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Category:   Application (VPN)  >   OpenSSL Vendors:
OpenSSL DH Parameter Processing Lets Remote Servers Deny Service on Connected Clients
SecurityTracker Alert ID:  1041090
SecurityTracker URL:
CVE Reference:   CVE-2018-0732   (Links to External Site)
Date:  Jun 12 2018
Impact:   Denial of service via network
Fix Available:  Yes  Vendor Confirmed:  Yes  

Description:   A vulnerability was reported in OpenSSL. A remote user can cause denial of service conditions on the target system.

A remote server can return a large DH parameter prime value to the connected client during key agreement in a TLS handshake using a DH(E) based cipher suite to cause the client to hang while spending a long period of time generating a key for this prime.

The vendor was notified on June 5, 2018.

Guido Vranken reported this vulnerability.

Impact:   A remote server can cause denial of service conditions on the connected client.
Solution:   The vendor has issued a source code fix in commit ea7abeeab (for 1.1.0) and commit 3984ef0b7 (for 1.0.2).

The fix will be included in future versions 1.1.0i and 1.0.2p.

The vendor advisory is available at:

Vendor URL: (Links to External Site)
Cause:   Resource error
Underlying OS:  Linux (Any), UNIX (Any), Windows (Any)

Message History:   None.

 Source Message Contents

Subject:  [openssl-announce] OpenSSL Security Advisory

Hash: SHA512

OpenSSL Security Advisory [12 June 2018]

Client DoS due to large DH parameter (CVE-2018-0732)

Severity: Low

During key agreement in a TLS handshake using a DH(E) based ciphersuite a
malicious server can send a very large prime value to the client. This will
cause the client to spend an unreasonably long period of time generating a key
for this prime resulting in a hang until the client has finished. This could be
exploited in a Denial Of Service attack.

Due to the low severity of this issue we are not issuing a new release of
OpenSSL 1.1.0 or 1.0.2 at this time. The fix will be included in OpenSSL 1.1.0i
and OpenSSL 1.0.2p when they become available. The fix is also available in
commit ea7abeeab (for 1.1.0) and commit 3984ef0b7 (for 1.0.2) in the OpenSSL git

This issue was reported to OpenSSL on 5th June 2018 by Guido Vranken who also
developed the fix.


URL for this Security Advisory:

Note: the online version of the advisory may be updated with additional details
over time.

For details of OpenSSL severity classifications please see:

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