CVE-2018-9336 (published 2018-05-01T18:29Z)

openvpnserv.exe (aka the interactive service helper) in OpenVPN 2.4.x before 2.4.6 allows a local attacker to cause a double-free of memory by sending a malformed request to the interactive service. This could cause a denial-of-service through memory corruption or possibly have unspecified other impact including privilege escalation.

Severity: MEDIUM
CVSS v2 base score: 4.6 (AV:L/AC:L/Au:N/C:P/I:P/A:P)
CVSS v3 base score: 7.8, HIGH (CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)

Weakness information:
cwe_id: CWE-415
cwe_name: Double Free
description: The product calls free() twice on the same memory address, potentially leading to modification of unexpected memory locations.
extended_description: When a program calls free() twice with the same argument, the program's memory management data structures become corrupted. This corruption can cause the program to crash or, in some circumstances, cause two later calls to malloc() to return the same pointer. If malloc() returns the same value twice and the program later gives the attacker control over the data that is written into this doubly-allocated memory, the program becomes vulnerable to a buffer overflow attack.
         

Fix information:
repo_url: https://github.com/OpenVPN/openvpn
commit_details: repo_url: https://github.com/OpenVPN/openvpn
author: Gert Doering
author_date: 2018-04-14 09:26:17+02:00
msg: Fix potential double-free() in Interactive Service (CVE-2018-9336)

Malformed input data on the service pipe towards the OpenVPN interactive
service (normally used by the OpenVPN GUI to request openvpn instances
from the service) can result in a double free() in the error handling code.

This usually only leads to a process crash (DoS by an unprivileged local
account) but since it could possibly lead to memory corruption if
happening while multiple other threads are active at the same time,
CVE-2018-9336 has been assigned to acknowledge this risk.

Fix by ensuring that sud->directory is set to NULL in GetStartUpData()
for all error cases (thus not being free()ed in FreeStartupData()).

Rewrite control flow to use explicit error label for error exit.

Discovered and reported by Jacob Baines <jbaines@tenable.com>.

CVE: 2018-9336

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Selva Nair <selva.nair@gmail.com>
Message-Id: <20180414072617.25075-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/search?l=mid&q=20180414072617.25075-1-gert@greenie.muc.de

Signed-off-by: Gert Doering <gert@greenie.muc.de>
repository: repo_url: https://github.com/OpenVPN/openvpn
repo_name: OpenVPN/openvpn
description: OpenVPN  is  an open source VPN daemon
repo_language: C
owner: OpenVPN
file_changes: filename: interactive.c
change_type: ModificationType.MODIFY
diff: @@ -453,7 +453,6 @@ static BOOL
 GetStartupData(HANDLE pipe, STARTUP_DATA *sud)
 {
     size_t size, len;
-    BOOL ret = FALSE;
     WCHAR *data = NULL;
     DWORD bytes, read;
 
@@ -462,7 +461,7 @@ GetStartupData(HANDLE pipe, STARTUP_DATA *sud)
     {
         MsgToEventLog(M_SYSERR, TEXT("PeekNamedPipeAsync failed"));
         ReturnLastError(pipe, L"PeekNamedPipeAsync");
-        goto out;
+        goto err;
     }
 
     size = bytes / sizeof(*data);
@@ -470,7 +469,7 @@ GetStartupData(HANDLE pipe, STARTUP_DATA *sud)
     {
         MsgToEventLog(M_SYSERR, TEXT("malformed startup data: 1 byte received"));
         ReturnError(pipe, ERROR_STARTUP_DATA, L"GetStartupData", 1, &exit_event);
-        goto out;
+        goto err;
     }
 
     data = malloc(bytes);
@@ -478,7 +477,7 @@ GetStartupData(HANDLE pipe, STARTUP_DATA *sud)
     {
         MsgToEventLog(M_SYSERR, TEXT("malloc failed"));
         ReturnLastError(pipe, L"malloc");
-        goto out;
+        goto err;
     }
 
     read = ReadPipeAsync(pipe, data, bytes, 1, &exit_event);
@@ -486,14 +485,14 @@ GetStartupData(HANDLE pipe, STARTUP_DATA *sud)
     {
         MsgToEventLog(M_SYSERR, TEXT("ReadPipeAsync failed"));
         ReturnLastError(pipe, L"ReadPipeAsync");
-        goto out;
+        goto err;
     }
 
     if (data[size - 1] != 0)
     {
         MsgToEventLog(M_ERR, TEXT("Startup data is not NULL terminated"));
         ReturnError(pipe, ERROR_STARTUP_DATA, L"GetStartupData", 1, &exit_event);
-        goto out;
+        goto err;
     }
 
     sud->directory = data;
@@ -503,7 +502,7 @@ GetStartupData(HANDLE pipe, STARTUP_DATA *sud)
     {
         MsgToEventLog(M_ERR, TEXT("Startup data ends at working directory"));
         ReturnError(pipe, ERROR_STARTUP_DATA, L"GetStartupData", 1, &exit_event);
-        goto out;
+        goto err;
     }
 
     sud->options = sud->directory + len;
@@ -513,16 +512,16 @@ GetStartupData(HANDLE pipe, STARTUP_DATA *sud)
     {
         MsgToEventLog(M_ERR, TEXT("Startup data ends at command line options"));
         ReturnError(pipe, ERROR_STARTUP_DATA, L"GetStartupData", 1, &exit_event);
-        goto out;
+        goto err;
     }
 
     sud->std_input = sud->options + len;
-    data = NULL; /* don't free data */
-    ret = TRUE;
+    return TRUE;
 
-out:
+err:
+    sud->directory = NULL;		/* caller must not free() */
     free(data);
-    return ret;
+    return FALSE;
 }
 
 

programming_language: C