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Cisco Small Business Switch Security Feature Bypass

High

External Information

Synopsis

Similar to CVE-2018-10933, sending a USER_AUTH_SUCCESS message out of order allows a security feature bypass of certain authentication mechanisms in Cisco Small Business Switches. This could allow an attacker to bypass certificate-based authentication and use password-based authentication -- even if password authentication is disabled.

We tested on a variety of dated Cisco switches and firewalls, each of which had an OpenSSH version of SSH-2.0-OpenSSH_5.9p1.RL or prior. We could not replicate this on any version of mainline OpenSSH or later versions used in Cisco products. This isn't to say that this issue does not exist in other versions, but we were unable to confirm. Cisco was not able to provide us with a list of products -- supported or unsupported.

Solution

See vendor advisory for applicable patch or workaround.

Proof of Concept

https://github.com/tenable/poc/blob/master/cisco/small_business_sf_bypass.py

Disclosure Timeline

Feb 4, 2019 - Vulnerability discovered.
Feb 4, 2019 - Cisco creates internal identifier and supplies Tenable with contact information.
Feb 5, 2019 - Tenable discloses vulnerability details to Cisco.
Feb 5, 2019 - Cisco acknowledges receipt.
Feb 14, 2019 - Tenable requests status update.
Feb 18, 2019 - Cisco requests disclosure timeline.
Feb 20, 2019 - Tenable provides disclosure timeline.
Feb 20, 2019 - Cisco requests clarification.
Feb 21, 2019 - Tenable provides clarification.
March 1, 2019 - Tenable requests status update.
March 1, 2019 - Cisco confirms that the finding is valid, but is unlikely to patch or release an advisory due to the product being out of service.
March 1, 2019 - Tenable requests permission to publish finding ahead of 90 day schedule.
March 2, 2019 - Cisco denies request.
March 7, 2019 - Cisco requests additional clarification.
March 7, 2019 - Tenable provides clarification.
March 27, 2019 - Tenable requests status update.
March 28, 2019 - Cisco states that they've managed to validate the PoC, but have no other updates at this time.
April 4, 2019 - Tenable reminds Cisco of disclosure period expiration (May 5, 2019 marks day 90)
April 4, 2019 - Cisco acknowledges the disclosure deadline.
April 12, 2019 - Cisco requests copy of advisory/write-up draft.
April 12, 2019 - Tenable declines, but notes the information that will be included.
April 24, 2019 - Cisco informs Tenable that an advisory is set to be released on May 1.
May 1, 2019 - Cisco publishes advisory.

All information within TRA advisories is provided “as is”, without warranty of any kind, including the implied warranties of merchantability and fitness for a particular purpose, and with no guarantee of completeness, accuracy, or timeliness. Individuals and organizations are responsible for assessing the impact of any actual or potential security vulnerability.

Tenable takes product security very seriously. If you believe you have found a vulnerability in one of our products, we ask that you please work with us to quickly resolve it in order to protect customers. Tenable believes in responding quickly to such reports, maintaining communication with researchers, and providing a solution in short order.

For more details on submitting vulnerability information, please see our Vulnerability Reporting Guidelines page.

If you have questions or corrections about this advisory, please email [email protected]

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