CWE-301 Base Draft Medium likelihood

Reflection Attack in an Authentication Protocol

A reflection attack is a flaw in mutual authentication protocols that allows an attacker to impersonate a legitimate user without knowing the secret key. This happens when an attacker can bounce, or…

Definition

What is CWE-301?

A reflection attack is a flaw in mutual authentication protocols that allows an attacker to impersonate a legitimate user without knowing the secret key. This happens when an attacker can bounce, or 'reflect,' a server's own challenge back to it using a second connection, tricking the system into granting access.
In a typical mutual authentication setup, both the client and server share a secret key. To prove identity without sending the key directly, they exchange random challenges that must be encrypted with that shared secret. The vulnerability arises when the same key is used across multiple sessions and the protocol design allows an attacker to use the server's response from one connection to answer a challenge in another. Here’s how the attack works in practice: An attacker initiates a connection to the server, posing as a legitimate user, and receives a challenge. Instead of solving it, the attacker opens a second connection to the server. In this new session, the attacker sends the server's original challenge as its own. The server helpfully encrypts it and sends the response back, which the attacker then uses to correctly answer the first connection's challenge. This bypasses authentication because the server essentially authenticates itself, granting the attacker access.
Real-world impact

Real-world CVEs caused by CWE-301

  • CVE-2005-3435

    product authentication succeeds if user-provided MD5 hash matches the hash in its database; this can be subjected to replay attacks.

How attackers exploit it

Step-by-step attacker path

  1. 1

    Identify a code path that handles untrusted input without validation.

  2. 2

    Craft a payload that exercises the unsafe behavior — injection, traversal, overflow, or logic abuse.

  3. 3

    Deliver the payload through a normal request and observe the application's reaction.

  4. 4

    Iterate until the response leaks data, executes attacker code, or escalates privileges.

Vulnerable code example

Vulnerable C

The following example demonstrates the weakness.

Vulnerable C 
unsigned char *simple_digest(char *alg,char *buf,unsigned int len, int *olen) {
  	const EVP_MD *m;
  	EVP_MD_CTX ctx;
  	unsigned char *ret;
  	OpenSSL_add_all_digests();
  	if (!(m = EVP_get_digestbyname(alg))) return NULL;
  	if (!(ret = (unsigned char*)malloc(EVP_MAX_MD_SIZE))) return NULL;
  	EVP_DigestInit(&ctx, m);
  	EVP_DigestUpdate(&ctx,buf,len);
  	EVP_DigestFinal(&ctx,ret,olen);
  	return ret;
  }
  unsigned char *generate_password_and_cmd(char *password_and_cmd) {
  	simple_digest("sha1",password,strlen(password_and_cmd)
  	...
  	);
  }
Secure code example

Secure pseudo

Secure pseudo 
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
  const safe = validateAndEscape(input);
  return executeWithGuards(safe);
}
What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Prevention checklist

How to prevent CWE-301

  • Architecture and Design Use different keys for the initiator and responder or of a different type of challenge for the initiator and responder.
  • Architecture and Design Let the initiator prove its identity before proceeding.
Detection signals

How to detect CWE-301

SAST High

Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.

DAST Moderate

Run dynamic application security testing against the live endpoint.

Runtime Moderate

Watch runtime logs for unusual exception traces, malformed input, or authorization bypass attempts.

Code review Moderate

Code review: flag any new code that handles input from this surface without using the validated framework helpers.

Plexicus auto-fix

Plexicus auto-detects CWE-301 and opens a fix PR in under 60 seconds.

Codex Remedium scans every commit, identifies this exact weakness, and ships a reviewer-ready pull request with the patch. No tickets. No hand-offs.

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Frequently asked questions

Frequently asked questions

What is CWE-301?

A reflection attack is a flaw in mutual authentication protocols that allows an attacker to impersonate a legitimate user without knowing the secret key. This happens when an attacker can bounce, or 'reflect,' a server's own challenge back to it using a second connection, tricking the system into granting access.

How serious is CWE-301?

MITRE rates the likelihood of exploit as Medium — exploitation is realistic but typically requires specific conditions.

What languages or platforms are affected by CWE-301?

MITRE has not specified affected platforms for this CWE — it can apply across most application stacks.

How can I prevent CWE-301?

Use different keys for the initiator and responder or of a different type of challenge for the initiator and responder. Let the initiator prove its identity before proceeding.

How does Plexicus detect and fix CWE-301?

Plexicus's SAST engine matches the data-flow signature for CWE-301 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.

Where can I learn more about CWE-301?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/301.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-301

CWE-1390 Parent

Weak Authentication

This vulnerability occurs when a system's login or identity verification process is too easy to bypass or fool. While it attempts to check…

CWE-1391 Sibling

Use of Weak Credentials

This vulnerability occurs when a system relies on weak authentication credentials—like default passwords, hard-coded keys, or easily…

CWE-262 Sibling

Not Using Password Aging

This vulnerability occurs when a system lacks password expiration policies, allowing users to keep the same password indefinitely.

CWE-263 Sibling

Password Aging with Long Expiration

The system enforces password changes, but the time allowed between changes is excessively long, weakening security.

CWE-289 Sibling

Authentication Bypass by Alternate Name

This vulnerability occurs when a system checks access based on a resource or user name, but fails to account for all the different names…

CWE-290 Sibling

Authentication Bypass by Spoofing

This weakness occurs when an application's authentication system can be tricked into accepting forged or manipulated credentials, allowing…

CWE-294 Sibling

Authentication Bypass by Capture-replay

This vulnerability occurs when an attacker can intercept and record legitimate authentication traffic, then replay it later to gain…

CWE-302 Sibling

Authentication Bypass by Assumed-Immutable Data

This vulnerability occurs when an authentication system incorrectly treats certain data as unchangeable, when in fact an attacker can…

CWE-303 Sibling

Incorrect Implementation of Authentication Algorithm

This weakness occurs when a developer implements a standard authentication algorithm, but makes critical mistakes in the code that cause…

Resources

Further reading

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