| Name |
Buffer Overflow via Symbolic Links |
|
| Likelyhood of attack |
Typical severity |
| High |
High |
|
| Summary |
This type of attack leverages the use of symbolic links to cause buffer overflows. An attacker can try to create or manipulate a symbolic link file such that its contents result in out of bounds data. When the target software processes the symbolic link file, it could potentially overflow internal buffers with insufficient bounds checking. |
| Prerequisites |
The attacker can create symbolic link on the target host. The target host does not perform correct boundary checking while consuming data from a resources. |
| Execution Flow |
| Step |
Phase |
Description |
Techniques |
| 1 |
Exploit |
The attacker creates or modifies a symbolic link pointing to a resources (e.g., file, directory). The content of the symbolic link file includes out-of-bounds (e.g. excessive length) data. |
|
| 2 |
Exploit |
The target host consumes the data pointed to by the symbolic link file. The target host may either intentionally expect to read a symbolic link or it may be fooled by the replacement of the original resource and read the attackers' symbolic link. |
|
| 3 |
Exploit |
While consuming the data, the target host does not check for buffer boundary which can lead to a buffer overflow. If the content of the data is controlled by the attacker, this is an avenue for remote code execution. |
|
|
| Solutions | Pay attention to the fact that the resource you read from can be a replaced by a Symbolic link. You can do a Symlink check before reading the file and decide that this is not a legitimate way of accessing the resource. Because Symlink can be modified by an attacker, make sure that the ones you read are located in protected directories. Pay attention to the resource pointed to by your symlink links (See attack pattern named "Forced Symlink race"), they can be replaced by malicious resources. Always check the size of the input data before copying to a buffer. Use a language or compiler that performs automatic bounds checking. Use an abstraction library to abstract away risky APIs. Not a complete solution. Compiler-based canary mechanisms such as StackGuard, ProPolice and the Microsoft Visual Studio /GS flag. Unless this provides automatic bounds checking, it is not a complete solution. Use OS-level preventative functionality. Not a complete solution. |
| Related Weaknesses |
|
CWE ID
|
Description
|
| CWE-20 |
Improper Input Validation |
| CWE-74 |
Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection') |
| CWE-118 |
Incorrect Access of Indexable Resource ('Range Error') |
| CWE-119 |
Improper Restriction of Operations within the Bounds of a Memory Buffer |
| CWE-120 |
Buffer Copy without Checking Size of Input ('Classic Buffer Overflow') |
| CWE-285 |
Improper Authorization |
| CWE-302 |
Authentication Bypass by Assumed-Immutable Data |
| CWE-680 |
Integer Overflow to Buffer Overflow |
| CWE-697 |
Incorrect Comparison |
|
| Related CAPECS |
|
CAPEC ID
|
Description
|
| CAPEC-100 |
Buffer Overflow attacks target improper or missing bounds checking on buffer operations, typically triggered by input injected by an adversary. As a consequence, an adversary is able to write past the boundaries of allocated buffer regions in memory, causing a program crash or potentially redirection of execution as per the adversaries' choice. |
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