Alternative chains certificate forgery (CVE-2015-1793)

Advisory ID	CVE Number	Date discovered	Severity	Advisory revision
STORM-2015-008	CVE-2015-1793	07/09/2015	high	v2

Vulnerability details

During certificate verification, OpenSSL attempts to find an alternative certificate chain if the first attempt to build such a chain fails. Because of an error of implementation of this process, an attacker could cause this flaw to bypass certain checks on untrusted certificates, such as the CA flag, enabling these checks to use a valid leaf certificate to act as a CA and “issue” an invalid certificate.

This issue will impact any application that verifies certificates including SSL/TLS/DTLS clients and SSL/TLS/DTLS servers using client authentication.

Impacted products

Products	Severity	Detail
Stormshield Network Security	high	SNS uses a vulnerable version of OpenSSL
Netasq	high	Netasq uses a vulnerable version of OpenSSL

Revisions

Version	Date	Description
v1	07/15/2015	Initial release
v2	07/27/2015	New workaround for SNS and Netasq

Stormshield Network Security

CVSS v2 Overall Score: 7.5

Analysis

Impacted version

Webadmin, authentication portal and ssl vpn portal are vulnerable because they use client certificate authentication.

SSL proxy can also trust malicious clients and servers.

SNS v1.0 to v1.3.3
SNS v2.1 to v2.1.1

Workaround solution

Solution

SSL client certificate authentication can be disabled in the Webadmin, authentication portal and ssl vpn.

There is no workaround solution for the ssl proxy.

The v1.3.4 and v2.1.2 will fix this vulnerability.

Access vector	Access complexity	Authentication	Confidentiality impact	Integrity impact	Availability impact
Network	Low	None	Partial	Partial	None

CVSS Base score: 6.4	CVSS Vector: (AV:N/AC:L/Au:N/C:P/I:P/A:N)

Exploitability	Remediation Level	Report Confidence
High	Unavailable	Confirmed

CVSS Temporal score: 6.4	CVSS Vector: (AV:N/AC:L/Au:N/C:P/I:P/A:N/E:H/RL:U/RC:C)

Collateral Damage Potential	Target Distribution
Low-Medium	High [76-100%]

CVSS Environmental score: 7.5	CVSS Vector: (AV:N/AC:L/Au:N/C:P/I:P/A:N/E:H/RL:U/RC:C/CDP:LM/TD:H/CR:ND/IR:ND/AR:ND)

Netasq