Common Attack Pattern Enumeration and Classification
A Community Resource for Identifying and Understanding Attacks
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 queuing 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.
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.
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
Ability to deploy software on network. Ability to communicate synchronously or asynchronously with server
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.
Malicious input delivered through standard service calls, e.g. FTP or posting a message to a message queue.
Varies with instantiation of attack pattern. The main goal is so spoof or impersonate a legitimate user.
Enables attacker to impersonate another user and access commands and data (and log behavior to audit logs) on their behalf.
[R.21.1] [REF-2] G. Hoglund and G. McGraw. "Exploiting Software: How to Break Code". Addison-Wesley. February 2004.
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