CVE-2021-20875
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 · uneditedOpen redirect vulnerability in GroupSession Free edition ver5.1.1 and earlier, GroupSession byCloud ver5.1.1 and earlier, and GroupSession ZION ver5.1.1 and earlier allows a remote unauthenticated attacker to redirect users to arbitrary web sites and conduct phishing attacks by having a user to access a specially crafted URL.
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 · moderate confidenceOpen redirect vulnerability in GroupSession versions 5.1.1 and earlier across Free, byCloud, and ZION editions. An unauthenticated remote attacker can craft a malicious URL containing a manipulated parameter that causes the application to redirect users to an attacker-controlled arbitrary website, facilitating phishing attacks.
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<= 5.1.1CVSS 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 checksWork through these to decide whether this CVE applies to you.
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Identify GroupSession installationLocate the GroupSession application server (typically Apache Tomcat) and identify if GroupSession software is deployed. Check for groupsession.war or the groupsession directory in the webapps folder.Affected if GroupSession is installed on the system
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Determine installed GroupSession versionAccess the GroupSession login page and locate the version information, typically found in the footer or under 'System Information' in the admin panel. Alternatively, check the WAR file or deployment descriptor for the version metadata.Affected if The installed version is 5.1.1 or earlier (any version <= 5.1.1)
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Identify if redirect parameters are accessibleTest for the presence of redirect-handling parameters by observing URL parameters during normal GroupSession usage (such as after logout or when clicking links that trigger redirects). Review web server access logs for requests containing redirect-related parameter names.Affected if Redirect parameters are present in the application and accessible without authentication
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Verify redirect parameter validation is absent or weakTest the redirect functionality by crafting a URL with a suspected redirect parameter pointing to an external domain (for example, adding '?redirect=http://example.com' to a GroupSession URL). Observe whether the application allows the redirect to an arbitrary external URL without validation.Affected if The application redirects to arbitrary external URLs without validating that the destination is a trusted internal resource
A user is affected if GroupSession version 5.1.1 or earlier is installed AND unauthenticated external redirect via URL parameters is possible without validation.
Generated from the published advisory. Verify against your own configuration.
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 dataApply the vendor patch (upgrade to version 5.1.2 or later) and implement strict validation of redirect parameters to ensure only trusted destinations are allowed.
- Consultation2.0 h
- Implementation4.0 h
- Testing2.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,848.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-20875 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-20875 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- 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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