CVE-2016-4028: An 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' creden...

Description

An 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.

Metrics

EPSS Probability

0.71%

48.7th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-255

Affected Software

Vendor	Product	Versions	Update
Open-Xchange	Ox Guard	<= 2.4.0	Rev7

References

http://www.securityfocus.com/archive/1/538732/100/0/threaded
http://www.securitytracker.com/id/1036154Third Party Advisory, VDB Entry
http://www.securityfocus.com/archive/1/538732/100/0/threaded
http://www.securitytracker.com/id/1036154Third Party Advisory, VDB Entry

Timeline

Published: Dec 15, 2016
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2016-4028?

An 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.

How severe is CVE-2016-4028?

Severity scoring for CVE-2016-4028 is pending analysis. The EPSS model estimates a 0.71% probability of exploitation in the next 30 days.

How do I fix CVE-2016-4028?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.