CVE-2020-11939: Integer Overflow or Wraparound (CWE-190)
value: In nDPI through 3.2 Stable, the SSH protocol dissector has multiple KEXINIT integer overflows that result in a controlled remote heap overflow in concat_hash_string in ssh.c. Due to the granular nature of the overflow primitive and the ability to control both the contents and layout of the nDPI library's heap memory through remote input, this vulnerability may be abused to achieve full Remote Code Execution against any network inspection stack that is linked against nDPI and uses it to perform network traffic analysis.
CWE description: The product performs a calculation that can
         produce an integer overflow or wraparound when the logic
         assumes that the resulting value will always be larger than
         the original value. This occurs when an integer value is
         incremented to a value that is too large to store in the
         associated representation. When this occurs, the value may
         become a very small or negative number.
CVSS v3 base score: 9.8
Published: 2020-04-23T15:15Z
Repository: https://github.com/ntop/nDPI
Language: C
Files changed: src/lib/protocols/ssh.c
Commit date: 2020-04-02 16:48:35 +0200
Commit message: ssh: fixing unsigned overflow leading to heap overflow

cf GHSL-2020-051

Diff: diff --git a/src/lib/protocols/ssh.c b/src/lib/protocols/ssh.c
index 292433e5..849dbeed 100644
--- a/src/lib/protocols/ssh.c
+++ b/src/lib/protocols/ssh.c
@@ -93,11 +93,11 @@ static void ndpi_int_ssh_add_connection(struct ndpi_detection_module_struct
 
 /* ************************************************************************ */
 
 static u_int16_t concat_hash_string(struct ndpi_packet_struct *packet,
 				   char *buf, u_int8_t client_hash) {
-  u_int16_t offset = 22, buf_out_len = 0;
+  u_int32_t offset = 22, buf_out_len = 0;
   if(offset+sizeof(u_int32_t) >= packet->payload_packet_len)
     goto invalid_payload;
   u_int32_t len = ntohl(*(u_int32_t*)&packet->payload[offset]);
   offset += 4;
 
@@ -112,117 +112,119 @@ static u_int16_t concat_hash_string(struct ndpi_packet_struct *packet,
 
   if(offset+sizeof(u_int32_t) >= packet->payload_packet_len)
     goto invalid_payload;
   /* ssh.server_host_key_algorithms [None] */
   len = ntohl(*(u_int32_t*)&packet->payload[offset]);
+  if (len > UINT32_MAX - 4 - offset)
+    goto invalid_payload;
   offset += 4 + len;
 
   if(offset+sizeof(u_int32_t) >= packet->payload_packet_len)
     goto invalid_payload;
   /* ssh.encryption_algorithms_client_to_server [C] */
   len = ntohl(*(u_int32_t*)&packet->payload[offset]);
 
+  offset += 4;
   if(client_hash) {
-    offset += 4;
-
     if((offset >= packet->payload_packet_len) || (len >= packet->payload_packet_len-offset-1))
       goto invalid_payload;
 
     strncpy(&buf[buf_out_len], (const char *)&packet->payload[offset], len);
     buf_out_len += len;
     buf[buf_out_len++] = ';';
-    offset += len;
-  } else
-    offset += 4 + len;
+  }
+  if (len > UINT32_MAX - offset)
+    goto invalid_payload;
+  offset += len;
 
   if(offset+sizeof(u_int32_t) >= packet->payload_packet_len)
     goto invalid_payload;
   /* ssh.encryption_algorithms_server_to_client [S] */
   len = ntohl(*(u_int32_t*)&packet->payload[offset]);
 
+  offset += 4;
   if(!client_hash) {
-    offset += 4;
-
     if((offset >= packet->payload_packet_len) || (len >= packet->payload_packet_len-offset-1))
       goto invalid_payload;
 
     strncpy(&buf[buf_out_len], (const char *)&packet->payload[offset], len);
     buf_out_len += len;
     buf[buf_out_len++] = ';';
-    offset += len;
-  } else
-    offset += 4 + len;
+  }
+  if (len > UINT32_MAX - offset)
+    goto invalid_payload;
+  offset += len;
 
   if(offset+sizeof(u_int32_t) >= packet->payload_packet_len)
     goto invalid_payload;
   /* ssh.mac_algorithms_client_to_server [C] */
   len = ntohl(*(u_int32_t*)&packet->payload[offset]);
 
+  offset += 4;
   if(client_hash) {
-    offset += 4;
-
     if((offset >= packet->payload_packet_len) || (len >= packet->payload_packet_len-offset-1))
       goto invalid_payload;
 
     strncpy(&buf[buf_out_len], (const char *)&packet->payload[offset], len);
     buf_out_len += len;
     buf[buf_out_len++] = ';';
-    offset += len;
-  } else
-    offset += 4 + len;
+  }
+  if (len > UINT32_MAX - offset)
+    goto invalid_payload;
+  offset += len;
 
   if(offset+sizeof(u_int32_t) >= packet->payload_packet_len)
     goto invalid_payload;
   /* ssh.mac_algorithms_server_to_client [S] */
   len = ntohl(*(u_int32_t*)&packet->payload[offset]);
 
+  offset += 4;
   if(!client_hash) {
-    offset += 4;
-
     if((offset >= packet->payload_packet_len) || (len >= packet->payload_packet_len-offset-1))
       goto invalid_payload;
 
     strncpy(&buf[buf_out_len], (const char *)&packet->payload[offset], len);
     buf_out_len += len;
     buf[buf_out_len++] = ';';
-    offset += len;
-  } else
-    offset += 4 + len;
+  }
+  if (len > UINT32_MAX - offset)
+    goto invalid_payload;
+  offset += len;
 
   /* ssh.compression_algorithms_client_to_server [C] */
   if(offset+sizeof(u_int32_t) >= packet->payload_packet_len)
     goto invalid_payload;
   len = ntohl(*(u_int32_t*)&packet->payload[offset]);
 
+  offset += 4;
   if(client_hash) {
-    offset += 4;
-
     if((offset >= packet->payload_packet_len) || (len >= packet->payload_packet_len-offset-1))
       goto invalid_payload;
 
     strncpy(&buf[buf_out_len], (const char *)&packet->payload[offset], len);
     buf_out_len += len;
-    offset += len;
-  } else
-    offset += 4 + len;
+  }
+  if (len > UINT32_MAX - offset)
+    goto invalid_payload;
+  offset += len;
 
   if(offset+sizeof(u_int32_t) >= packet->payload_packet_len)
     goto invalid_payload;
   /* ssh.compression_algorithms_server_to_client [S] */
   len = ntohl(*(u_int32_t*)&packet->payload[offset]);
 
+  offset += 4;
   if(!client_hash) {
-    offset += 4;
-
     if((offset >= packet->payload_packet_len) || (len >= packet->payload_packet_len-offset-1))
       goto invalid_payload;
 
     strncpy(&buf[buf_out_len], (const char *)&packet->payload[offset], len);
     buf_out_len += len;
-    offset += len;
-  } else
-    offset += 4 + len;
+  }
+  if (len > UINT32_MAX - offset)
+    goto invalid_payload;
+  offset += len;
 
   /* ssh.languages_client_to_server [None] */
 
   /* ssh.languages_server_to_client [None] */
 

Vulnerable code:   u_int16_t offset = 22, buf_out_len = 0;
    offset += 4;

    offset += len;
  } else
    offset += 4 + len;
    offset += 4;

    offset += len;
  } else
    offset += 4 + len;
    offset += 4;

    offset += len;
  } else
    offset += 4 + len;
    offset += 4;

    offset += len;
  } else
    offset += 4 + len;
    offset += 4;

    offset += len;
  } else
    offset += 4 + len;
    offset += 4;

    offset += len;
  } else
    offset += 4 + len;
Fixed code:   u_int32_t offset = 22, buf_out_len = 0;
  if (len > UINT32_MAX - 4 - offset)
    goto invalid_payload;
  offset += 4;
  }
  if (len > UINT32_MAX - offset)
    goto invalid_payload;
  offset += len;
  offset += 4;
  }
  if (len > UINT32_MAX - offset)
    goto invalid_payload;
  offset += len;
  offset += 4;
  }
  if (len > UINT32_MAX - offset)
    goto invalid_payload;
  offset += len;
  offset += 4;
  }
  if (len > UINT32_MAX - offset)
    goto invalid_payload;
  offset += len;
  offset += 4;
  }
  if (len > UINT32_MAX - offset)
    goto invalid_payload;
  offset += len;
  offset += 4;
  }
  if (len > UINT32_MAX - offset)
    goto invalid_payload;
  offset += len;