CWE 649

Reliance on Obfuscation or SecurityDatabase\Encrypt\Encryption of Security-Relevant Inputs without Integrity Checking

Weakness ID: 649 (Weakness Base)

Status: Incomplete

Description

Description Summary

The software uses obfuscation or encryption of inputs that should not be mutable by an external actor, but the software does not use integrity checks to detect if those inputs have been modified.

Extended Description

When an application relies on obfuscation or incorrectly applied / weak encryption to protect client controllable tokens or parameters, that may have an effect on the user state, system state or some decision made on the server. Without protecting the tokens/parameters for integrity, the application is vulnerable to an attack where an adversary blindly traverses the space of possible values of the said token/parameter in order to attempt to gain an advantage. The goal of the attacker is to find another admissible value that will somehow elevate his or her privileges in the system, disclose information or change the behavior of the system in some way beneficial to the attacker. If the application fails to protect these critical tokens/parameters for integrity, it will not be able to determine that these values have been tampered with. Measures that are used to protect data for confidentiality should not be relied upon to provide the integrity service.

Time of Introduction

Architecture and Design
Implementation

Applicable Platforms

Languages

All

Common Consequences

Scope	Effect
Access Control	Elevation of Privilege
Confidentiality	Information Disclosure
Integrity	Functionality Abuse

Likelihood of Exploit

High

Enabling Factors for Exploitation

The application uses client controllable tokens/parameters in order to make decisions on the server side about user state, system state or other decisions related to the functionality of the application.

The application fails to protect client controllable tokens/parameters for integrity and thus not able to catch tampering.

Observed Examples

Reference	Description
CVE-2005-0039	From CVE-2005-0039: Certain configurations of IPsec, when using Encapsulating Security Payload (ESP) in tunnel mode, integrity protection at a higher layer, or Authentication Header (AH), allow remote attackers to decrypt IPSec communications by modifying the outer packet in ways that cause plaintext data from the inner packet to be returned in ICMP messages, as demonstrated using CBC bit-flipping attacks and (1) Destination Address Rewriting, (2) a modified header length that causes portions of the packet to be interpreted as IP Options, or (3) a modified protocol field and source address. The reason for the vulnerability is a failure to require integrity checking of the IPSec packet as the result of either not configuring ESP properly to support the integrity service or using AH improperly. In either case, the security gateway receiving the IPSec packet would not validate the integrity of the packet to ensure that it was not changed. Thus if the packets were intercepted the attacker could undetectably change some of the bits in the packets. The meaningful bit flipping was possible due to the known weaknesses in the CBC encryption mode. Since the attacker knew the structure of the packet, he or she was able (in one variation of the attack) to use bit flipping to change the destination IP of the packet to the destination machine controlled by the attacker. And so the destination security gateway would decrypt the packet and then forward the plaintext to the machine controlled by the attacker. The attacker could then read the original message. For instance if VPN was used with the vulnerable IPSec configuration the attacker could read the victim's e-mail. This vulnerability demonstrates the need to enforce the integrity service properly when critical data could be modified by an attacker. This problem might have also been mitigated by using an encryption mode that is not susceptible to bit flipping attacks, but the preferred mechanism to address this problem still remains message verification for integrity. While this attack focuses on the network layer and requires a man in the middle scenario, the situation is not much different at the software level where an attacker can modify tokens/parameters used by the application.

Reference

Description

CVE-2005-0039

From CVE-2005-0039: Certain configurations of IPsec, when using Encapsulating Security Payload (ESP) in tunnel mode, integrity protection at a higher layer, or Authentication Header (AH), allow remote attackers to decrypt IPSec communications by modifying the outer packet in ways that cause plaintext data from the inner packet to be returned in ICMP messages, as demonstrated using CBC bit-flipping attacks and (1) Destination Address Rewriting, (2) a modified header length that causes portions of the packet to be interpreted as IP Options, or (3) a modified protocol field and source address. The reason for the vulnerability is a failure to require integrity checking of the IPSec packet as the result of either not configuring ESP properly to support the integrity service or using AH improperly. In either case, the security gateway receiving the IPSec packet would not validate the integrity of the packet to ensure that it was not changed. Thus if the packets were intercepted the attacker could undetectably change some of the bits in the packets. The meaningful bit flipping was possible due to the known weaknesses in the CBC encryption mode. Since the attacker knew the structure of the packet, he or she was able (in one variation of the attack) to use bit flipping to change the destination IP of the packet to the destination machine controlled by the attacker. And so the destination security gateway would decrypt the packet and then forward the plaintext to the machine controlled by the attacker. The attacker could then read the original message. For instance if VPN was used with the vulnerable IPSec configuration the attacker could read the victim's e-mail. This vulnerability demonstrates the need to enforce the integrity service properly when critical data could be modified by an attacker. This problem might have also been mitigated by using an encryption mode that is not susceptible to bit flipping attacks, but the preferred mechanism to address this problem still remains message verification for integrity. While this attack focuses on the network layer and requires a man in the middle scenario, the situation is not much different at the software level where an attacker can modify tokens/parameters used by the application.

Potential Mitigations

Protect important client controllable tokens/parameters for integrity using PKI methods (i.e. digital signatures) or other means, and checks for integrity on the server side.

Repeated requests from a particular user that include invalid values of tokens/parameters (those that should not be changed manually by users) should result in the user account lockout.

Client side tokens/parameters should not be such that it would be easy/predictable to guess another valid state

Obfuscation should not be relied upon. If encryption is used, it needs to be properly applied (i.e. proven algorithm and implementation, use padding, use random initialization vector, user proper encryption mode). Even with proper encryption where the ciphertext does not leak information about the plaintext or reveal its structure compromising integrity is possible (although less likely) without the provision of the integrity service.

Relationships

Nature	Type	ID	Name	View(s) this relationship pertains to
ChildOf	Weakness Class	345	Insufficient Verification of Data Authenticity	Development Concepts (primary)699 Research Concepts (primary)1000

Content History

Submissions
Submission Date	Submitter	Organization	Source
2008-01-30	Evgeny Lebanidze	Cigital	External Submission
2008-01-30
Modifications
Modification Date	Modifier	Organization	Source
2008-09-08	CWE Content Team	MITRE	Internal
2008-09-08	updated Common Consequences, Relationships, Observed Example
2008-10-14	CWE Content Team	MITRE	Internal
2008-10-14	updated Description
2009-10-29	CWE Content Team	MITRE	Internal
2009-10-29	updated Common Consequences
Previous Entry Names
Change Date	Previous Entry Name
2008-04-11	Relying on Obfuscation or SecurityDatabase\Encrypt\Encryption with no Integrity Checking to Protect User Controllable Parameters that are Used to Determine User or System State

CWE 649

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