ESB-2018.0922 - [Cisco] Cisco IOS: Denial of service - Remote/unauthenticated 2018-03-29

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             AUSCERT External Security Bulletin Redistribution

                               ESB-2018.0922
        Cisco IOS Software Login Enhancements Login Block Denial of
                          Service Vulnerabilities
                               29 March 2018

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        AusCERT Security Bulletin Summary
        ---------------------------------

Product:           Cisco IOS
Publisher:         Cisco Systems
Operating System:  Cisco
Impact/Access:     Denial of Service -- Remote/Unauthenticated
Resolution:        Patch/Upgrade
CVE Names:         CVE-2018-0180 CVE-2018-0179 

Original Bulletin: 
   https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180328-slogin

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Cisco Security Advisory

Cisco IOS Software Login Enhancements Login Block Denial of Service
Vulnerabilities

Medium

Advisory ID:     cisco-sa-20180328-slogin

First Published: 2018 March 28 16:00 GMT

Version 1.0:     Final

Workarounds:     No workarounds available

Cisco Bug IDs:
CSCuy32360
CSCuz60599

CVE-2018-0179
CVE-2018-0180

CWE-399

CVSS Score:
6.8  AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X

Summary

  o Multiple vulnerabilities in the Login Enhancements (Login Block) feature of
    Cisco IOS Software could allow an unauthenticated, remote attacker to
    trigger a reload of an affected system, resulting in a denial of service
    (DoS) condition.

    For more information about these vulnerabilities, see the Details section
    of this security advisory.

    There are no workarounds that address both vulnerabilities.

    This advisory is available at the following link:
    https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/
    cisco-sa-20180328-slogin

Affected Products

  o Vulnerable Products

    These vulnerabilities affect Cisco devices that are running Cisco IOS
    Software Release 15.4(2)T, 15.4(3)M, or 15.4(2)CG and later.

    Determining the Cisco IOS Software Release

    To determine which Cisco IOS Software release is running on a device,
    administrators can log in to the device, use the show version command in
    the CLI, and then refer to the system banner that appears. If the device is
    running Cisco IOS Software, the system banner displays text similar to
    Cisco Internetwork Operating System Software or Cisco IOS Software. The
    banner also displays the installed image name in parentheses, followed by
    the Cisco IOS Software release number and release name. Some Cisco devices
    do not support the show version command or may provide different output.

    The following example shows the output of the command for a device that is
    running Cisco IOS Software Release 15.5(2)T1 and has an installed image
    name of C2951-UNIVERSALK9-M:

        Router> show version

        Cisco IOS Software, C2951 Software (C2951-UNIVERSALK9-M), Version 15.5(2)T1, RELEASE SOFTWARE (fc1)
        Technical Support: http://www.cisco.com/techsupport
        Copyright (c) 1986-2015 by Cisco Systems, Inc.
        Compiled Mon 22-Jun-15 09:32 by prod_rel_team
        .
        .
        .

    For information about the naming and numbering conventions for Cisco IOS
    Software releases, see the Cisco IOS and NX-OS Software Reference Guide.

    Products Confirmed Not Vulnerable

    No other Cisco products are currently known to be affected by these
    vulnerabilities.

    Cisco has confirmed that these vulnerabilities do not affect IOS XE
    Software, Cisco IOS XR Software, or Cisco NX-OS Software.

Details

  o The Cisco IOS Login Enhancements (Login Block) Feature

    The Cisco IOS Login Enhancements (Login Block) feature allows users to
    enhance the security of a router by configuring options to automatically
    block further login attempts when a possible DoS attack is detected.

    The login block and login delay options introduced by this feature can be
    configured for Telnet or SSH virtual connections. By enabling this feature,
    you can slow down "dictionary attacks" by enforcing a "quiet period" if
    multiple failed connection attempts are detected, thereby protecting the
    routing device from a type of DoS attack.

    Further information on the Login Enhancements (Login Block) feature is
    available in the Cisco IOS Security Configuration Guide.

    Vulnerability Details

    Two vulnerabilities in the Login Enhancements (Login Block) feature of
    Cisco IOS Software could allow an unauthenticated, remote attacker to
    trigger a reload of an affected device, resulting in a denial of service
    (DoS) condition.

    The vulnerabilities are not dependent on one another; exploitation of one
    of the vulnerabilities is not required to exploit the other vulnerability.
    In addition, a software release that is affected by one of the
    vulnerabilities may not be affected by the other vulnerability.

    Details about the vulnerabilities are as follows.

    Cisco IOS Software Login Block Denial of Service Vulnerability

    A vulnerability in the Login Enhancements (Login Block) feature of
    Cisco IOS Software could allow an unauthenticated, remote attacker to
    trigger a reload of an affected system, resulting in a denial of service
    (DoS) condition.

    The vulnerability is due to an attempt to free an area of memory that has
    not been previously allocated. An attacker could exploit this vulnerability
    by attempting to log in to an affected device via Secure Shell (SSH) or
    Telnet with invalid credentials multiple times.

    This vulnerability is exploitable only if both of the following conditions
    are met:

       login quiet-mode access-class has been configured prior to configuring
        login block-for. These features are not enabled by default.
       The device has not been reloaded since that configuration occurred.

    The Common Vulnerabilities and Exposures (CVE) ID for this vulnerability
    is: CVE-2018-0179

    The Security Impact Rating (SIR) for this vulnerability is: Medium

    The Cisco bug ID for this vulnerability is: CSCuy32360

    Cisco IOS Software Login Block Denial of Service Vulnerability

    A vulnerability in the Login Enhancements (Login Block) feature of
    Cisco IOS Software could allow an unauthenticated, remote attacker to
    trigger a reload of an affected system, resulting in a denial of service
    (DoS) condition.

    The vulnerability is due to an attempt to free an area of memory that has
    not been previously allocated. An attacker could exploit this vulnerability
    by attempting to log in to an affected device via SSH or Telnet with
    invalid credentials multiple times while the administrator modifies the
    login block-for configuration.

    This vulnerability is exploitable only if login block-for has been
    configured on an affected device. This feature is not enabled by default.

    The CVE ID for this vulnerability is: CVE-2018-0180

    The SIR for this vulnerability is: Medium

    The Cisco bug ID for this vulnerability is: CSCuz60599

Indicators of Compromise

  o The following conditions can indicate that a compromise has occurred.

    Cisco IOS Software Login Block Denial of Service Vulnerability - CSCuy32360

    Immediately before the device crashes and reloads, the device will log
    messages similar to the following example at least twice:

        %SEC_LOGIN-4-LOGIN_FAILED: Login failed [user: USERNAME] [Source: xx.xx.xx.xx [localport: 22] [Reason: Login Authentication Failed] at 03:37:06 UTC Sat Feb 13 2016
        %SEC_LOGIN-1-QUIET_MODE_ON: Still timeleft for watching failures is 52 secs, [user: USERNAME] [Source: xx.xx.xx.xx] [localport: 22] [Reason: Login Authentication Failed] [ACL: LOGIN_ACL] at 03:37:06 UTC Sat Feb 13 2016

    Exploitation of this vulnerability will cause an affected device to
    generate a crashinfo file. Contact the Cisco Technical Assistance Center
    (TAC) to review the output of the show tech-support command and the
    crashinfo file to determine whether the device has been compromised by
    exploitation of this vulnerability.

    Cisco IOS Software Login Block Denial of Service Vulnerability - CSCuz60599

    After this vulnerability has been exploited on an affected system, the
    device will log an error message about a bad chunk reference count in
    process Secure Login similar to the following example:

        %SYS-2-CHUNKBADREFCOUNT: Bad chunk reference count, chunk 3F57D864 data 3F589728 refcount FFFFFFFF alloc pc 323635BC. -Process= "Secure Login", ipl= 0, pid= 388

    Exploitation of this vulnerability will cause an affected device to
    generate a crashinfo file. Contact the Cisco Technical Assistance Center
    (TAC) to review the output of the show tech-support command and the
    crashinfo file to determine whether the device has been compromised by
    exploitation of this vulnerability.

Workarounds

  o As a workaround for the vulnerability described in CSCuy32360,
    administrators can take one of the following actions:

       Configure login block-for prior to configuring login quiet-mode
        access-class
       Ensure that the device is reloaded after login block-for and login
        quiet-mode access-class are configured

    There are no workarounds that address the vulnerability described in
    CSCuz60599.

Fixed Software

  o For detailed information about fixed software releases, consult the Cisco
    bug ID(s) at the top of this advisory.

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

    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 contact the Cisco
    Technical Assistance Center (TAC) or their contracted maintenance
    providers.

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 vulnerabilities that are
    described in this advisory.

Source

  o These vulnerabilities were found during the resolution of Cisco TAC support
    cases.

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.

Subscribe to Cisco Security Notifications

  o Subscribe

URL

  o https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180328-slogin

Revision History

  o 
    +----------+----------------------------+----------+---------+----------------+
    | Version  |        Description         | Section  | Status  |      Date      |
    +----------+----------------------------+----------+---------+----------------+
    | 1.0      | Initial public release.    | --       | Final   | 2018-March-28  |
    +----------+----------------------------+----------+---------+----------------+

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