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Vulnerability record · CVE-2020-13998 · published 11 June 2020

CVE-2020-13998: Citrix xenapp observable discrepancy vulnerability

Citrix · Xenapp

Citrix XenApp 6.5, when 2FA is enabled, allows a remote unauthenticated attacker to ascertain whether a user exists on the server, because the 2FA error page only occurs after a valid username is entered. NOTE: This vulnerability only affects products that are no longer supported by the maintainer

5.3 CVSS 3.1 Medium EPSS 1.4% · top 28.8% CWE-203 · Observable discrepancyCWE-639 · Insecure direct object reference
5.3CVSS 3.1 base score, v2 4.3
1.4%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
2References
17 Jun 2026Last modified by NVD

Description

Citrix XenApp 6.5, when 2FA is enabled, allows a remote unauthenticated attacker to ascertain whether a user exists on the server, because the 2FA error page only occurs after a valid username is entered. NOTE: This vulnerability only affects products that are no longer supported by the maintainer

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://gist.github.com/kampji/11e259d68ad98a6f0f898132f1961a96 Third Party Advisory
https://gist.github.com/kampji/11e259d68ad98a6f0f898132f1961a96 Third Party Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.8CVE-2016-6493Citrix xenapp vulnerabilityCitrix XenApp 6.x before 6.5 HRP07 and 7.x before 7.9 and Citrix XenDesktop before 7.9 might allow attackers to weaken an unspecified security mitiga…EPSS 2.2%9.3CVE-2012-5161Citrix xenapp vulnerabilityThe XML Service interface in Citrix XenApp 6.5 and 6.5 Feature Pack 1 allows remote attackers to execute arbitrary code via unspecified vectors.EPSS 5.7%8.8CVE-2020-8283Citrix virtual apps and desktops improper privilege management vulnerabilityAn authorised user on a Windows host running Citrix Universal Print Server can perform arbitrary command execution as SYSTEM in CVAD versions before …EPSS 2.7%8.8CVE-2020-8269Citrix virtual apps and desktops improper privilege management vulnerabilityAn unprivileged Windows user on the VDA can perform arbitrary command execution as SYSTEM in CVAD versions before 2009, 1912 LTSR CU1 hotfixes CTX285…EPSS 2.7%7.8CVE-2021-22928Citrix virtual apps and desktops vulnerabilityA vulnerability has been identified in Citrix Virtual Apps and Desktops that could, if exploited, allow a user of a Windows VDA that has either Citri…EPSS 0.25%7.5CVE-2016-4810Citrix xenapp improper access control vulnerabilityCitrix Studio before 7.6.1000, Citrix XenDesktop 7.x before 7.6 LTSR Cumulative Update 1 (CU1), and Citrix XenApp 7.5 and 7.6 allow attackers to set …EPSS 0.86%7.5CVE-2009-2453Citrix presentation server permissions and access controls vulnerabilityCitrix XenApp (formerly Presentation Server) 4.5 Hotfix Rollup Pack 3 does not apply an access policy when it is defined with the Access Gateway Adva…EPSS 1.4%6.8CVE-2008-4676Citrix access essentials permissions and access controls vulnerabilityUnspecified vulnerability in Citrix XenApp (formerly Presentation Server) 4.5 Feature Pack 1 and earlier, Presentation Server 4.0, and Access Essenti…EPSS 0.29%

Source: NIST National Vulnerability Database (record CVE-2020-13998), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.