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             AUSCERT External Security Bulletin Redistribution

     ConfD CLI Secure Shell Server Privilege Escalation Vulnerability
                               5 August 2021


        AusCERT Security Bulletin Summary

Product:           Cisco ConfD
Publisher:         Cisco Systems
Operating System:  Cisco
Impact/Access:     Execute Arbitrary Code/Commands -- Existing Account
                   Increased Privileges            -- Existing Account
Resolution:        Patch/Upgrade
CVE Names:         CVE-2021-1572  

Original Bulletin: 

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ConfD CLI Secure Shell Server Privilege Escalation Vulnerability

Priority:        High
Advisory ID:     cisco-sa-confd-priv-esc-LsGtCRx4
First Published: 2021 August 4 16:00 GMT
Version 1.0:     Final
Workarounds:     No workarounds available
Cisco Bug IDs:   CSCvy43896
CVE Names:       CVE-2021-1572
CWEs:            CWE-266


  o A vulnerability in ConfD could allow an authenticated, local attacker to
    execute arbitrary commands at the level of the account under which ConfD is
    running, which is commonly root . To exploit this vulnerability, an
    attacker must have a valid account on an affected device.

    The vulnerability exists because the affected software incorrectly runs the
    SFTP user service at the privilege level of the account that was running
    when the ConfD built-in Secure Shell (SSH) server for CLI was enabled. If
    the ConfD built-in SSH server was not enabled, the device is not affected
    by this vulnerability. An attacker with low-level privileges could exploit
    this vulnerability by authenticating to an affected device and issuing a
    series of commands at the SFTP interface. A successful exploit could allow
    the attacker to elevate privileges to the level of the account under which
    ConfD is running, which is commonly root .

    Note: Any user who can authenticate to the built-in SSH server may exploit
    this vulnerability. By default, all ConfD users have this access if the
    server is enabled.

    Software updates that address this vulnerability have been released. There
    are no workarounds that address this vulnerability.

    This advisory is available at the following link:

Affected Products

  o Vulnerable Products

    This vulnerability affects the following releases of ConfD if the built-in
    SSH server for CLI is enabled:

       Releases 7.4 through 7.4.3
       Releases 7.5 through 7.5.2

    To determine whether the built-in SSH server is enabled, see Section 4.1.1,
    "Disable built-in support for SSH in ConfD," in the ConfD and High Security
    Applications V2 application note.

    Products Confirmed Not Vulnerable

    Only products listed in the Vulnerable Products section of this advisory
    are known to be affected by this vulnerability.


  o There are no workarounds that address this vulnerability. However, a
    mitigation is available.

    Administrators can disable the ConfD built-in SSH server and use an
    external SSH server such as OpenSSH. For guidance on disabling the built-in
    support of SSH in ConfD, see Section 4.1.1, "Disable built-in support for
    SSH in ConfD," in the ConfD and High Security Applications V2 application

    While this mitigation has been deployed and was proven successful in a test
    environment, customers should determine the applicability and effectiveness
    in their own environment and under their own use conditions. Customers
    should be aware that any workaround or mitigation that is implemented may
    negatively impact the functionality or performance of their network based
    on intrinsic customer deployment scenarios and limitations. Customers
    should not deploy any workarounds or mitigations before first evaluating
    the applicability to their own environment and any impact to such

Fixed Software

  o Tail-f, a Cisco company, has released software updates that address the
    vulnerability described in this advisory. Customers may only install and
    expect support for software versions and feature sets for which they have a
    current license and have a valid support and maintenance agreement. By
    installing, downloading, accessing, or otherwise using such software
    upgrades, customers agree to follow the terms of their license agreement
    with Tail-f Systems AB. Security software updates do not entitle customers
    to a new software license or additional software feature sets.

    When considering software upgrades, customers are advised to regularly
    consult the advisories for Cisco products, which are available from the
    Cisco Security Advisories page , to determine exposure and a complete
    upgrade solution.

    Customers who have a current license and have a valid support and
    maintenance agreement can download the fixed version of software from their
    existing Tail-f delivery server download account.

    In all cases, customers should ensure that the devices to be upgraded
    contain sufficient memory and confirm that current hardware and software
    configurations will continue to be supported properly by the new release.
    If the information is not clear, customers are advised to open a support
    ticket in the Tail-f Support system.

    Fixed Releases

    This vulnerability is fixed in ConfD releases and later and
    releases and later.

Exploitation and Public Announcements

  o The Cisco Product Security Incident Response Team (PSIRT) is not aware of
    any public announcements or malicious use of the vulnerability that is
    described in this advisory.


  o This vulnerability was found during the resolution of a Cisco TAC support

Cisco Security Vulnerability Policy

  o To learn about Cisco security vulnerability disclosure policies and
    publications, see the Security Vulnerability Policy . This document also
    contains instructions for obtaining fixed software and receiving security
    vulnerability information from Cisco.


  o https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-confd-priv-esc-LsGtCRx4

Revision History

  o +----------+---------------------------+----------+--------+--------------+
    | Version  |        Description        | Section  | Status |     Date     |
    | 1.0      | Initial public release.   | -        | Final  | 2021-AUG-04  |

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