Citrix XenServer Multiple Vulnerabilities (CTX212736)

Critical Nessus Plugin ID 91352

New! Vulnerability Priority Rating (VPR)

Tenable calculates a dynamic VPR for every vulnerability. VPR combines vulnerability information with threat intelligence and machine learning algorithms to predict which vulnerabilities are most likely to be exploited in attacks. Read more about what VPR is and how it's different from CVSS.

VPR Score: 9.2


The remote host is affected by multiple vulnerabilities.


The version of Citrix XenServer running on the remote host is affected by multiple vulnerabilities in the bundled versions of OpenSSL and QEMU :

- Multiple flaws exist in the bundled version of OpenSSL in the aesni_cbc_hmac_sha1_cipher() and aesni_cbc_hmac_sha256_cipher() functions that are triggered when the connection uses an AES-CBC cipher and AES-NI is supported by the server. A man-in-the-middle attacker can exploit these issues to conduct a padding oracle attack, resulting in the ability to decrypt the network traffic. (CVE-2016-2107)

- A remote code execution vulnerability exists in the bundled version of OpenSSL in the ASN.1 encoder component due to an underflow condition that occurs when attempting to encode the value zero represented as a negative integer. An unauthenticated, remote attacker can exploit this to corrupt memory, resulting in the execution of arbitrary code. (CVE-2016-2108)

- An out-of-bounds write error exists in the bundled version of QEMU in the vga_update_memory_access() function that is triggered when access nodes are changed after the register bank has been set. An attacker on the guest can exploit this to execute arbitrary code with the privileges of the host's QEMU process.

- An integer overflow condition exists in the bundled version of QEMU in the vbe_update_vgaregs() function that is triggered when setting certain VGA registers while in VBE mode. An attacker on the guest can exploit this to crash the host's QEMU process.


Apply the appropriate hotfix as referenced in the vendor advisory.

See Also

Plugin Details

Severity: Critical

ID: 91352

File Name: citrix_xenserver_CTX212736.nasl

Version: 1.9

Type: local

Family: Misc.

Published: 2016/05/27

Updated: 2018/07/06

Dependencies: 76770

Risk Information

Risk Factor: Critical

VPR Score: 9.2

CVSS v2.0

Base Score: 10

Temporal Score: 7.8

Vector: CVSS2#AV:N/AC:L/Au:N/C:C/I:C/A:C

Temporal Vector: CVSS2#E:POC/RL:OF/RC:C

CVSS v3.0

Base Score: 9.8

Temporal Score: 8.8

Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Temporal Vector: CVSS:3.0/E:P/RL:O/RC:C

Vulnerability Information

CPE: cpe:/a:citrix:xenserver

Required KB Items: Host/XenServer/version, Host/local_checks_enabled

Exploit Available: true

Exploit Ease: Exploits are available

Patch Publication Date: 2016/05/18

Vulnerability Publication Date: 2016/05/03

Reference Information

CVE: CVE-2016-2107, CVE-2016-2108, CVE-2016-3710, CVE-2016-3712

BID: 90314, 90316

EDB-ID: 39768