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Why Cisco's DCNM Is in a World of Trouble

Vendor's Data Center Network Manager (DCNM) has racked up three critical authentication bypass vulnerabilities at the top of the list of 12 separate problems that were announced on January 2.

Larry Loeb

January 6, 2020

3 Min Read

Cisco's Data Center Network Manager (DCNM) has been found to be in a world of trouble, racking up three critical authentication bypass vulnerabilities at the top of the list of 12 separate problems that were announced on January 2, 2020. These three have a CVSS of 9.8 out of 10, so they are serious.

Cisco says in a security advisory about the problems that the vulnerabilities "could allow an unauthenticated, remote attacker to bypass authentication and execute arbitrary actions with administrative privileges on an affected device."

While Cisco has released software updates that it says will address and fix the reported problems, there are "no workarounds that address these vulnerabilities."

These vulnerabilities affect Cisco DCNM software releases earlier than Release 11.3(1) for Microsoft Windows, Linux and virtual appliance platforms.

The vulnerabilities are said by Cisco to not be dependent on one another. That means that exploitation of one of the vulnerabilities is not required to exploit another vulnerability. Cisco also says that a software release which is affected by one of the vulnerabilities may not be affected by the other vulnerabilities.

One of the vulnerabilities (CVE-2019-15975) is in the REST API endpoint of Cisco DCNM. Cisco says that the vulnerability exists because "a static encryption key is shared between installations." That means that an attacker could exploit it by using the static key to craft a valid session token. A successful exploit could then allow the attacker to perform arbitrary actions by use of the REST API with administrative privileges.

CVE-2019-15976 is basically the same problem of a static key existing between installations, but in the SOAP API endpoint of Cisco DCNM. The same results of remote attack could occur through the use of a differing API than before.

A vulnerability (CVE-2019-15977) is also present in the web-based management interface of Cisco DCNM that could once again allow an unauthenticated, remote attacker to bypass authentication on an affected device.

This time it's the presence of static credentials causing the problem. An attacker could use the static credentials to authenticate malware that attacks through the user interface. A successful attack could then access a specific section of the web interface and obtain confidential information from an affected device. This information could be used in further attacks against the system.

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

Security firm Tenable says that by utilizing these authentication bypass vulnerabilities, attackers could in their exploits leverage the remaining flaws patched by Cisco, which include command injection vulnerabilities (CVE-2019-15978, CVE-2019-15979), SQL injection vulnerabilities (CVE-2019-15984, CVE-2019-15985), path traversal vulnerabilities (CVE-2019-15980, CVE-15981, CVE-2019-15982) and an XML external entity vulnerability (CVE-2019-15983).

Eleven of the vulnerabilities were discovered and reported to Cisco by Steven Seeley of Source Incite. Cisco's software update also patched CVE-2019-15999, which is a vulnerability in the DCNM's JBoss Enterprise Application Platform (EAP) reported by Harrison Neal of PatchAdvisor. The authentication settings on the EAP were evidently incorrectly configured.

— Larry Loeb has written for many of the last century's major "dead tree" computer magazines, having been, among other things, a consulting editor for BYTE magazine and senior editor for the launch of WebWeek.

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About the Author(s)

Larry Loeb

Blogger, Informationweek

Larry Loeb has written for many of the last century's major "dead tree" computer magazines, having been, among other things, a consulting editor for BYTE magazine and senior editor for the launch of WebWeek. He has written a book on the Secure Electronic Transaction Internet protocol. His latest book has the commercially obligatory title of Hack Proofing XML. He's been online since uucp "bang" addressing (where the world existed relative to !decvax), serving as editor of the Macintosh Exchange on BIX and the VARBusiness Exchange. His first Mac had 128 KB of memory, which was a big step up from his first 1130, which had 4 KB, as did his first 1401. You can e-mail him at [email protected].

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