CWE-649: Reliance on Obfuscation or Encryption of Security-Relevant Inputs without Integrity Checking
Reliance on Obfuscation or 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.
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
Phase
Description
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.
Description
