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AUSCERT External Security Bulletin Redistribution
Cisco Jabber for Windows DLL Preloading Vulnerability
4 July 2019
AusCERT Security Bulletin Summary
Product: Cisco Jabber for Windows
Publisher: Cisco Systems
Operating System: Windows
Impact/Access: Execute Arbitrary Code/Commands -- Existing Account
CVE Names: CVE-2019-1855
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Cisco Jabber for Windows DLL Preloading Vulnerability
Advisory ID: cisco-sa-20190703-jabber-dll
First Published: 2019 July 3 16:00 GMT
Version 1.0: Final
Workarounds: No workarounds available
Cisco Bug IDs: CSCvo55994CSCvo63008
o A vulnerability in the loading mechanism of specific dynamic link libraries
in Cisco Jabber for Windows could allow an authenticated, local attacker to
perform a DLL preloading attack. To exploit this vulnerability, the
attacker would need to have valid credentials on the Windows system.
The vulnerability is due to insufficient validation of the resources loaded
by the application at run time. An attacker could exploit this
vulnerability by crafting a malicious DLL file and placing it in a specific
location on the targeted system. The malicious DLL file would execute when
the Jabber application launches. A successful exploit could allow the
attacker to execute arbitrary code on the target machine with the
privileges of another user's account.
Cisco has released software updates that address this vulnerability. There
are no workarounds that address this vulnerability.
This advisory is available at the following link:
o Vulnerable Products
This vulnerability affects all Cisco Jabber for Windows software releases
prior to 12.6(0).
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
Jabber for Android
Jabber for iPhone and iPad
Jabber for Mac
o There are no workarounds that address this vulnerability.
o Cisco has released free 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 purchased a
license. By installing, downloading, accessing, or otherwise using such
software upgrades, customers agree to follow the terms of the Cisco
Additionally, customers may only download software for which they have a
valid license, procured from Cisco directly, or through a Cisco authorized
reseller or partner. In most cases this will be a maintenance upgrade to
software that was previously purchased. Free security software updates do
not entitle customers to a new software license, additional software
feature sets, or major revision upgrades.
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
Customers Without Service Contracts
Customers who purchase directly from Cisco but do not hold a Cisco service
contract and customers who make purchases through third-party vendors but
are unsuccessful in obtaining fixed software through their point of sale
should obtain upgrades by contacting the Cisco TAC:
Customers should have the product serial number available and be prepared
to provide the URL of this advisory as evidence of entitlement to a free
This vulnerability is fixed in Cisco Jabber for Windows 12.6(0) 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 Cisco would like to thank security researcher "wjcsharp" for reporting this
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.
| Version | Description | Section | Status | Date |
| 1.0 | Initial public release. | - | Final | 2019-July-03 |
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