| Attack Pattern ID | Pattern Abstraction: Standard 39 |
| Typical Severity | Medium |
| Description | Summary In circumstances where an application holds important data client-side in tokens (cookies, URLs, data files, and so forth) that data can be manipulated. If client
or server-side application components reinterpret that data as authentication tokens or data (such as store item pricing or wallet information) then even opaquely manipulating
that data may bear fruit for an Attacker. In this pattern an attacker undermines the assumption that client side tokens have been adequately protected from tampering through use of encryption or obfuscation. Attack Execution Flow Explore Enumerate information passed to client side:
The attacker identifies the parameters used as part of tokens to take business or security decisions
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Attack Step Techniques |
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| Description | Environments |
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| Use WebScarab to reveal hidden fields while browsing. | env-Web | | Use a sniffer to capture packets | env-ClientServer env-Peer2Peer env-CommProtocol | | View source of web page to find hidden fields | env-Web | | Examine URL to see if any opaque tokens are in it | env-Web | | Disassemble or decompile client-side application | env-ClientServer env-Peer2Peer | | Use debugging tools such as File Monitor, Registry Monitor, Debuggers, etc. | env-ClientServer env-Peer2Peer |
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Indicators of Susceptibility
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| ID | Type | Description | Environments |
|---|
| c39s1i1 | Positive | Opaque hidden form fields in a web page | env-Web | | c39s1i2 | Positive | Opaque session tokens/tickets | env-Web env-Peer2Peer env-ClientServer env-CommProtocol | | c39s1i3 | Positive | Opaque protocol fields | env-ClientServer env-Peer2Peer env-CommProtocol | | c39s1i4 | Positive | Opaque Resource Locator | env-Web env-Peer2Peer env-ClientServer env-CommProtocol |
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Outcomes |
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| ID | Type | Description |
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| c39s1o1 | Success | At least one opaque client-side token found | | c39s1o2 | Failure | No opaque client-side tokens found |
Determine protection mechanism for opaque token:
The attacker determines the protection mechanism used to protect the confidentiality and integrity of these data tokens. They may may be obfuscated or a full blown encryption may be used.
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Attack Step Techniques |
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| Description | Environments |
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| Look for signs of well-known character encodings | env-Web env-ClientServer env-Peer2Peer env-CommProtocol | | Look for cryptographic signatures | env-Web env-ClientServer env-Peer2Peer env-CommProtocol | | Look for delimiters or other indicators of structure | env-Web env-ClientServer env-Peer2Peer env-CommProtocol |
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Indicators of Susceptibility
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| ID | Type | Description | Environments |
|---|
| c39s2i1 | Positive | Standard signatures of well-known encodings detected | env-Web env-ClientServer env-Peer2Peer env-CommProtocol | | c39s2i2 | Positive | Token or structural block’s length being multiple of well-known block size of a cryptographic algorithm | env-Web env-ClientServer env-Peer2Peer env-CommProtocol | | c39s2i3 | Positive | Clear structural boundaries or delimiters | env-Web env-ClientServer env-Peer2Peer env-CommProtocol | | c39s2i4 | Negative | Failure outcome in previous step | env-Web env-ClientServer env-Peer2Peer env-CommProtocol |
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Outcomes |
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| ID | Type | Description |
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| c39s2o1 | Success | Protection/encoding scheme identified | | c39s2o2 | Failure | No information about protection/encoding scheme could not be determined |
Experiment Modify parameter/token values: Trying each parameter in turn, the attacker modifies the values |
Attack Step Techniques |
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| Description | Environments |
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| Modify tokens logically | env-Web env-ClientServer env-Peer2Peer env-CommProtocol | | Modify tokens arithmetically | env-Web env-ClientServer env-Peer2Peer env-CommProtocol | | Modify tokens bitwise | env-Web env-ClientServer env-Peer2Peer env-CommProtocol | | Modify structural components of tokens | env-Web env-ClientServer env-Peer2Peer env-CommProtocol | | Modify order of parameters/tokens | env-Web env-ClientServer env-Peer2Peer env-CommProtocol |
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Indicators of Susceptibility
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| ID | Type | Description | Environments |
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| c39s3i1 | Positive | Success outcome in first step. | env-Web env-ClientServer env-Peer2Peer env-CommProtocol | | c39s3i2 | Negative | Failure outcome in first step | env-Web env-ClientServer env-Peer2Peer env-CommProtocol |
Cycle through values for each parameter.: Depending on the nature of the application, the attacker now cycles through values of each parameter and observes the effects of this modification in the data returned by the server |
Attack Step Techniques |
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| Description | Environments |
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| Use network-level packet injection tools such as netcat | env-Web env-ClientServer env-Peer2Peer env-CommProtocol | | Use application-level data modification tools such as Tamper Data, WebScarab, TamperIE, etc. | env-Web | | Use modified client (modified by reverse engineering) | env-ClientServer env-Peer2Peer env-CommProtocol | | Use debugging tools to modify data in client | env-ClientServer env-Peer2Peer |
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Indicators of Susceptibility
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| ID | Type | Description | Environments |
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| c39s4i1 | Positive | Success outcome in first step | env-Web env-ClientServer env-Peer2Peer env-CommProtocol | | c39s4i2 | Negative | Failure outcome in first step | env-Web env-ClientServer env-Peer2Peer env-CommProtocol |
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Outcomes |
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| ID | Type | Description |
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| c39s4o1 | Success | Subversion of security controls on server | | c39s4o2 | Failure | Client token reset by server | | c39s4o3 | Inconclusive | Detailed error message describing problem with token, received from server |
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Security Controls |
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| ID | Type | Description |
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| c39s4sc1 | Detective | Unexpected/invalid token/parameter value in application logs on server | | c39s4sc2 | Corrective | Reset session upon receipt of unexpected/invalid token/parameter value |
|
| Attack Prerequisites |
An attacker already has some access to the system or can steal the client based data tokens from another user who has access to the system.
For an Attacker to viably execute this attack, some data (later interpreted by the application) must be held client-side in a way that can be manipulated without detection. This means that the data or tokens are not CRCd as part of their value or through a separate meta-data store elsewhere. |
| Typical Likelihood of Exploit |
Very High
|
| Methods of Attack | - Modification of Resources
|
| Examples-Instances | Description With certain price watching websites, that aggregate products available prices, the user can buy items through whichever vendors has product availability, the best price, or other differentiator. Once a user selects an item, the site must broker the purchase of that item with the vendor. Because vendors sell the same product through different channel partners at different prices, token exchange between price watching sites and selling vendors will often contain pricing information. With some price watching sites, manipulating URL-data (which is encrypted) even opaquely yields different prices charged by the fulfilling vendor. If the manipulated price turns out higher, the Attacker can cancel purchase. If the Attacker succeeded in manipulating the token and creating a lower price, he/she proceeds. Description
Upon successful authentication user is granted an encrypted authentication cookie by the server and it is stored on the client. One piece of information stored in the authentication cookie reflects the access level of the user (e.g. "u" for user). The authentication cookie is encrypted using the Electronic Code Book (ECB) mode, that naively encrypts each of the plaintext blocks to each of the ciphertext blocks separately. An attacker knows the structure of the cookie and can figure out what bits (encrypted) store the information relating to the access level of the user. An attacker modifies the authentication cookie and effectively substitutes "u" for "a" by flipping some of the corresponding bits of ciphertext (trial and error). Once the correct "flip" is found, when the system is accessed, the attacker is granted administrative privileges in the system. Note that in this case an attacker did not have to figure out the exact encryption algorithm or find the secret key, but merely exploit the weakness inherent in using the ECB encryption mode.
Related Vulnerability Description
Archangel Weblog 0.90.02 allows remote attackers to bypass authentication by setting the ba_admin cookie to 1.
Related Vulnerability |
| Attacker Skill or Knowledge Required |
Medium: If the client site token is obfuscated.
High: If the client site token is encrypted.
|
| Resources Required | The Attacker needs no special hardware-based resources in order to
conduct this attack. Software plugins, such as Tamper Data for Firefox, may help in
manipulating URL- or cookie-based data.
|
| Probing Techniques |
Tamper with the client side data token and observe the effects it has on interaction with the system.
This attack is in and of itself a trial-and-error-based probing technique. |
| Solutions and Mitigations | One solution to this problem is to protect encrypted data with a CRC of some sort. If knowing who last manipulated the data is important, then using a cryptographic "message authentication code" (or hMAC) is prescribed. However, this guidance is not a panecea. In particular, any value created by (and therefore encrypted by) the client, which itself is a "malicous" value, all the protective cryptography in the world can't make the value 'correct' again. Put simply, if the client has control over the whole process of generating and encoding the value--then simply protecting its integrity doesn't help.
Make sure to protect client side authentication tokens for confidentiality (encryption) and integrity (signed hash)
Make sure that all session tokens use a good source of randomness
Perform validation on the server side to make sure that client side data tokens are consistent with what is expected.
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| Attack Motivation-Consequences | - Data Modification
- Privilege Escalation
|
| Context Description | The context in which this attack can operate is any circumstance in
which important data, stored client-side, is reinterpreted by the client itself or a
server-side component. The server-side component may or may not be the same system that
produced the data (it is not in the given example instance). But, in all cases, the data
stored is protected through some means--such as encryption. However, it's important to
stipulate that the means used to protect this data does not employ an effetive integrity
check.
|
| Related Weaknesses | | CWE-ID | Weakness Name | Weakness Relationship Type |
|---|
| 353 | Failure to Add Integrity Check Value | Targeted | | 285 | Missing or Inconsistent Access Control | Secondary | | 302 | Authentication Bypass by Assumed-Immutable Data | Targeted | | 472 | External Control of Assumed-Immutable Web Parameter | Targeted | | 565 | Use of Cookies in Security Decision | Targeted | | 315 | Plaintext Storage in a Cookie | Targeted | | 539 | Information Leak Through Persistent Cookies | Targeted | | 384 | Session Fixation | Secondary | | 233 | Parameter Problems | Secondary |
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| Related Attack Patterns | | ID | Name | Relationship Type | Relationship Description |
|---|
| 31 | Accessing/Intercepting/Modifying HTTP Cookies | More Abstract | | | 22 | Exploiting Trust in Client (aka Make the Client Invisible) | More Detailed | |
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| Relevant Security Requirements | Sensitive information stored client side must be integrity checked upon return before use |
| Related Security Principles | - Reluctance to Trust
- Never Assuming that your Secrets are Safe
- Least Privilege
- Complete Mediation
|
| Related Guidelines | - Never Use Unvalidated Input as Part of a Directive to any Internal Component
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| Purpose | Penetration Exploitation |
| CIA Impact | | Confidentiality Impact | Integrity Impact | Availability Impact |
|---|
| High | High | Low |
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| Technical Context | | Architectural Paradigm | Framework | Platform | Language |
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| All | All | All | All |
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| Source | | Submission(s) |
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| Submitter | Organization | Date | Comment |
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| John Steven | Cigital, Inc | 2007-02-10 | Initial core pattern content |
| Modification(s) |
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| Modifier | Organization | Date | Comment |
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| Chiradeep B. Chhaya | Cigital, Inc | 2007-02-23 | Fleshed out pattern with extra content | | Eugene Lebanidze | Cigital, Inc | 2007-02-27 | Added new examples and other content | | Richard Struse | VOXEM, Inc | 2007-03-26 | Review and feedback leading to changes in Solutions and Related Attack Patterns | | Sean Barnum | Cigital, Inc | 2007-04-13 | Modified pattern content according to review and feedback | | Amit Sethi | Cigital, Inc. | 2007-10-29 | Added extended Attack Execution Flow |
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