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XenappApplication · Citrix

CVE-2020-13998

MEDIUM · 5.3 CVSS v3.1 Published 2020-06-11
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
62/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Citrix XenApp 6.5 with 2FA enabled contains a user enumeration vulnerability where the application returns different responses for valid vs invalid usernames - a 2FA error page appears only after entering a valid username, allowing unauthenticated remote attackers to discover valid user accounts on the server.

MitigationSince XenApp 6.5 is end-of-life and unsupported, migrate to a currently supported version of Citrix Virtual Apps. Alternatively, implement compensating controls such as network-level rate limiting, account lockout policies, or MFA solutions that do not expose user existence through response differences.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
XenappApplication
Affected:= 6.5.0.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
None

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Confirm Citrix XenApp version
    Check the installed version of Citrix XenApp in the system information or by querying the Citrix components. On Windows, this can be found in Add/Remove Programs or the Citrix Installation Manager.
    Affected if The installed version is exactly 6.5.0.0 (other versions are not affected by this specific CVE).
  2. Check if 2FA is enabled
    Review the Citrix XenApp authentication configuration settings. In the Citrix Management Console, navigate to the authentication policies or 2FA/MFA settings for the affected site or farm.
    Affected if Two-factor authentication is enabled - this is the required condition for the vulnerability to exist.
  3. Test user enumeration response differences
    Attempt to authenticate with a known username followed by an invalid or blank 2FA code. Then repeat with a clearly invalid username. Compare the HTTP response pages, error messages, or redirects returned by the server.
    Affected if The response for a valid username differs from the response for an invalid username (e.g., a 2FA prompt appears for valid users while a different error appears for invalid users). This indicates the server is revealing user validity through response differences.
  4. Verify network accessibility
    Confirm the Citrix XenApp Web Interface or Gateway is reachable from untrusted networks on the authentication port (typically port 443 for HTTPS). Check firewall rules and access policies.
    Affected if The login page is exposed to unauthenticated remote attackers without network-level restrictions.

A user is affected if they are running Citrix XenApp 6.5.0.0 with 2FA enabled and the login page returns different responses for valid versus invalid usernames, allowing unauthenticated attackers to enumerate valid accounts.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Since XenApp 6.5 is end-of-life and unsupported, migrate to a currently supported version of Citrix Virtual Apps. Alternatively, implement compensating controls such as network-level rate limiting, account lockout policies, or MFA solutions that do not expose user existence through response differences.

Fix this in Xenapp Scoped from the published advisory
  • Consultation8.0 h
  • Implementation24.0 h
  • Testing8.0 h
  • Review / QA4.0 h
44.0 hours of engineering $7,840
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2020-13998 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
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  • Version or environment caveats, and links to real fixes
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