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CableTap/doc/advisories/bastille-28.session-cookie-write.txt
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| Bastille Tracking Number 28 | |
| CVE-2017-9485 | |
| Overview | |
| A vulnerability has been discovered that enables an attacker to write arbitrary data to a session cookie stored at a known location on a target gateway. | |
| Affected Platforms | |
| Cisco DPC3939, firmware version dpc3939-P20-18-v303r20421746-170221a-CMCST | |
| Proof-of-Concept | |
| Using the syseventd vulnerability (Bastille Tracking Number 22), an attacker can put a target gateway into UI dev mode by creating the file /var/ui_dev_mode on disk. | |
| When this file is present on the gateway, the web UI bypasses the normal authentication logic, and accepts any password, as long as a valid username is entered. | |
| As a result of bypassing the normal authentication logic, when an invalid username is entered, session data is written to disk, but never deleted. | |
| An attacker can therefore enter arbitrary data into the username field, which gets written to disk at the following path: | |
| /var/tmp/sess_[PHP Session ID] | |
| The PHP Session ID is included in the login attempt HTTP response, giving the attacker control of the contents of a file at a known location on the gateway. | |
| Test Environment | |
| Cisco DPC3939, firmware version dpc3939-P20-18-v303r20421746-170221a-CMCST | |
| Mitigation | |
| There is no apparent mechanism to allow Comcast customers to control or change this behavior. | |
| Recommended Remediation | |
| Modify the web UI to delete the session data when a user enters an invalid username. | |
| Credits | |
| Marc Newlin and Logan Lamb, Bastille | |
| Chris Grayson, Web Sight.IO |