CVE-2019-11634
Citrix Workspace Application and Receiver for Windows Remote Code Execution Vulnerability
Description
CVE-2019-11634 is a CRITICAL remote code execution vulnerability affecting Citrix Workspace Application and Receiver for Windows, carrying a CVSS 3.1 score of 9.8. The vulnerability results from local drive access preferences not being properly enforced in the client application, allowing attackers to gain unauthorized access to the client's local drives and potentially execute arbitrary code. Affected products include Citrix Receiver for Windows (version 4.9) and Citrix Workspace for Windows (versions before 1904). This CVE is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog with a remediation deadline of 2022-05-03 and is confirmed to be associated with ransomware campaigns. With an EPSS score of 0.31160 (96.68th percentile), this vulnerability demonstrates substantial exploitation activity.
KEV Information
CVSS Score
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HOpen in CalculatorAffected Products
| Vendor | Product | Version |
|---|---|---|
| citrix | receiver | 4.9 |
| citrix | workspace | < 1904 |
Multiple CVSS Assessments
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
References
- https://support.citrix.com/article/CTX251986(Vendor Advisory)
- https://support.citrix.com/v1/search?searchQuery=%22%22&lang=en&sort=cr_date_desc&prod=&pver=&ct=Security+Bulletin(Vendor Advisory)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2019-11634(US Government Resource)
Weakness Type
CWE-284: Improper Access Control
CVE-2019-11634 is classified under CWE-284 — Improper Access Control. This weakness occurs when a product does not properly restrict access to resources, allowing unauthorized actors to interact with system components beyond their intended privilege level. Access control failures can manifest in various forms including broken authentication, insufficient authorization checks, missing permission validations, and failure to enforce configured security policies.
In the context of Citrix Workspace Application and Receiver for Windows, the improper access control manifests as a failure to enforce local drive access preferences configured by administrators. This means that even when drive mapping restrictions are configured, attackers can bypass these controls to access the client machine's local file system. Since Citrix Workspace and Receiver are widely deployed in enterprise environments for remote desktop and virtual application access, this vulnerability provides a direct pathway from the Citrix session to the local workstation, enabling file theft, malware deployment, and lateral movement.
Learn more: CWE-284 — Improper Access Control
Impact Analysis
CVE-2019-11634 carries a CVSS 3.1 score of 9.8 (CRITICAL) with Unchanged Scope.
Confidentiality (HIGH): Successful exploitation grants the attacker full access to the client workstation's local drives, enabling theft of sensitive documents, credentials, certificates, and any other locally stored data. In enterprise environments, this can expose corporate intellectual property and personal user data.
Integrity (HIGH): Attackers can write arbitrary files to the client's local drives, enabling deployment of malware, backdoors, ransomware payloads, and modification of system files or application configurations on the endpoint.
Availability (HIGH): Complete disruption of the client workstation is possible through destructive file operations, ransomware deployment, or system corruption via the unauthorized drive access.
Scope Unchanged: The vulnerability's scope is technically Unchanged within the CVSS framework, though the practical impact bridges the gap between the Citrix virtual session and the local workstation environment.
With an EPSS score of 0.31160 (96.68th percentile), this vulnerability ranks among the most likely to be exploited in real-world attacks.
Exploit Maturity
CVE-2019-11634 has confirmed active exploitation in the wild and is listed in CISA's Known Exploited Vulnerabilities catalog with confirmed ransomware association.
Exploit status: This vulnerability has been actively exploited as confirmed by its KEV listing and ransomware association. The EPSS score of 0.31160 (96.68th percentile) places it among the most likely vulnerabilities to be exploited.
Ransomware association: CVE-2019-11634 is confirmed to be associated with ransomware campaigns. The vulnerability's ability to provide unauthorized access to local drives makes it an effective vector for ransomware deployment on endpoint systems connected through Citrix environments.
Attack surface: The vulnerability affects Citrix Workspace and Receiver clients installed on Windows endpoints across enterprise environments. Given the widespread deployment of these applications for remote work and virtual desktop infrastructure, the attack surface is extensive. Exploitation requires network access but no authentication or user interaction.
KEV deadline: CISA required federal agencies to remediate this vulnerability by 2022-05-03. All organizations should treat this deadline as a strong recommendation for their own remediation timelines.
Remediation
- Update Citrix Workspace Application immediately. Upgrade Citrix Workspace for Windows to version 1904 or later. For Citrix Receiver, upgrade to a supported version as recommended by Citrix advisory CTX251986. This vulnerability demands priority patching due to its ransomware association.
- Inventory all Citrix client installations. Identify every Windows endpoint running Citrix Workspace or Receiver. Use endpoint management tools and software inventory systems to ensure no installations are missed, including versions on remote worker laptops.
- Enforce drive mapping restrictions. Review and enforce Citrix drive mapping policies through Citrix StoreFront and Group Policy configurations. Verify that local drive access is limited to the minimum required for business operations.
- Scan for indicators of compromise. Review endpoint detection logs for unauthorized file access patterns, unexpected executables written to local drives, and anomalous Citrix client behavior. Investigate any suspicious activity discovered during the audit.
- Implement application whitelisting on endpoints. Deploy application control solutions that prevent unauthorized executables from running, even if an attacker manages to write files to local drives through this vulnerability.
- Conduct a post-remediation review. After updating all clients, verify the fix by confirming that drive mapping restrictions are properly enforced. Document all remediation actions and update vulnerability management records.
Technical Details
CVE-2019-11634 is a CRITICAL-severity vulnerability in Citrix Workspace Application and Receiver for Windows that can be exploited remotely over the network. The attack complexity is low, requiring no specialized conditions. No prior authentication or privileges are needed, and no user interaction is required.
Technical mechanism: The vulnerability stems from incorrect access control in the Citrix Workspace Application and Receiver for Windows. Specifically, the client software fails to properly enforce configured local drive access preferences. When administrators configure drive mapping restrictions to prevent Citrix sessions from accessing local drives, the enforcement mechanism can be bypassed. This allows an attacker who controls or compromises the Citrix session to read from and write to the local drives of the Windows endpoint running the vulnerable client.
Affected products and versions: Citrix Receiver for Windows version 4.9 and Citrix Workspace for Windows versions before 1904.
CVSS 3.1 vector analysis: The vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H reflects that exploitation is possible over the network with low complexity, no privileges, and no user interaction, with maximum impact to confidentiality, integrity, and availability. The critical rating reflects the severity of unauthorized local drive access in enterprise Citrix deployments.
Frequently Asked Questions
Is CVE-2019-11634 being actively exploited?
Yes, CVE-2019-11634 is actively exploited and is listed in CISA's KEV catalog with confirmed ransomware association. The EPSS score of 0.31160 (96.68th percentile) confirms a high exploitation probability. Attackers leverage this vulnerability to bypass Citrix drive mapping restrictions and access local endpoint file systems.
What products are affected by CVE-2019-11634?
CVE-2019-11634 affects Citrix Receiver for Windows version 4.9 and Citrix Workspace for Windows versions prior to 1904. Organizations should check all Windows endpoints running these Citrix client applications. Consult the Citrix advisory CTX251986 for the complete list of affected and fixed versions.
How do I fix CVE-2019-11634?
Upgrade Citrix Workspace for Windows to version 1904 or later. For Citrix Receiver, upgrade to a supported version per Citrix advisory CTX251986. After updating, verify that local drive access restrictions are properly enforced. Use endpoint management tools to ensure no unpatched installations remain in your environment.
How severe is CVE-2019-11634?
CVE-2019-11634 is rated CRITICAL with a CVSS 3.1 score of 9.8. The vulnerability enables unauthorized access to local drives on Windows endpoints running Citrix client software, providing a direct pathway for data theft and ransomware deployment. Its KEV listing and confirmed ransomware association underscore the urgency of remediation.
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