CAPEC-24: Filter Failure through Buffer Overflow
CAPEC版本: 3.9
更新日期: 2023-01-24
攻击模式描述
In this attack, the idea is to cause an active filter to fail by causing an oversized transaction. An attacker may try to feed overly long input strings to the program in an attempt to overwhelm the filter (by causing a buffer overflow) and hoping that the filter does not fail securely (i.e. the user input is let into the system unfiltered).
执行流程
步骤 1 Explore
[Survey] The attacker surveys the target application, possibly as a valid and authenticated user
- Spidering web sites for inputs that involve potential filtering
- Brute force guessing of filtered inputs
步骤 2 Experiment
[Attempt injections] Try to feed overly long data to the system. This can be done manually or a dynamic tool (black box) can be used to automate this. An attacker can also use a custom script for that purpose.
- Brute force attack through black box penetration test tool.
- Fuzzing of communications protocols
- Manual testing of possible inputs with attack data.
步骤 3 Experiment
[Monitor responses] Watch for any indication of failure occurring. Carefully watch to see what happened when filter failure occurred. Did the data get in?
- Boron tagging. Choose clear attack inputs that are easy to notice in output. In binary this is often 0xa5a5a5a5 (alternating 1s and 0s). Another obvious tag value is all zeroes, but it is not always obvious what goes wrong if the null values get into the data.
- Check Log files. An attacker with access to log files can look at the outcome of bad input.
步骤 4 Exploit
[Abuse the system through filter failure] An attacker writes a script to consistently induce the filter failure.
- DoS through filter failure. The attacker causes the system to crash or stay down because of its failure to filter properly.
- Malicious code execution. An attacker introduces a malicious payload and executes arbitrary code on the target system.
- An attacker can use the filter failure to introduce malicious data into the system and leverage a subsequent SQL injection, Cross Site Scripting, Command Injection or similar weakness if it exists.
前提条件
- Ability to control the length of data passed to an active filter.
所需技能
后果影响
影响范围: Integrity
技术影响: Modify Data
影响范围: Confidentiality Integrity Availability
技术影响: Execute Unauthorized Commands
说明: Run Arbitrary Code
影响范围: Confidentiality Access Control Authorization
技术影响: Bypass Protection Mechanism
影响范围: Availability
技术影响: Unreliable Execution
缓解措施
Make sure that ANY failure occurring in the filtering or input validation routine is properly handled and that offending input is NOT allowed to go through. Basically make sure that the vault is closed when failure occurs.
Pre-design: Use a language or compiler that performs automatic bounds checking.
Pre-design through Build: 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.
Operational: Use OS-level preventative functionality. Not a complete solution.
Design: Use an abstraction library to abstract away risky APIs. Not a complete solution.
示例实例
A filter is used by a web application to filter out characters that may allow the input to jump from the data plane to the control plane when data is used in a SQL statement (chaining this attack with the SQL injection attack). Leveraging a buffer overflow the attacker makes the filter fail insecurely and the tainted data is permitted to enter unfiltered into the system, subsequently causing a SQL injection.
Audit Truncation and Filters with Buffer Overflow. Sometimes very large transactions can be used to destroy a log file or cause partial logging failures. In this kind of attack, log processing code might be examining a transaction in real-time processing, but the oversized transaction causes a logic branch or an exception of some kind that is trapped. In other words, the transaction is still executed, but the logging or filtering mechanism still fails. This has two consequences, the first being that you can run transactions that are not logged in any way (or perhaps the log entry is completely corrupted). The second consequence is that you might slip through an active filter that otherwise would stop your attack.