CVE-2016-4028
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 · uneditedAn issue was discovered in Open-Xchange OX Guard before 2.4.0-rev8. OX Guard uses an authentication token to identify and transfer guest users' credentials. The OX Guard API acts as a padding oracle by responding with different error codes depending on whether the provided token matches the encryption padding. In combination with AES-CBC, this allows attackers to guess the correct padding. Attackers may run brute-forcing attacks on the content of the guest authentication token and discover user credentials. For a practical attack vector, the guest users needs to have logged in, the content of the guest user's "OxReaderID" cookie and the value of the "auth" parameter needs to be known to the attacker.
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 confidenceThe OX Guard API acts as a padding oracle by returning different error codes depending on whether the decryption padding is valid. Combined with AES-CBC mode, this allows attackers to iteratively guess bytes of the guest authentication token, eventually decrypting it to discover user credentials.
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<= 2.4.0CVSS 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
- High
- Privileges
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.0/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
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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Locate OX Guard installation directoryCheck the file system for OX Guard installation paths, typically found in /opt/open-xchange-guard, /usr/local/oxguard, or the application's lib directory. Look for guard.jar or similar OX Guard binaries.Affected if OX Guard binaries are present on the system
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Determine installed OX Guard versionInspect the version information embedded in the OX Guard JAR file (e.g., guard.jar MANIFEST.MF), or run the command 'rpm -q open-xchange-guard' or 'dpkg -l open-xchange-guard' if installed via package manager. Check any version file in the installation directory.Affected if The installed version is 2.4.0 or any earlier version
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Verify API endpoint exposureCheck network configuration and firewall rules to determine if the OX Guard API ports (typically 8111 or configured HTTPS port) are accessible from untrusted networks. Review server.xml or similar configuration files for exposed binding addresses.Affected if The OX Guard API is reachable from network locations outside the trusted perimeter
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Confirm AES-CBC encryption configurationReview OX Guard configuration files (guard.properties, config.xml, or similar) to identify if AES-CBC mode is configured for encryption operations, particularly for token handling.Affected if AES-CBC mode is enabled in the encryption configuration
The environment is affected if OX Guard version 2.4.0 or earlier is installed and the API is accessible, since the padding oracle vulnerability requires the vulnerable version to be exposed.
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 dataUpgrade to OX Guard 2.4.0-rev8 or later, which fixes the padding oracle by ensuring consistent error responses regardless of padding validity.
- Consultation2.0 h
- Implementation4.0 h
- Testing6.0 h
- Review / QA3.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2016-4028 — 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-2016-4028 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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