{"cve":"CVE-2016-4028","nvd":{"published":"2016-12-15T06:59:07.457","modified":"2026-06-17T00:46:45.600","status":"Modified","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.","cvss_v4":null,"cvss_v3":{"version":"3.0","vector":"CVSS:3.0/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H","score":7.5},"cwes":["CWE-255"],"references":["http://www.securityfocus.com/archive/1/538732/100/0/threaded","http://www.securitytracker.com/id/1036154","http://www.securityfocus.com/archive/1/538732/100/0/threaded","http://www.securitytracker.com/id/1036154"],"products":["open-xchange:ox_guard"],"source":"nvd","synced_at":"2026-10-19T20:41:25.729257544+00:00"},"epss":{"cve":"CVE-2016-4028","score":0.00709,"percentile":0.53501,"date":"2026-10-31"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}