From 5774cf4c25e1d8bf4e544702db8f157f111c9d93 Mon Sep 17 00:00:00 2001 From: Steffan Karger Date: Tue, 9 May 2017 21:30:08 +0200 Subject: [PATCH] Don't assert out on receiving too-large control packets (CVE-2017-7478) Commit 3c1b19e0 changed the maximum size of accepted control channel packets. This was needed for crypto negotiation (which is needed for a nice transition to a new default cipher), but exposed a DoS vulnerability. The vulnerability was found during the OpenVPN 2.4 code audit by Quarkslab (commisioned by OSTIF). To fix the issue, we should not ASSERT() on external input (in this case the received packet size), but instead gracefully error out and drop the invalid packet. CVE: 2017-7478 Signed-off-by: Steffan Karger Acked-by: David Sommerseth Message-Id: <1494358209-4568-2-git-send-email-steffan.karger@fox-it.com> URL: http://www.mail-archive.com/search?l=mid&q=1494358209-4568-2-git-send-email-steffan.karger@fox-it.com Signed-off-by: David Sommerseth --- Changes.rst | 8 ++++++++ src/openvpn/ssl.c | 7 ++++++- 2 files changed, 14 insertions(+), 1 deletion(-) diff --git a/Changes.rst b/Changes.rst index 3dba7e0e..734ef731 100644 --- a/Changes.rst +++ b/Changes.rst @@ -327,3 +327,11 @@ Bugfixes -------- - Fix memory leak introduced in 2.4.1: if --remote-cert-tls is used, we leaked some memory on each TLS (re)negotiation. + +Security +-------- +- Fix a pre-authentication denial-of-service attack on both clients and servers. + By sending a too-large control packet, OpenVPN 2.4.0 or 2.4.1 can be forced + to hit an ASSERT() and stop the process. If ``--tls-auth`` or ``--tls-crypt`` + is used, only attackers that have the ``--tls-auth`` or ``--tls-crypt`` key + can mount an attack. (OSTIF/Quarkslab audit finding 5.1, CVE-2017-7478) diff --git a/src/openvpn/ssl.c b/src/openvpn/ssl.c index 5f290fef..21c9d6f7 100644 --- a/src/openvpn/ssl.c +++ b/src/openvpn/ssl.c @@ -3720,7 +3720,12 @@ tls_pre_decrypt(struct tls_multi *multi, /* Save incoming ciphertext packet to reliable buffer */ struct buffer *in = reliable_get_buf(ks->rec_reliable); ASSERT(in); - ASSERT(buf_copy(in, buf)); + if(!buf_copy(in, buf)) + { + msg(D_MULTI_DROPPED, + "Incoming control channel packet too big, dropping."); + goto error; + } reliable_mark_active_incoming(ks->rec_reliable, in, id, op); }