CVE-2019-13608
Citrix StoreFront Server XML External Entity (XXE) Processing Vulnerability
Description
CVE-2019-13608 is a HIGH-severity XML External Entity (XXE) processing vulnerability in Citrix StoreFront Server, carrying a CVSS 3.1 score of 7.5. The vulnerability allows an unauthenticated attacker to retrieve potentially sensitive information from affected systems through XXE attacks. Affected versions include Citrix StoreFront Server before 1903, 7.15 LTSR before CU4 (3.12.4000), and 7.6 LTSR before CU8 (3.0.8000). 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. The EPSS score of 0.74129 (98.82nd percentile) indicates a very high real-world exploitation probability.
KEV Information
CVSS Score
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:NOpen in CalculatorAffected Products
| Vendor | Product | Version |
|---|---|---|
| citrix | storefront server | >= 1811, < 1903; < 3.12.4000; < 3.0.8000 |
Multiple CVSS Assessments
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
References
- https://support.citrix.com/article/CTX251988(Mitigation, Vendor Advisory)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2019-13608(US Government Resource)
Weakness Type
CWE-611: Improper Restriction of XML External Entity Reference
CVE-2019-13608 is classified under CWE-611 — Improper Restriction of XML External Entity Reference. This weakness occurs when XML input containing a reference to an external entity is processed by a weakly configured XML parser. External entities can reference local files, internal network resources, or remote URLs. When XML parsers process these references without proper restrictions, attackers can read local files including sensitive configuration files and credentials, perform server-side request forgery (SSRF), or cause denial of service.
In the context of Citrix StoreFront Server, the XXE vulnerability allows unauthenticated attackers to craft malicious XML payloads that, when processed by the server, can exfiltrate sensitive data from the file system. StoreFront Server is a critical component of Citrix virtual desktop and application delivery infrastructure, typically deployed in enterprise environments with access to sensitive internal resources. Compromising this component can provide attackers with credentials, configuration data, and a foothold for further lateral movement.
Learn more: CWE-611 — Improper Restriction of XML External Entity Reference
Impact Analysis
CVE-2019-13608 carries a CVSS 3.1 score of 7.5 (HIGH) with Unchanged Scope.
Confidentiality (HIGH): Successful exploitation through XXE allows attackers to read arbitrary files from the server, including configuration files, credentials, certificates, and other sensitive data stored on the StoreFront Server. This can expose internal network details and authentication tokens.
Integrity (NONE): The vulnerability does not allow direct modification of data on the affected system.
Availability (NONE): While XXE attacks can theoretically cause denial of service through recursive entity expansion (Billion Laughs attack), the primary impact of this vulnerability is information disclosure.
Scope Unchanged: The exploitation is contained within the StoreFront Server component, though exposed information may enable attacks against other systems in the Citrix infrastructure.
With an EPSS score of 0.74129 (98.82nd percentile) and confirmed ransomware association, this vulnerability represents a critical risk requiring urgent attention.
Exploit Maturity
CVE-2019-13608 has confirmed active exploitation in the wild and is listed in CISA's Known Exploited Vulnerabilities catalog.
Exploit status: The vulnerability has been actively exploited, as confirmed by its KEV listing. The EPSS score of 0.74129 (98.82nd percentile) places it among the most exploited vulnerabilities tracked. XXE attacks are well-understood and exploitation tools are widely available.
Ransomware association: CVE-2019-13608 has a confirmed association with ransomware campaigns. This makes the vulnerability especially critical, as threat actors have integrated it into ransomware kill chains targeting enterprise Citrix environments. Organizations should treat this as a top-priority remediation item.
Attack surface: Citrix StoreFront Server is typically accessible from corporate networks and sometimes from the internet as part of Citrix virtual desktop infrastructure. The unauthenticated nature of the attack significantly increases its risk. Enterprise Citrix deployments are high-value targets for ransomware operators.
KEV deadline: CISA required federal agencies to remediate this vulnerability by 2022-05-03. Given the ransomware association, all organizations should treat remediation as an emergency priority.
Remediation
- Apply vendor patches immediately. Update to Citrix StoreFront Server 1903 or later, 7.15 LTSR CU4 (3.12.4000) or later, or 7.6 LTSR CU8 (3.0.8000) or later. Consult Citrix support article CTX251988 for detailed guidance.
- Verify all StoreFront Server instances. Identify every StoreFront Server deployment in your environment and confirm their software versions. Use your asset management tools to ensure no instances are missed.
- Restrict network access. Limit access to the StoreFront Server to authorized clients only. Implement network segmentation to isolate StoreFront from sensitive internal resources.
- Scan for indicators of compromise. Given the ransomware association, conduct thorough investigation for signs of compromise. Look for unusual file access patterns, unexpected outbound connections, or data exfiltration attempts. Check for ransomware precursor activities.
- Harden XML processing. As a defense-in-depth measure, configure XML parsers to disable external entity processing and DTD processing. This protects against similar XXE attacks in the future.
- Review and rotate credentials. Assume that credentials stored on or accessible from the StoreFront Server may have been compromised. Rotate service account passwords, API keys, and certificates that the server can access.
Technical Details
CVE-2019-13608 is a HIGH-severity XXE vulnerability exploitable over the network with low attack complexity. No authentication or user interaction is required.
Technical mechanism: Citrix StoreFront Server processes XML input without properly restricting external entity references. An attacker can submit crafted XML payloads containing external entity declarations that reference local files (using file:// protocol) or internal network resources (using http:// protocol). When the XML parser processes these entities, it fetches the referenced content and includes it in the response, allowing the attacker to exfiltrate sensitive data.
CVSS 3.1 vector analysis (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N): The network-based attack vector with no authentication required and no user interaction makes this vulnerability highly accessible. The HIGH confidentiality impact reflects the ability to read arbitrary files, while integrity and availability are unaffected.
Affected versions: Citrix StoreFront Server before 1903 (current release branch), 7.15 LTSR before CU4 (3.12.4000), and 7.6 LTSR before CU8 (3.0.8000). These versions span multiple Long Term Service Release branches commonly deployed in enterprise environments.
Frequently Asked Questions
Is CVE-2019-13608 being actively exploited?
Yes, CVE-2019-13608 is actively exploited in the wild and has a confirmed association with ransomware campaigns. The EPSS score of 0.74129 (98.82nd percentile) confirms very high real-world exploitation activity. This makes it a top-priority vulnerability for remediation.
What products are affected by CVE-2019-13608?
Citrix StoreFront Server versions before 1903, 7.15 LTSR before CU4 (3.12.4000), and 7.6 LTSR before CU8 (3.0.8000) are affected. StoreFront Server is a key component of Citrix virtual desktop and application delivery infrastructure.
How do I fix CVE-2019-13608?
Update to the latest patched version: StoreFront Server 1903 or later, 7.15 LTSR CU4 or later, or 7.6 LTSR CU8 or later. Consult Citrix support article CTX251988 for specific guidance. Additionally, restrict network access and harden XML processing configurations.
How severe is CVE-2019-13608?
CVE-2019-13608 is rated HIGH with a CVSS 3.1 score of 7.5. The vulnerability is particularly dangerous due to its confirmed ransomware association and the critical role StoreFront Server plays in enterprise Citrix deployments. Exploitation requires no authentication and allows reading sensitive files from the server.
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