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Netweaver Application Server JavaApplication · Sap

CVE-2021-21491

MEDIUM · 6.1 CVSS v3.1 Published 2021-03-10
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
68/100
Remediation priority · Elevated
Remotely reachable No privileges

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
SAP Netweaver Application Server Java (Applications based on WebDynpro Java) versions 7.00, 7.10, 7.11, 7.20, 7.30, 7.31, 7.40, 7.50, allow an attacker to redirect users to a malicious site due to Reverse Tabnabbing vulnerabilities.

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

This is a Reverse Tabnabbing vulnerability in SAP NetWeaver AS Java WebDynpro Java components. Attackers can craft malicious links that, when clicked by users, allow the opened page to manipulate the original tab's location via the window.opener object, redirecting users to attacker-controlled phishing sites.

MitigationApply rel='noopener noreferrer' attribute to all external links generated by WebDynpro components, or use JavaScript window.opener = null when opening new windows to prevent the opened page from accessing the referrer's window object.

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
Netweaver Application Server JavaApplication
Affected:= 7.00= 7.10= 7.11= 7.20= 7.30= 7.31= 7.40= 7.50

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
Required
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/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. Identify SAP NetWeaver AS Java installation and version
    Check the SAP system for the NetWeaver AS Java version by inspecting the SAP Manage Engine, looking at the system info in SAP Central ProcMgmt, or querying the SAP Java engine via SAP MMC or SAP NetWeaver Administrator. Common paths: /usr/sap/<SID>/SC01/j2ee/ or check SAP NW version via SAP LM or NWA.
    Affected if The installed version matches 7.00, 7.10, 7.11, 7.20, 7.30, 7.31, 7.40, or 7.50 exactly (these are the only affected versions listed).
  2. Confirm WebDynpro Java components are deployed
    Review deployed WebDynpro applications in the SAP NetWeaver Administrator (NWA) under Application Management > Applications, or inspect the file system under /usr/sap/<SID>/<instance>/j2ee/cluster/apps/ for WebDynpro application archives (.sda or .war files containing WebDynpro content).
    Affected if WebDynpro Java components are deployed and active on the system.
  3. Identify external links generated by WebDynpro applications
    Search WebDynpro source code (WD Java classes) or deployed application files for HTML anchor tags (a href=) that link to external domains. Usegrep or similar tools on the application's source directories to find link generation patterns.
    Affected if WebDynpro applications generate anchor tags linking to external URLs.
  4. Inspect link attributes for missing protection
    Examine each external anchor tag for the presence of rel='noopener noreferrer' or rel='noopener' attributes. Also check for JavaScript window.opener = null patterns in any window.open() calls. Review the generated HTML output or the code that builds these links.
    Affected if External links lack rel='noopener noreferrer' or rel='noopener' attributes, AND window.opener nullification is not implemented, meaning the opened page can access window.opener.

You are affected if you run SAP NetWeaver AS Java versions 7.00-7.50 with WebDynpro Java components deployed, and those components generate external links without rel='noopener noreferrer' or equivalent window.opener protection.

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

Apply rel='noopener noreferrer' attribute to all external links generated by WebDynpro components, or use JavaScript window.opener = null when opening new windows to prevent the opened page from accessing the referrer's window object.

Fix this in Netweaver Application Server Java Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing3.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,490
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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-2021-21491 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
  • 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
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