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AUSCERT External Security Bulletin Redistribution
ESB-2024.1855
Cisco IOS XE Software Auxiliary Asynchronous Port Denial of Service
Vulnerability
28 March 2024
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AusCERT Security Bulletin Summary
---------------------------------
Product: Cisco IOS XE Software
Publisher: Cisco Systems
Operating System: Cisco
Resolution: Patch/Upgrade
CVE Names: CVE-2024-20309
Original Bulletin:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-aux-333WBz8f
Comment: CVSS (Max): 5.6 CVE-2024-20309 (CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:N/I:N/A:H)
CVSS Source: Cisco Systems
Calculator: https://www.first.org/cvss/calculator/3.1#CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:N/I:N/A:H
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Cisco IOS XE Software Auxiliary Asynchronous Port Denial of Service
Vulnerability
Priority: Medium
Advisory ID: cisco-sa-aux-333WBz8f
First Published: 2024 March 27 16:00 GMT
Version 1.0: Final
Workarounds: Yes
Cisco Bug IDs: CSCwh47363
CVE Names: CVE-2024-20309
CWEs: CWE-828
Summary
o A vulnerability in auxiliary asynchronous port (AUX) functions of Cisco IOS
XE Software could allow an authenticated, local attacker to cause an
affected device to reload or stop responding.
This vulnerability is due to the incorrect handling of specific ingress
traffic when flow control hardware is enabled on the AUX port. An attacker
could exploit this vulnerability by reverse telnetting to the AUX port and
sending specific data after connecting. A successful exploit could allow
the attacker to cause the device to reset or stop responding, resulting in
a denial of service (DoS) condition.
Cisco has released software updates that address this vulnerability. There
are workarounds that address this vulnerability.
This advisory is available at the following link:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-aux-333WBz8f
This advisory is part of the March 2024 release of the Cisco IOS and IOS XE
Software Security Advisory Bundled Publication. For a complete list of the
advisories and links to them, see Cisco Event Response: March 2024
Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled
Publication .
Affected Products
o Vulnerable Products
At the time of publication, this vulnerability affected Cisco platforms if
they were running a vulnerable release of Cisco IOS XE Software and the
following conditions were true:
The device has an AUX port.
The AUX port is configured with flowcontrol hardware .
There is no hardware attached to the AUX port or the attached modem has
signaled for flow control to be off and does not turn it on again.
For information about which Cisco software releases were vulnerable at the
time of publication, see the Fixed Software section of this advisory.
Determine the AUX Port Configuration
To determine whether the device has an AUX port and whether flowcontrol
hardware is enabled, log in to the system and use the show running-config |
section aux 0 CLI command to check for the presence of the flowcontrol
hardware and transport input all|telnet commands. If these are present, as
shown in the following example, the device is considered vulnerable if
either no hardware is attached or if the attached modem has signaled for
flow control to be off and does not turn it back on:
Router#show running-config | section line aux 0
line aux 0
transport input all
transport output none
flowcontrol hardware
Router#
If the output does not contain flowcontrol hardware or is blank, as shown
in the following example, the device is not affected by this vulnerability:
Switch#show running-config | section line aux 0
Switch#
Products Confirmed Not Vulnerable
Only products listed in the Vulnerable Products section of this advisory
are known to be affected by this vulnerability.
Cisco has confirmed that this vulnerability does not affect the following
Cisco products:
IOS Software
IOS XR Software
Meraki products
NX-OS Software
Workarounds
o There is a workaround that addresses this vulnerability.
If the AUX port is not being used, it should be disabled, as shown in the
following example:
Router# show running-config | section line aux 0
line aux 0
transport input none
transport output none
no exec
Router#
While this workaround 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
environment.
Fixed Software
o 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.
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.
Cisco IOS and IOS XE Software
To help customers determine their exposure to vulnerabilities in Cisco IOS
and IOS XE Software, Cisco provides the Cisco Software Checker . This tool
identifies any Cisco security advisories that impact a specific software
release and the earliest release that fixes the vulnerabilities that are
described in each advisory ("First Fixed"). If applicable, the tool also
returns the earliest release that fixes all the vulnerabilities that are
described in all the advisories that the Software Checker identifies
("Combined First Fixed").
To use the tool, go to the Cisco Software Checker page and follow the
instructions. Alternatively, use the following form to determine whether a
release is affected by any Cisco Security Advisory. To use the form, follow
these steps:
1. Choose which advisories the tool will search-only this advisory, only
advisories with a Critical or High Security Impact Rating (SIR) , or
all advisories.
2. Enter a release number-for example, 15.9(3)M2 or 17.3.3.
3. Click Check .
[2 ] [ ] [Critical,High,Medium]
[Only this advisory ]
[ ] [Check]
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.
Source
o This vulnerability was found during internal security testing.
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
Related to This Advisory
o Cisco Event Response: March 2024 Semiannual Cisco IOS and IOS XE Software
Security Advisory Bundled Publication
URL
o https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-aux-333WBz8f
Revision History
o +----------+---------------------------+----------+--------+--------------+
| Version | Description | Section | Status | Date |
+----------+---------------------------+----------+--------+--------------+
| 1.0 | Initial public release. | - | Final | 2024-MAR-27 |
+----------+---------------------------+----------+--------+--------------+
Legal Disclaimer
o THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND
OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR
FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT
OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES
THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.
A standalone copy or paraphrase of the text of this document that omits the
distribution URL is an uncontrolled copy and may lack important information
or contain factual errors. The information in this document is intended for
end users of Cisco products.
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