssl.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/openvpn/ssl_verify_openssl.c b/src/openvpn/ssl_verify_openssl.c
index ba18e683..2a892747 100644
--- a/src/openvpn/ssl_verify_openssl.c
+++ b/src/openvpn/ssl_verify_openssl.c
@@ -138,7 +138,10 @@ bool extract_x509_extension(X509 *cert, char *fieldname, char *out, int size)
           switch (name->type)
             {
               case GEN_EMAIL:
-                ASN1_STRING_to_UTF8((unsigned char**)&buf, name->d.ia5);
+                if (ASN1_STRING_to_UTF8((unsigned char **)&buf, name->d.ia5) < 0)
+                  {
+                    continue;
+                  }
                 if ( strlen (buf) != name->d.ia5->length )
                   {
                     msg (D_TLS_ERRORS, "ASN1 ERROR: string contained terminating zero");
-- 
2.13.1