PoC Exploits Released for Citrix ADC and Gateway RCE Vulnerability

Jan 11, 2020

It’s now or never to prevent your enterprise servers running
vulnerable versions of Citrix application delivery, load balancing,
and Gateway solutions from getting hacked by remote attackers.

Why the urgency? Earlier today, multiple groups publicly
released weaponized proof-of-concept exploit code [1, 2] for a recently disclosed remote code execution
vulnerability in Citrix’s NetScaler ADC and Gateway products that
could allow anyone to leverage them to take full control over
potential enterprise targets.

Just before the last Christmas and year-end holidays, Citrix
announced that its
Citrix Application Delivery Controller (ADC) and Citrix Gateway are
vulnerable to a critical path traversal flaw (CVE-2019-19781) that
could allow an unauthenticated attacker to perform arbitrary code
execution on vulnerable servers.
^[1]

Citrix confirmed that the flaw affects all supported version of the
software, including:

Citrix ADC and Citrix Gateway version 13.0 all supported
builds
Citrix ADC and NetScaler Gateway version 12.1 all supported
builds
Citrix ADC and NetScaler Gateway version 12.0 all supported
builds
Citrix ADC and NetScaler Gateway version 11.1 all supported
builds
Citrix NetScaler ADC and NetScaler Gateway version 10.5 all
supported builds

The company made the disclose without releasing any security
patches for vulnerable software; instead, Citrix offered
mitigation to help administrators guard their servers against
potential remote attacks⁠—and even at the time of writing, there’s
no patch available almost 23 days after disclosure.
Through the cyberattacks against vulnerable servers were first seen in the
wild last week when hackers developed private exploit after
reverse engineering mitigation information, the public release of
weaponized PoC would now make it easier for low-skilled script
kiddies to launch cyberattacks against vulnerable
organizations.
According to Shodan, at the
time of writing, there are over 125,400 Citrix ADC or Gateway
servers publicly accessible and can be exploited overnight if not
taken offline or protected using available mitigation.

While discussing technical
details ^[5] of the flaw in a blog
post published yesterday, MDSsec also released a video
demonstration of the exploit they developed but chose not to
release it at this moment.

Besides applying the recommended mitigation, Citrix ADC
administrators are also advised to monitor their device logs for
attacks.

^[2]^[3]^[4]

References

^{^}
announced
(support.citrix.com)
^{^}
Citrix offered mitigation
(support.citrix.com)
^{^}
first seen in the wild
(twitter.com)
^{^}
Shodan
(beta.shodan.io)
^{^}
technical details
(www.mdsec.co.uk)

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OWASP TOP !0

Injection. Injection flaws, such as SQL, NoSQL, OS, and LDAP injection, occur when untrusted data is sent to an interpreter as part of a command or query. The attacker’s hostile data can trick the interpreter into executing unintended commands or accessing data without proper authorization. Broken Authentication. Application functions related to authentication and session management are often implemented incorrectly, allowing attackers to compromise passwords, keys, or session tokens, or to exploit other implementation flaws to assume other users’ identities temporarily or permanently. Sensitive Data Exposure. Many web applications and APIs do not properly protect sensitive data, such as financial, healthcare, and PII. Attackers may steal or modify such weakly protected data to conduct credit card fraud, identity theft, or other crimes. Sensitive data may be compromised without extra protection, such as encryption at rest or in transit, and requires special precautions when exchanged with the browser. XML External Entities (XXE). Many older or poorly configured XML processors evaluate external entity references within XML documents. External entities can be used to disclose internal files using the file URI handler, internal file shares, internal port scanning, remote code execution, and denial of service attacks. Broken Access Control. Restrictions on what authenticated users are allowed to do are often not properly enforced. Attackers can exploit these flaws to access unauthorized functionality and/or data, such as access other users’ accounts, view sensitive files, modify other users’ data, change access rights, etc. Security Misconfiguration. Security misconfiguration is the most commonly seen issue. This is commonly a result of insecure default configurations, incomplete or ad hoc configurations, open cloud storage, misconfigured HTTP headers, and verbose error messages containing sensitive information. Not only must all operating systems, frameworks, libraries, and applications be securely configured, but they must be patched/upgraded in a timely fashion. Cross-Site Scripting XSS. XSS flaws occur whenever an application includes untrusted data in a new web page without proper validation or escaping, or updates an existing web page with user-supplied data using a browser API that can create HTML or JavaScript. XSS allows attackers to execute scripts in the victim’s browser which can hijack user sessions, deface web sites, or redirect the user to malicious sites. Insecure Deserialization. Insecure deserialization often leads to remote code execution. Even if deserialization flaws do not result in remote code execution, they can be used to perform attacks, including replay attacks, injection attacks, and privilege escalation attacks. Using Components with Known Vulnerabilities. Components, such as libraries, frameworks, and other software modules, run with the same privileges as the application. If a vulnerable component is exploited, such an attack can facilitate serious data loss or server takeover. Applications and APIs using components with known vulnerabilities may undermine application defenses and enable various attacks and impacts. Insufficient Logging & Monitoring. Insufficient logging and monitoring, coupled with missing or ineffective integration with incident response, allows attackers to further attack systems, maintain persistence, pivot to more systems, and tamper, extract, or destroy data. Most breach studies show time to detect a breach is over 200 days, typically detected by external parties rather than internal processes or monitoring.

PoC Exploits Released for Citrix ADC and Gateway RCE Vulnerability

References

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