CVE-2021-21491Network attack vector

User redirection via retained opener context

Published Mar 10, 2021 · Updated Aug 3, 2024

Reverse tabnabbing in WebDynPro Java in SAP NetWeaver Application Server Java 7.00 through 7.50 allows attackers to redirect users. Links that open a new tab retain an opener reference, allowing the destination to assign window.opener.location and replace the original page with a phishing site. Exploitation requires a user to activate an affected outbound link; the result is browser-page redirection rather than direct modification of server data.

CVSS severity6.1
Medium
EPSS probability0.67%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Reverse tabnabbing in WebDynPro Java in SAP NetWeaver Application Server Java 7.00 through 7.50 allows attackers to redirect users. Links that open a new tab retain an opener reference, allowing the destination to assign window.opener.location and replace the original page with a phishing site. Exploitation requires a user to activate an affected outbound link; the result is browser-page redirection rather than direct modification of server data.

The record

CVE
CVE-2021-21491
Published
Mar 10, 2021
Updated
Aug 3, 2024
Vendor
SAP SE
Product
SAP NetWeaver Application Server Java
Classifications
CWE-601, T1566.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 10, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 7.00
  2. Affected versionversion=< 7.10
  3. Affected versionversion=< 7.11
  4. Affected versionversion=< 7.20
  5. Affected versionversion=< 7.30
  6. Affected versionversion=< 731
  7. Affected versionversion=< 7.40
  8. Affected versionversion=< 7.50

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

SAP SE · SAP NetWeaver Application Server Javaversion=< 7.00; version=< 7.10; version=< 7.11; version=< 7.20; version=< 7.30; version=< 731; version=< 7.40; version=< 7.50

Published CVSS scores

5.8NVDAV:N/AC:M/Au:N/C:P/I:P/A:N
6.1NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-601URL Redirection to Untrusted Site ('Open Redirect')
T1566.002Spearphishing Link

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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