Exploitation of Session Variables, Resource IDs and other Trusted Credentials
Attack Pattern ID: 21 (Standard Attack Pattern Completeness: Complete)Typical Severity: HighStatus: Draft
+ Description


Attacks on session IDs and resource IDs take advantage of the fact that some software accepts user input without verifying its authenticity. For example, a message queueing system that allows service requesters to post messages to its queue through an open channel (such as anonymous FTP), authorization is done through checking group or role membership contained in the posted message. However, there is no proof that the message itself, the information in the message (such group or role membership), or indeed the process that wrote the message to the queue are authentic and authorized to do so.

Many server side processes are vulnerable to these attacks because the server to server communications have not been analyzed from a security perspective or the processes "trust" other systems because they are behind a firewall. In a similar way servers that use easy to guess or spoofable schemes for representing digital identity can also be vulnerable. Such systems frequently use schemes without cryptography and digital signatures (or with broken cryptography). Session IDs may be guessed due to insufficient randomness, poor protection (passed in the clear), lack of integrity (unsigned), or improperly correlation with access control policy enforcement points.

Exposed configuration and properties files that contain system passwords, database connection strings, and such may also give an attacker an edge to identify these identifiers.

The net result is that spoofing and impersonation is possible leading to an attacker's ability to break authentication, authorization, and audit controls on the system.

Attack Execution Flow

  1. Survey the application for Indicators of Susceptibility:

    Using a variety of methods, until one is found that applies to the target system. the attacker probes for credentials, session tokens, or entry points that bypass credentials altogether.

    Attack Step Techniques

    IDAttack Step Technique DescriptionEnvironments

    Spider all available pages


    Attack known bad interfaces

    env-Web env-CommProtocol env-ClientServer env-Local


    IDtypeIndicator DescriptionEnvironments

    Session IDs are used

    env-Web env-Peer2Peer env-ClientServer env-CommProtocol

    Open access points exist that use no user IDs or passwords, but determine authorization based on message content

    env-Web env-Peer2Peer env-CommProtocol env-ClientServer env-Local


    IDtypeOutcome Description
    Session IDs are identifiable
    Open channels are available

    Security Controls

    IDtypeSecurity Control Description
    Monitor velocity of page fetching in web logs. Humans who view a page and select a link from it will click far slower and far less regularly than tools. Tools make requests very quickly and the requests are typically spaced apart regularly (e.g. 0.8 seconds between them).
    Create links on some pages that are visually hidden from web browsers. Using IFRAMES, images, or other HTML techniques, the links can be hidden from web browsing humans, but visible to spiders and programs. A request for the page, then, becomes a good predictor of an automated tool probing the application.
    Actively monitor the application and either deny or redirect requests from origins that appear to be automated.
    Monitor velocity of feature activations (non-web software). Humans who activate features (click buttons, request actions, invoke APIs, etc.) will do so far slower and far less regularly than tools. Tools make requests very quickly and the requests are typically spaced apart regularly (e.g. 0.8 seconds between them).
  1. Fetch samples:

    An attacker fetches many samples of a session ID. This may be through legitimate access (logging in, legitimate connections, etc) or just systematic probing.

    Attack Step Techniques

    IDAttack Step Technique DescriptionEnvironments

    An attacker makes many anonymous connections and records the session IDs assigned.

    env-Web env-Peer2Peer env-CommProtocol env-ClientServer

    An attacker makes authorized connections and records the session tokens or credentials issued.

    env-Web env-Peer2Peer env-CommProtocol env-ClientServer

    An attacker gains access to (legitimately or illegitimately) a nearby system (e.g., in the same operations network, DMZ, or local network) and makes a connections from it, attempting to gain the same privileges as a trusted system.

    env-Peer2Peer env-CommProtocol env-ClientServer


    IDtypeIndicator DescriptionEnvironments

    Trust in the system is based on IP address, MAC address, network locality, or other general network characteristic.

    env-CommProtocol env-ClientServer env-Peer2Peer

    Web applications use session IDs


    Network systems issue session IDs or connection IDs

    env-CommProtocol env-ClientServer env-Peer2Peer


    IDtypeOutcome Description
    Systems or applications grant trust based on logical or physical network locality.
    Session identifiers successfully spoofed
    No session IDs can be found or exploited

    Security Controls

    IDtypeSecurity Control Description
    Monitor logs for unusual amounts of invalid sessions.
    Monitor logs for unusual amounts of invalid connections or invalid requests from unauthorized hosts.
  1. Impersonate:

    An attacker can use successful experiments to impersonate an authorized user or system

    Security Controls

    IDtypeSecurity Control Description
    Analyze logs for users or systems that are connecting from unexpected sources.
    Analyze logs for users or systems successfully requesting or performing unexpected actions.
    If heuristics are sufficiently reliable, disconnect hosts or users that appear to be unauthorized impersonations.
  2. Spoofing:

    Bad data can be injected into the system by an attacker.


    IDtypeOutcome Description
    Unauthorized data is injected into an application.

    Security Controls

    IDtypeSecurity Control Description
    Apply heuristic evaluation to input data. This can include validating source addresses, user names, ACLs or other data that indicates authorization. This need not be done inline at the time the data is processed, but can be done after the processing has occurred to detect attack.
    Apply transaction-based logic to systems whose initial authorization cannot be better controlled. Roll back transactions that are subsequently determined to be fraudulent or illegitimate.
+ Attack Prerequisites

Server software must rely on weak session IDs proof and/or verification schemes

+ Typical Likelihood of Exploit

Likelihood: High

+ Methods of Attack
  • Spoofing
  • API Abuse
  • Injection
+ Examples-Instances


Thin client applications like web applications are particularly vulnerable to session ID attacks. Since the server has very little control over the client, but still must track sessions, data, and objects on the server side, cookies and other mechanisms have been used to pass the key to the session data between the client and server. When these session keys are compromised it is trivial for an attacker to impersonate a user's session in effect, have the same capabilities as the authorized user. There are two main ways for an attacker to exploit session IDs.

A brute force attack involves an attacker repeatedly attempting to query the system with a spoofed session header in the HTTP request. A web server that uses a short session ID can be easily spoofed by trying many possible combinations so the parameters session-ID= 1234 has few possible combinations, and an attacker can retry several hundred or thousand request with little to no issue on their side.

The second method is interception, where a tool such as wireshark is used to sniff the wire and pull off any unprotected session identifiers. The attacker can then use these variables and access the application.

+ Attacker Skills or Knowledge Required

Skill or Knowledge Level: Low

To achieve a direct connection with the weak or non-existent server session access control, and pose as an authorized user

+ Resources Required

Ability to deploy software on network. Ability to communicate synchronously or asynchronously with server

+ Solutions and Mitigations

Design: utilize strong federated identity such as SAML to encrypt and sign identity tokens in transit.

Implementation: Use industry standards session key generation mechanisms that utilize high amount of entropy to generate the session key. Many standard web and application servers will perform this task on your behalf.

Implementation: If the session identifier is used for authentication, such as in the so-called single sign on use cases, then ensure that it is protected at the same level of assurance as authentication tokens.

Implementation: If the web or application server supports it, then encrypting and/or signing the session ID (such as cookie) can protect the ID if intercepted.

Design: Use strong session identifiers that are protected in transit and at rest.

Implementation: Utilize a session timeout for all sessions, for example 20 minutes. If the user does not explicitly logout, the server terminates their session after this period of inactivity. If the user logs back in then a new session key is generated.

Implementation: Verify of authenticity of all session IDs at runtime.

+ Attack Motivation-Consequences
  • Privilege Escalation
  • Information Leakage
  • Data Modification
+ Injection Vector

Malicious input delivered through standard service calls, e.g. FTP or posting a message to a message queue.

+ Payload

Varies with instantiation of attack pattern. The main goal is so spoof or impersonate a legitimate user.

+ Activation Zone

Client machine and client network (e.g. Intranet)

+ Payload Activation Impact

Enables attacker to impersonate another user and access commands and data (and log behavior to audit logs) on their behalf.

+ Related Weaknesses
CWE-IDWeakness NameWeakness Relationship Type
290Authentication Bypass by SpoofingTargeted
302Authentication Bypass by Assumed-Immutable DataTargeted
346Origin Validation ErrorTargeted
539Information Leak Through Persistent CookiesSecondary
6J2EE Misconfiguration: Insufficient Session-ID LengthTargeted
384Session FixationSecondary
664Improper Control of a Resource Through its LifetimeTargeted
602Client-Side Enforcement of Server-Side SecurityTargeted
642External Control of Critical State DataTargeted
+ Related Attack Patterns
NatureTypeIDNameDescriptionView(s) this relationship pertains toView\(s\)
ChildOfCategoryCategory225Exploitation of Authentication 
Mechanism of Attack (primary)1000
PeerOfAttack PatternAttack Pattern12Choosing a Message/Channel Identifier on a Public/Multicast Channel 
Mechanism of Attack1000
ParentOfAttack PatternAttack Pattern31Accessing/Intercepting/Modifying HTTP Cookies 
Mechanism of Attack (primary)1000
ParentOfAttack PatternAttack Pattern60Reusing Session IDs (aka Session Replay) 
Mechanism of Attack (primary)1000
ParentOfAttack PatternAttack Pattern61Session Fixation 
Mechanism of Attack (primary)1000
ParentOfAttack PatternAttack Pattern62Cross Site Request Forgery (aka Session Riding) 
Mechanism of Attack (primary)1000
ParentOfAttack PatternAttack Pattern102Session Sidejacking 
Mechanism of Attack (primary)1000
ParentOfAttack PatternAttack Pattern196Session Credential Falsification through Forging 
Mechanism of Attack (primary)1000
+ Purposes
  • Penetration
+ CIA Impact
Confidentiality Impact: HighIntegrity Impact: HighAvailability Impact: Low
+ Technical Context
Architectural Paradigms
+ References
G. Hoglund and G. McGraw. "Exploiting Software: How to Break Code". Addison-Wesley. February 2004.
+ Content History
G. Hoglund and G. McGraw. Exploiting Software: How to Break Code. Addison-Wesley, February 2004.Cigital, Inc2007-01-01
Gunnar PetersonCigital, Inc2007-02-28Fleshed out content to CAPEC schema from the original descriptions in "Exploiting Software"
Sean BarnumCigital, Inc2007-03-10Review and revise
Richard StruseVOXEM, Inc2007-03-26Review and feedback leading to changes in Description
Sean BarnumCigital, Inc2007-04-13Modified pattern content according to review and feedback
Paco HopeCigital, Inc.2007-10-20Added extended Attack Execution Flow