CWE-208: Observable Timing Discrepancy

Description:
Two separate operations in a product require different amounts of time to complete, in a way that is observable to an actor and reveals security-relevant information about the state of the product, such as whether a particular operation was successful or not.

Extended Description:
In security-relevant contexts, even small variations in timing can be exploited by attackers to indirectly infer certain details about the product's internal operations.  For example, in some cryptographic algorithms, attackers can use timing differences to infer certain properties about a private key, making the key easier to guess.  Timing discrepancies effectively form a timing side channel.

Affected languages: Not Language-Specific
Affected technologies: Not Technology-Specific
Parent weaknesses: CWE-203

Consequences:
  - Confidentiality: Read Application Data

Demonstrative examples:
Consider an example hardware module that checks a user-provided password to grant access to a user. The user-provided password is compared against a golden value in a byte-by-byte manner.
Since the code breaks on an incorrect entry of password, an attacker can guess the correct password for that byte-check iteration with few repeat attempts.
always_comb @ (posedge clk) 
                     
                    begin 
		     
                      assign check_pass[3:0] = 4'b0; 
                      for (i = 0; i < 4; i++) begin 
		       
                    	if (entered_pass[(i*8 - 1) : i] eq golden_pass([i*8 - 1) : i]) 
			 
			  assign check_pass[i] = 1; 
                    	  continue; 
			 
                    	else 
			 
                    	  assign check_pass[i] = 0; 
          

In this example, the attacker observes how long an authentication takes when the user types in the correct password.
When the attacker tries their own values, they can first try strings of various length. When they find a string of the right length, the computation will take a bit longer, because the for loop will run at least once. Additionally, with this code, the attacker can possibly learn one character of the password at a time, because when they guess the first character right, the computation will take longer than a wrong guesses. Such an attack can break even the most sophisticated password with a few hundred guesses.
def validate_password(actual_pw, typed_pw):
		  
                    if len(actual_pw) <> len(typed_pw):
		    return 0 
                    for i in len(actual_pw):


Real-world examples:
  - CVE-2019-10071: Java-oriented framework compares HMAC signatures  using  String.equals() instead of a constant-time algorithm, causing timing discrepancies
  - CVE-2019-10482: Smartphone OS uses comparison functions that are not in constant time, allowing side channels
  - CVE-2014-0984: Password-checking function in router terminates validation of a password entry when it encounters the first incorrect character, which allows remote attackers to obtain passwords via a brute-force att
  - CVE-2003-0078: SSL implementation does not perform a MAC computation if an incorrect block cipher padding is used, which causes an information leak (timing discrepancy) that may make it easier to launch cryptographi
  - CVE-2000-1117: Virtual machine allows malicious web site operators to determine the existence of files on the client by measuring delays in the execution of the getSystemResource method.