A vulnerability, which was classified as critical, has been found in Microsoft Windows 7/10 (Operating System). Affected by this issue is an unknown code block of the file cmd.exe. The manipulation as part of a ASCII Substitute Character leads to a privileges management vulnerability. Using CWE to declare the problem leads to CWE-269. The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor. Impacted is confidentiality, integrity, and availability.

The weakness was disclosed 11/11/2016 by Julian Horoszkiewicz as Unexpected behavior of cmd.exe while processing .bat files leads to potential command injection vulnerabilities as not defined mailinglist post (Full-Disclosure). The advisory is available at seclists.org. The vendor was not involved in the coordination of the public release. The attack may be launched remotely. No form of authentication is required for exploitation. Technical details as well as a public exploit are known. The structure of the vulnerability defines a possible price range of USD $0-$5k at the moment (estimation calculated on 07/07/2019). This vulnerability is assigned to T1068 by the MITRE ATT&CK project. The advisory points out:

It was discovered that cmd.exe, when processing .bat files, treats the ASCII substitute character (code 26) as a command separator (like & or |). This opens the way for unexpected command injection vulnerabilities in applications which generate .bat files based on user input, as this character is not filtered by most application input sanitisers against command injection.

A public exploit has been developed by Julian Horoszkiewicz in HTTP POST Request and been published immediately after the advisory. The exploit is available at seclists.org. It is declared as proof-of-concept. As 0-day the estimated underground price was around $25k-$100k. The code used by the exploit is:

POST /escape_shell_cmd.php HTTP/1.1
Host: localhost
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:47.0) Gecko/20100101
Firefox/47.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: pl,en-US;q=0.7,en;q=0.3
Accept-Encoding: gzip, deflate
Connection: close
Content-Type: application/x-www-form-urlencoded
Content-Length: 35

dir=.%1anet user /add hacked hacked

Let's send a request containing "." as a parameter to the hardcoded "dir" command, appended with another command - taking advantage of %1a as a command separator.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

Productinfo

Type

• Operating System

Vendor

• Microsoft

Name

• Windows

Version

• 7
• 10

License

• commercial

CPE 2.3info

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CPE 2.2info

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