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.
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.
Threat Mapped score: 0.0
Industry: Finiancial
Threat priority: Unclassified
CVE: CVE-2019-10071
Java-oriented framework compares HMAC signatures using String.equals() instead of a constant-time algorithm, causing timing discrepancies
CVE: CVE-2019-10482
Smartphone OS uses comparison functions that are not in constant time, allowing side channels
CVE: 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 attack that relies on timing differences in responses to incorrect password guesses, aka a timing side-channel attack.
CVE: 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 cryptographic attacks that rely on distinguishing between padding and MAC verification errors, possibly leading to extraction of the original plaintext, aka the "Vaudenay timing attack."
CVE: 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.
CVE: CVE-2003-0637
Product uses a shorter timeout for a non-existent user than a valid user, which makes it easier for remote attackers to guess usernames and conduct brute force password guessing.
CVE: CVE-2003-0190
Product immediately sends an error message when a user does not exist, which allows remote attackers to determine valid usernames via a timing attack.
CVE: CVE-2004-1602
FTP server responds in a different amount of time when a given username exists, which allows remote attackers to identify valid usernames by timing the server response.
CVE: CVE-2005-0918
Browser allows remote attackers to determine the existence of arbitrary files by setting the src property to the target filename and using Javascript to determine if the web page immediately stops loading, which indicates whether the file exists or not.
| Phase | Note |
|---|---|
| Architecture and Design | COMMISSION: This weakness refers to an incorrect design related to an architectural security tactic. |
| Implementation | N/A |
| Operation | N/A |
Intro: 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.
Body: 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; break; end assign grant_access = (check_pass == 4'b1111) ? 1'b1: 1'b0; endIntro: In this example, the attacker observes how long an authentication takes when the user types in the correct password.
Body: 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): if actual_pw[i] <> typed_pw[i]: return 0 return 1