#VU9651 TLS Padding Oracle in Citrix NetScaler - CVE-2017-17382

Vulnerability identifier: #VU9651

Vulnerability risk: Low

CVSSv4.0: 5.3 [CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:A/U:Clear]

CVE-ID: CVE-2017-17382

CWE-ID: CWE-310

Exploitation vector: Local network

Exploit availability: Yes

Vulnerable software:
Citrix NetScaler
Server applications / Remote management servers, RDP, SSH

Vendor: Citrix

Description
The vulnerability allows a remote attacker to decrypt TLS traffic. A TLS padding Oracle issue has been detected in Citrix NetScaler Application Delivery Controller (ADC) and NetScaler Gateway. A remote attacker with ability to establish a large number of TLS connections with the target server can conduct a modified version of the Bleichenbacher chosen-ciphertext attack against RSA PKCS#1 v1.5 encryption block formatting and decrypt the data. The attack is known as "ROBOT" (Return Of Bleichenbacher's Oracle Threat).

Mitigation
Install updates from vendor's website:

• Citrix NetScaler ADC and NetScaler Gateway version 12.0 earlier than build 53.22
• Citrix NetScaler ADC and NetScaler Gateway version 11.1 earlier than build 56.19
• Citrix NetScaler ADC and NetScaler Gateway version 11.0 earlier than build 71.22
• Citrix NetScaler ADC and NetScaler Gateway version 10.5 earlier than build 67.13

Vulnerable software versions

Citrix NetScaler: 10.5 Build 50.10 - 12.0 Build 53.13

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External links
https://support.citrix.com/article/CTX230238
https://eprint.iacr.org/2017/1189

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the local network (LAN).

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability. However, a fully functional exploit for this vulnerability is available.