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Access GatewayApplication · Citrix

CVE-2011-2883

HIGH · 9.3 CVSS v2.0 Published 2011-07-21
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
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
The NSEPA.NsepaCtrl.1 ActiveX control in nsepa.ocx in Citrix Access Gateway Enterprise Edition 8.1 before 8.1-67.7, 9.0 before 9.0-70.5, and 9.1 before 9.1-96.4 attempts to validate signed DLLs by checking the certificate subject, not the signature, which allows man-in-the-middle attackers to execute arbitrary code via HTTP header data referencing a DLL that was signed with a crafted certificate.

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

The NSEPA.NsepaCtrl.1 ActiveX control (nsepa.ocx) in Citrix Access Gateway Enterprise Edition validates signed DLLs by only checking the certificate subject name rather than verifying the cryptographic signature, allowing man-in-the-middle attackers to inject malicious DLLs signed with crafted certificates and achieve arbitrary code execution.

MitigationUpgrade Citrix Access Gateway to version 8.1-67.7, 9.0-70.5, or 9.1-96.4 or later to implement proper signature validation; alternatively, disable the ActiveX control in Internet Explorer security settings or block it via group policy.

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
Access GatewayApplication
Affected:= 8.1= 9.0= 9.1

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
M
Authentication
None
Confidentiality
Complete
Integrity
Complete
Availability
Complete

AV:N/AC:M/Au:N/C:C/I:C/A:C

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. Identify Citrix Access Gateway installation and version
    On the Citrix Access Gateway server, check the installed version via the system control panel, Citrix installation logs, or by running ' Citrix Access Gateway - version' from the command line. If accessing remotely, query the system inventory or contact the administrator for the installed version number.
    Affected if The installed version is 8.1, 9.0, or 9.1 (exact match to the affected versions listed)
  2. Locate the nsepa.ocx ActiveX control file
    Search for nsepa.ocx on the system. Common paths include the Windows system directory (C:\Windows\System32\) or the Citrix installation directory (C:\Program Files\Citrix\). Use the command 'dir /s nsepa.ocx' or File Explorer search.
    Affected if The file nsepa.ocx exists on the system, indicating the ActiveX control is present
  3. Check if NSEPA.NsepaCtrl.1 ActiveX control is registered
    Open Windows Registry and navigate to HKEY_CLASSES_ROOT\NSEPA.NsepaCtrl.1, or run 'regsvr32 /s nsepa.ocx' to attempt registration and observe the result. The ActiveX control must be registered for it to be loadable in Internet Explorer.
    Affected if The registry key HKEY_CLASSES_ROOT\NSEPA.NsepaCtrl.1 exists, meaning the control is registered and potentially loadable by IE
  4. Verify the ActiveX control is enabled in Internet Explorer
    Open Internet Explorer, go to Tools > Internet Options > Security > Custom Level, and inspect the settings under 'ActiveX controls and plugins'. Alternatively, check the Windows Group Policy settings under Computer Configuration > Administrative Templates > Windows Components > Internet Explorer > Security Features > Add-on Management.
    Affected if The ActiveX control is allowed to run (set to Enable or Prompt) in IE security zones, particularly the Trusted or Intranet zones where the Citrix portal would be accessed

A system is affected if it runs Citrix Access Gateway version 8.1, 9.0, or 9.1 with the nsepa.ocx ActiveX control present, registered, and enabled in Internet Explorer.

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.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade Citrix Access Gateway to version 8.1-67.7, 9.0-70.5, or 9.1-96.4 or later to implement proper signature validation; alternatively, disable the ActiveX control in Internet Explorer security settings or block it via group policy.

Recommended fix High confidence

Citrix Access Gateway Enterprise Edition 8.1-67.7 or later; 9.0-70.5 or later; 9.1-96.4 or later

  1. 1. Identify the currently installed Citrix Access Gateway version (8.1, 9.0, or 9.1)
  2. 2. For version 8.1: Upgrade to version 8.1-67.7 or later
  3. 3. For version 9.0: Upgrade to version 9.0-70.5 or later
  4. 4. For version 9.1: Upgrade to version 9.1-96.4 or later
  5. 5. Obtain the appropriate upgrade package from Citrix official support channels
  6. 6. Follow Citrix standard upgrade procedures for Access Gateway Enterprise Edition
  7. 7. After upgrade, verify the NSEPA.NsepaCtrl.1 ActiveX control (nsepa.ocx) has been updated
  8. 8. Test that the certificate validation now properly verifies signatures rather than just certificate subjects
Caveat Review Citrix release notes for upgrade considerations between minor versions; ensure compatibility with existing backend systems

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Access Gateway Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,750
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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-2011-2883 in production — separate from our analysis above.

No notes yet

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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
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data