CAPEC-10: Buffer Overflow via Environment Variables
Attack Pattern ID: 10
Abstraction: Detailed
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Description
This attack pattern involves causing a buffer overflow through manipulation of environment variables. Once the adversary finds that they can modify an environment variable, they may try to overflow associated buffers. This attack leverages implicit trust often placed in environment variables.
Extended Description
Although the focus of this attack is putting excessive content into an environment variable that is loaded into a buffer, environment variables can be used to assist a classic buffer overflow attack as well. In the case where the buffer used in a traditional buffer overflow attack is not large enough to store the adversary's shell code, they will store the shell code in an environment variable and attempt to return to its address, rather than back into the data they wrote to the buffer.
Likelihood Of Attack
High
Typical Severity
High
Relationships
This table shows the other attack patterns and high level categories that are related to this attack pattern. These relationships are defined as ChildOf and ParentOf, and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as CanFollow, PeerOf, and CanAlsoBe are defined to show similar attack patterns that the user may want to explore.
Nature
Type
ID
Name
ChildOf
Standard Attack Pattern - A standard level attack pattern in CAPEC is focused on a specific methodology or technique used in an attack. It is often seen as a singular piece of a fully executed attack. A standard attack pattern is meant to provide sufficient details to understand the specific technique and how it attempts to accomplish a desired goal. A standard level attack pattern is a specific type of a more abstract meta level attack pattern.
Detailed Attack Pattern - A detailed level attack pattern in CAPEC provides a low level of detail, typically leveraging a specific technique and targeting a specific technology, and expresses a complete execution flow. Detailed attack patterns are more specific than meta attack patterns and standard attack patterns and often require a specific protection mechanism to mitigate actual attacks. A detailed level attack pattern often will leverage a number of different standard level attack patterns chained together to accomplish a goal.
Detailed Attack Pattern - A detailed level attack pattern in CAPEC provides a low level of detail, typically leveraging a specific technique and targeting a specific technology, and expresses a complete execution flow. Detailed attack patterns are more specific than meta attack patterns and standard attack patterns and often require a specific protection mechanism to mitigate actual attacks. A detailed level attack pattern often will leverage a number of different standard level attack patterns chained together to accomplish a goal.
Standard Attack Pattern - A standard level attack pattern in CAPEC is focused on a specific methodology or technique used in an attack. It is often seen as a singular piece of a fully executed attack. A standard attack pattern is meant to provide sufficient details to understand the specific technique and how it attempts to accomplish a desired goal. A standard level attack pattern is a specific type of a more abstract meta level attack pattern.
Identify target application: The adversary identifies a target application or program to perform the buffer overflow on. In this attack the adversary looks for an application that loads the content of an environment variable into a buffer.
Experiment
Find injection vector: The adversary identifies an injection vector to deliver the excessive content to the targeted application's buffer.
Techniques
Change the values of environment variables thought to be used by the application to contain excessive data. If the program is loading the value of the environment variable into a buffer, this could cause a crash and an attack vector will be found.
Craft overflow content: The adversary crafts the content to be injected. If the intent is to simply cause the software to crash, the content need only consist of an excessive quantity of random data. If the intent is to leverage the overflow for execution of arbitrary code, the adversary crafts the payload in such a way that the overwritten return address is replaced with one of the adversary's choosing.
Techniques
Create malicious shellcode that will execute when the program execution is returned to it.
Use a NOP-sled in the overflow content to more easily "slide" into the malicious code. This is done so that the exact return address need not be correct, only in the range of all of the NOPs
Exploit
Overflow the buffer: Using the injection vector, the adversary injects the crafted overflow content into the buffer.
Prerequisites
The application uses environment variables.
An environment variable exposed to the user is vulnerable to a buffer overflow.
The vulnerable environment variable uses untrusted data.
Tainted data used in the environment variables is not properly validated. For instance boundary checking is not done before copying the input data to a buffer.
Skills Required
[Level: Low]
An attacker can simply overflow a buffer by inserting a long string into an attacker-modifiable injection vector. The result can be a DoS.
[Level: High]
Exploiting a buffer overflow to inject malicious code into the stack of a software system or even the heap can require a higher skill level.
Indicators
If the application does bound checking, it should fail when the data source is larger than the size of the destination buffer. If the application's code is well written, that failure should trigger an alert.
Consequences
This table specifies different individual consequences associated with the attack pattern. The Scope identifies the security property that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in their attack. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a pattern will be used to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.
Scope
Impact
Likelihood
Availability
Unreliable Execution
Confidentiality
Integrity
Availability
Execute Unauthorized Commands
Confidentiality
Read Data
Integrity
Modify Data
Confidentiality
Access Control
Authorization
Gain Privileges
Mitigations
Do not expose environment variable to the user.
Do not use untrusted data in your environment variables.
Use a language or compiler that performs automatic bounds checking
There are tools such as Sharefuzz [REF-2] which is an environment variable fuzzer for Unix that support loading a shared library. You can use Sharefuzz to determine if you are exposing an environment variable vulnerable to buffer overflow.
Example Instances
A buffer overflow in sccw allows local users to gain root access via the $HOME environmental variable. See also: CVE-1999-0906
A buffer overflow in the rlogin program involves its consumption of the $TERM environmental variable. See also: CVE-1999-0046
Related Weaknesses
A Related Weakness relationship associates a weakness with this attack pattern. Each association implies a weakness that must exist for a given attack to be successful. If multiple weaknesses are associated with the attack pattern, then any of the weaknesses (but not necessarily all) may be present for the attack to be successful. Each related weakness is identified by a CWE identifier.
Description
This table shows the other attack patterns and high level categories that are related to this attack pattern. These relationships are defined as ChildOf and ParentOf, and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as CanFollow, PeerOf, and CanAlsoBe are defined to show similar attack patterns that the user may want to explore.
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