1528
return f.getCanonicalPath();
}
The problem with the above code is that the validation step occurs before canonicalization occurs.
An attacker could provide an input path of "/safe_dir/../" that would pass the validation step.
However, the canonicalization process sees the double dot as a traversal to the parent directory
and hence when canonicized the path would become just "/".
To avoid this problem, validation should occur after canonicalization takes place. In this case
canonicalization occurs during the initialization of the File object. The code below fixes the issue.
Example Language: Java (Good)
String path = getInputPath();
File f = new File(path);
if (f.getCanonicalPath().startsWith("/safe_dir/"))
{
return f.getCanonicalPath();
}
Example 2:
This function prints the contents of a specified file requested by a user.
Example Language: PHP (Bad)
function printFile($username,$filename){
//read file into string
$file = file_get_contents($filename);
if ($file && isOwnerOf($username,$filename)){
echo $file;
return true;
}
else{
echo 'You are not authorized to view this file';
}
return false;
}
This code first reads a specified file into memory, then prints the file if the user is authorized to see
its contents. The read of the file into memory may be resource intensive and is unnecessary if the
user is not allowed to see the file anyway.
Example 3:
Assume that the module foo_bar implements a protected register. The register content is the
asset. Only transactions made by user id (indicated by signal usr_id) 0x4 are allowed to modify the
register contents. The signal grant_access is used to provide access.
Example Language: Verilog (Bad)
module foo_bar(data_out, usr_id, data_in, clk, rst_n);
output reg [7:0] data_out;
input wire [2:0] usr_id;
input wire [7:0] data_in;
input wire clk, rst_n;
wire grant_access;
always @ (posedge clk or negedge rst_n)
begin
if (!rst_n)
data_out = 0;
else
data_out = (grant_access) ? data_in : data_out;
assign grant_access = (usr_id == 3'h4) ? 1'b1 : 1'b0;
end
CWE Version 4.14
CWE-696: Incorrect Behavior Order
CWE-696: Incorrect Behavior Order