Reflection Attack in Authentication Protocol
Attack Pattern ID: 90 (Standard Attack Pattern Completeness: Complete)Typical Severity: HighStatus: Draft
+ Description


An attacker can abuse an authentication protocol susceptible to reflection attack in order to defeat it. Doing so allows the attacker illegitimate access to the target system, without possessing the requisite credentials.

Reflection attacks are of great concern to authentication protocols that rely on a challenge-handshake or similar mechanism. An attacker can impersonate a legitimate user and can gain illegitimate access to the system by successfully mounting a reflection attack during authentication.

Attack Execution Flow

  1. The attacker opens a connection to the target server and sends it a challenge

  2. The server responds by returning the challenge encrypted with a shared secret as well as its own challenge to the attacker

  3. Since the attacker does not possess the shared secret, he initiates a second connection to the server and sends it, as challenge, the challenge received from the server on the first connection

  4. The server treats this as just another handshake and responds by encrypting the challenge and issuing its own to the attacker

  5. The attacker now receives the encrypted challenge on the second connection and sends it as response to the server on the first connection, thereby successfully completing the handshake and authenticating to the server.

+ Attack Prerequisites

The attacker must have direct access to the target server in order to successfully mount a reflection attack. An intermediate entity, such as a router or proxy, that handles these exchanges on behalf of the attacker inhibits the attacker's ability to attack the authentication protocol.

+ Typical Likelihood of Exploit

Likelihood: High

Authentication is usually used as a means to identify and grant access to the user. If the authentication protocol can be defeated, in this instance by a reflection attack, authentication serves no purpose in identifying the legitimate users of the system from the ilegitimate ones

+ Methods of Attack
  • Protocol Manipulation
  • Spoofing
+ Examples-Instances


A single sign-on solution for a network uses a fixed pre-shared key with its clients to initiate the sign-on process in order to avoid eavesdropping on the initial exchanges.

An attacker can use a reflection attack to mimic a trusted client on the network to participate in the sign-on exchange.

+ Attacker Skills or Knowledge Required

Skill or Knowledge Level: Medium

The attacker needs to have knowledge of observing the protocol exchange and managing the required connections in order to issue and respond to challenges

+ Resources Required

All that the attacker requires is a means to observe and understand the protocol exchanges in order to reflect the challenges appropriately.

+ Solutions and Mitigations

The server must initiate the handshake by issuing the challenge. This ensures that the client has to respond before the exchange can move any further

The use of HMAC to hash the response from the server can also be used to thwart reflection. The server responds by returning its own challenge as well as hashing the client's challenge, its own challenge and the preshared secret. Requiring the client to respond with the HMAC of the two challenges ensures that only the possessor of a valid preshared secret can successfully hash in the two values.

Introducing a random nonce with each new connection ensures that the attacker can not employ two connections to attack the authentication protocol

+ Attack Motivation-Consequences
  • Privilege Escalation
  • Information Leakage
+ Related Weaknesses
CWE-IDWeakness NameWeakness Relationship Type
301Reflection Attack in an Authentication ProtocolTargeted
303Incorrect Implementation of Authentication AlgorithmSecondary
718OWASP Top Ten 2007 Category A7 - Broken Authentication and Session ManagementTargeted
+ Related Attack Patterns
NatureTypeIDNameDescriptionView(s) this relationship pertains toView\(s\)
ChildOfAttack PatternAttack Pattern114Authentication Abuse 
Mechanism of Attack (primary)1000
ChildOfAttack PatternAttack Pattern204Lifting cached, sensitive data embedded in client distributions (thick or thin) 
Mechanism of Attack (primary)1000
ChildOfAttack PatternAttack Pattern220Client-Server Protocol Manipulation 
Mechanism of Attack (primary)1000
+ Related Security Principles
  • Reluctance To Trust

  • Complete Mediation

  • Defense in Depth

+ Related Guidelines
  • Use Authentication Mechanisms, Where Appropriate, Correctly

+ Purposes
  • Penetration
  • Exploitation
+ CIA Impact
Confidentiality Impact: HighIntegrity Impact: HighAvailability Impact: Low
+ Technical Context
Architectural Paradigms
+ Content History
Chiradeep B. Chhaya2007-03-13First Draft
Sean BarnumCigital, Inc2007-04-16Review and revision of content