CWE-125: Out-of-bounds Read
The product reads data past the end, or before the beginning, of the intended buffer.
How it's found
Out-of-bounds Read is typically found by tracing untrusted input from where it enters the system to the point where it is used without the check or neutralization this weakness describes, combining manual code review with dynamic testing.
Vulnerable vs. safe
// check that the array index is less than the maximum
// length of the array
// if array index is invalid then output error message
// and return value indicating error
// get the value at the specified index of the arrayvalue = array[index];
printf("Value is: %d\n", array[index]);value = -1;int value;if (index < len) {}else {}return value;int getValueFromArray(int *array, int len, int index) {}// check that the array index is within the correct
// range of values for the array...if (index >= 0 && index < len) {...Consequences
- Read Memory: An attacker could get secret values such as cryptographic keys, PII, memory addresses, or other information that could be used in additional attacks.
- Bypass Protection Mechanism: Out-of-bounds memory could contain memory addresses or other information that can be used to bypass ASLR and other protection mechanisms in order to improve the reliability of exploiting a separate weakness for code execution.
- DoS: Crash, Exit, or Restart: An attacker could cause a segmentation fault or crash by causing memory to be read outside of the bounds of the buffer. This is especially likely when the code reads a variable amount of data and assumes that a sentinel exists to stop the read operation, such as a NUL in a string.
- Varies by Context: The read operation could produce other undefined or unexpected results.
Mitigations
- Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright. To reduce the likelihood of introducing an out-of-bounds read, ensure that you validate and ensure correct calculations for any length argument, buffer size calculation, or offset. Be especially careful of relying on a sentinel (i.e. special character such as NUL) in untrusted inputs.
- Architecture and Design: Use a language that provides appropriate memory abstractions.
Where this fits in a TurboPentest engagement
This weakness is not covered by the automated black-box pentest. IntegSec pentesters cover it in a manual engagement.
Frequently asked questions
What is CWE-125?
The product reads data past the end, or before the beginning, of the intended buffer.
How do you find Out-of-bounds Read?
Out-of-bounds Read is typically found by tracing untrusted input from where it enters the system to the point where it is used without the check or neutralization this weakness describes, combining manual code review with dynamic testing.
What is the impact of CWE-125?
Read Memory: An attacker could get secret values such as cryptographic keys, PII, memory addresses, or other information that could be used in additional attacks. Bypass Protection Mechanism: Out-of-bounds memory could contain memory addresses or other information that can be used to bypass ASLR and other protection mechanisms in order to improve the reliability of exploiting a separate weakness for code execution. DoS: Crash, Exit, or Restart: An attacker could cause a segmentation fault or crash by causing memory to be read outside of the bounds of the buffer. This is especially likely when the code reads a variable amount of data and assumes that a sentinel exists to stop the read operation, such as a NUL in a string. Varies by Context: The read operation could produce other undefined or unexpected results.
Does TurboPentest test for Out-of-bounds Read?
This weakness is not covered by the automated black-box pentest. IntegSec pentesters cover it in a manual engagement.
Related CWEs
Written and reviewed by
Michel Chamberland - Founder & CEO, IntegSec
CISSP, OSCP, OSCE, CEH, GIAC, CCSK · 20+ years in offensive security
Michel has spent 20+ years on offensive security teams including IBM X-Force Red and Trustwave SpiderLabs, leading penetration tests, red team engagements, and breach response for Fortune 500 customers. He is the founder of IntegSec and the architect of TurboPentest.
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