Tobias Brunner found an authentication bypass vulnerability in strongSwan, an IKE/IPsec suite.

Due to insufficient validation of its local state the server implementation of the EAP-MSCHAPv2 protocol in the eap-mschapv2 plugin can be tricked into successfully concluding the authentication without providing valid credentials.

It's possible to recognize such attacks by looking at the server logs.
The following log message would be seen during the client authentication :

EAP method EAP_MSCHAPV2 succeeded, no MSK established

The strongswan package was updated to fix the following security issue :

  - CVE-2015-8023: Fixed an authentication bypass     vulnerability in the eap-mschapv2 plugin (bsc#953817).

Tobias Brunner found an authentication bypass vulnerability in strongSwan, an IKE/IPsec suite.

Due to insufficient validation of its local state the server implementation of the EAP-MSCHAPv2 protocol in the eap-mschapv2 plugin can be tricked into successfully concluding the authentication without providing valid credentials.

It's possible to recognize such attacks by looking at the server logs.
The following log message would be seen during the client authentication :

EAP method EAP_MSCHAPV2 succeeded, no MSK established

NOTE: Tenable Network Security has extracted the preceding description block directly from the DLA security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

According to the versions of the strongimcv package installed, the EulerOS installation on the remote host is affected by the following vulnerabilities :

  - The gmp plugin in strongSwan before 5.7.1 has a Buffer     Overflow via a crafted certificate.(CVE-2018-17540)

  - In verify_emsa_pkcs1_signature() in     gmp_rsa_public_key.c in the gmp plugin in strongSwan     4.x and 5.x before 5.7.0, the RSA implementation based     on GMP does not reject excess data in the     digestAlgorithm.parameters field during PKCS#1 v1.5     signature verification. Consequently, a remote attacker     can forge signatures when small public exponents are     being used, which could lead to impersonation when only     an RSA signature is used for IKEv2 authentication. This     is a variant of CVE-2006-4790 and     CVE-2014-1568.(CVE-2018-16152)

  - In verify_emsa_pkcs1_signature() in     gmp_rsa_public_key.c in the gmp plugin in strongSwan     4.x and 5.x before 5.7.0, the RSA implementation based     on GMP does not reject excess data after the encoded     algorithm OID during PKCS#1 v1.5 signature     verification. Similar to the flaw in the same version     of strongSwan regarding digestAlgorithm.parameters, a     remote attacker can forge signatures when small public     exponents are being used, which could lead to     impersonation when only an RSA signature is used for     IKEv2 authentication.(CVE-2018-16151)

  - strongSwan 5.6.0 and older allows Remote Denial of     Service because of Missing Initialization of a     Variable.(CVE-2018-10811)

  - The gmp plugin in strongSwan before 5.5.3 does not     properly validate RSA public keys before calling     mpz_powm_sec, which allows remote peers to cause a     denial of service (floating point exception and process     crash) via a crafted certificate.(CVE-2017-9022)

  - The gmp plugin in strongSwan before 5.6.0 allows remote     attackers to cause a denial of service (NULL pointer     dereference and daemon crash) via a crafted RSA     signature.(CVE-2017-11185)

  - The server implementation of the EAP-MSCHAPv2 protocol     in the eap-mschapv2 plugin in strongSwan 4.2.12 through     5.x before 5.3.4 does not properly validate local     state, which allows remote attackers to bypass     authentication via an empty Success message in response     to an initial Challenge message.(CVE-2015-8023)

  - strongSwan 4.3.0 through 5.x before 5.3.2 and     strongSwan VPN Client before 1.4.6, when using EAP or     pre-shared keys for authenticating an IKEv2 connection,     does not enforce server authentication restrictions     until the entire authentication process is complete,     which allows remote servers to obtain credentials by     using a valid certificate and then reading the     responses.(CVE-2015-4171)

Note that Tenable Network Security has extracted the preceding description block directly from the EulerOS security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

The strongswan package was updated to fix the following security issue :

  - CVE-2015-8023: Fixed an authentication bypass     vulnerability in the eap-mschapv2 plugin (bsc#953817).

Note that Tenable Network Security has extracted the preceding description block directly from the SUSE security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

The remote Ubuntu 14.04 LTS host has packages installed that are affected by a vulnerability as referenced in the USN-2811-1 advisory.

    It was discovered that the strongSwan eap-mschapv2 plugin incorrectly handled state. A remote attacker     could use this issue to bypass authentication.

Tenable has extracted the preceding description block directly from the Ubuntu security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

Strongswan Release Notes reports :

Fixed an authentication bypass vulnerability in the eap-mschapv2 plugin that was caused by insufficient verification of the internal state when handling MSCHAPv2 Success messages received by the client.
This vulnerability has been registered as CVE-2015-8023.

According to its self-reported version number, the remote pfSense install is prior to 2.2.6. It is, therefore, affected by multiple vulnerabilities.

ID	Name	Product	Family	Published	Updated	Severity
86888	Debian DSA-3398-1 : strongswan - security update	Nessus	Debian Local Security Checks	11/17/2015	1/11/2021	medium
87083	openSUSE Security Update : strongswan (openSUSE-2015-810)	Nessus	SuSE Local Security Checks	11/30/2015	1/19/2021	medium
86953	Debian DLA-345-1 : strongswan security update	Nessus	Debian Local Security Checks	11/20/2015	1/11/2021	medium
146695	EulerOS 2.0 SP2 : strongimcv (EulerOS-SA-2021-1364)	Nessus	Huawei Local Security Checks	2/22/2021	2/24/2021	high
87201	SUSE SLED12 / SLES12 Security Update : strongswan (SUSE-SU-2015:2183-1)	Nessus	SuSE Local Security Checks	12/4/2015	1/6/2021	medium
86896	Ubuntu 14.04 LTS : strongSwan vulnerability (USN-2811-1)	Nessus	Ubuntu Local Security Checks	11/17/2015	8/27/2024	critical
87202	SUSE SLED11 / SLES11 Security Update : strongswan (SUSE-SU-2015:2186-1)	Nessus	SuSE Local Security Checks	12/4/2015	1/6/2021	medium
86889	FreeBSD : strongswan -- authentication bypass vulnerability in the eap-mschapv2 plugin (3eb0ccc2-8c6a-11e5-8519-005056ac623e)	Nessus	FreeBSD Local Security Checks	11/17/2015	1/6/2021	medium
87645	SUSE SLED12 / SLES12 Security Update : strongswan (SUSE-SU-2015:2183-2)	Nessus	SuSE Local Security Checks	12/29/2015	1/6/2021	medium
106498	pfSense < 2.2.6 Multiple Vulnerabilities (SA-15_09 / SA-15_10 / SA-15_11)	Nessus	Firewalls	1/31/2018	11/8/2019	critical

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