CWE-129 Detail

CWE-129

Improper Validation of Array Index
High
Draft
2006-07-19
00h00 +00:00
2023-06-29
00h00 +00:00
Notifications for a CWE
Stay informed of any changes for a specific CWE.
Notifications manage

Name: Improper Validation of Array Index

The product uses untrusted input when calculating or using an array index, but the product does not validate or incorrectly validates the index to ensure the index references a valid position within the array.

General Informations

Modes Of Introduction

Implementation

Applicable Platforms

Language

Name: C (Often)
Name: C++ (Often)
Class: Not Language-Specific (Undetermined)

Common Consequences

Scope Impact Likelihood
Integrity
Availability
DoS: Crash, Exit, or Restart

Note: Use of an index that is outside the bounds of an array will very likely result in the corruption of relevant memory and perhaps instructions, leading to a crash, if the values are outside of the valid memory area.
IntegrityModify Memory

Note: If the memory corrupted is data, rather than instructions, the system will continue to function with improper values.
Confidentiality
Integrity
Modify Memory, Read Memory

Note: Use of an index that is outside the bounds of an array can also trigger out-of-bounds read or write operations, or operations on the wrong objects; i.e., "buffer overflows" are not always the result. This may result in the exposure or modification of sensitive data.
Integrity
Confidentiality
Availability
Execute Unauthorized Code or Commands

Note: If the memory accessible by the attacker can be effectively controlled, it may be possible to execute arbitrary code, as with a standard buffer overflow and possibly without the use of large inputs if a precise index can be controlled.
Integrity
Availability
Confidentiality
DoS: Crash, Exit, or Restart, Execute Unauthorized Code or Commands, Read Memory, Modify Memory

Note: A single fault could allow either an overflow (CWE-788) or underflow (CWE-786) of the array index. What happens next will depend on the type of operation being performed out of bounds, but can expose sensitive information, cause a system crash, or possibly lead to arbitrary code execution.

Observed Examples

References Description

CVE-2005-0369

large ID in packet used as array index

CVE-2001-1009

negative array index as argument to POP LIST command

CVE-2003-0721

Integer signedness error leads to negative array index

CVE-2004-1189

product does not properly track a count and a maximum number, which can lead to resultant array index overflow.

CVE-2007-5756

Chain: device driver for packet-capturing software allows access to an unintended IOCTL with resultant array index error.

CVE-2005-2456

Chain: array index error (CWE-129) leads to deadlock (CWE-833)

Potential Mitigations

Phases : Architecture and Design
Use an input validation framework such as Struts or the OWASP ESAPI Validation API. Note that using a framework does not automatically address all input validation problems; be mindful of weaknesses that could arise from misusing the framework itself (CWE-1173).
Phases : Architecture and Design

For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.

Even though client-side checks provide minimal benefits with respect to server-side security, they are still useful. First, they can support intrusion detection. If the server receives input that should have been rejected by the client, then it may be an indication of an attack. Second, client-side error-checking can provide helpful feedback to the user about the expectations for valid input. Third, there may be a reduction in server-side processing time for accidental input errors, although this is typically a small savings.


Phases : Requirements

Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

For example, Ada allows the programmer to constrain the values of a variable and languages such as Java and Ruby will allow the programmer to handle exceptions when an out-of-bounds index is accessed.


Phases : Operation // Build and Compilation

Run or compile the software using features or extensions that randomly arrange the positions of a program's executable and libraries in memory. Because this makes the addresses unpredictable, it can prevent an attacker from reliably jumping to exploitable code.

Examples include Address Space Layout Randomization (ASLR) [REF-58] [REF-60] and Position-Independent Executables (PIE) [REF-64]. Imported modules may be similarly realigned if their default memory addresses conflict with other modules, in a process known as "rebasing" (for Windows) and "prelinking" (for Linux) [REF-1332] using randomly generated addresses. ASLR for libraries cannot be used in conjunction with prelink since it would require relocating the libraries at run-time, defeating the whole purpose of prelinking.

For more information on these techniques see D3-SAOR (Segment Address Offset Randomization) from D3FEND [REF-1335].


Phases : Operation

Use a CPU and operating system that offers Data Execution Protection (using hardware NX or XD bits) or the equivalent techniques that simulate this feature in software, such as PaX [REF-60] [REF-61]. These techniques ensure that any instruction executed is exclusively at a memory address that is part of the code segment.

For more information on these techniques see D3-PSEP (Process Segment Execution Prevention) from D3FEND [REF-1336].


Phases : 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.

When accessing a user-controlled array index, use a stringent range of values that are within the target array. Make sure that you do not allow negative values to be used. That is, verify the minimum as well as the maximum of the range of acceptable values.


Phases : Implementation
Be especially careful to validate all input when invoking code that crosses language boundaries, such as from an interpreted language to native code. This could create an unexpected interaction between the language boundaries. Ensure that you are not violating any of the expectations of the language with which you are interfacing. For example, even though Java may not be susceptible to buffer overflows, providing a large argument in a call to native code might trigger an overflow.
Phases : Architecture and Design // Operation
Run your code using the lowest privileges that are required to accomplish the necessary tasks [REF-76]. If possible, create isolated accounts with limited privileges that are only used for a single task. That way, a successful attack will not immediately give the attacker access to the rest of the software or its environment. For example, database applications rarely need to run as the database administrator, especially in day-to-day operations.
Phases : Architecture and Design // Operation

Run the code in a "jail" or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict which files can be accessed in a particular directory or which commands can be executed by the software.

OS-level examples include the Unix chroot jail, AppArmor, and SELinux. In general, managed code may provide some protection. For example, java.io.FilePermission in the Java SecurityManager allows the software to specify restrictions on file operations.

This may not be a feasible solution, and it only limits the impact to the operating system; the rest of the application may still be subject to compromise.

Be careful to avoid CWE-243 and other weaknesses related to jails.


Detection Methods

Automated Static Analysis

This weakness can often be detected using automated static analysis tools. Many modern tools use data flow analysis or constraint-based techniques to minimize the number of false positives.

Automated static analysis generally does not account for environmental considerations when reporting out-of-bounds memory operations. This can make it difficult for users to determine which warnings should be investigated first. For example, an analysis tool might report array index errors that originate from command line arguments in a program that is not expected to run with setuid or other special privileges.


Effectiveness : High

Automated Dynamic Analysis

This weakness can be detected using dynamic tools and techniques that interact with the software using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results.

Black Box

Black box methods might not get the needed code coverage within limited time constraints, and a dynamic test might not produce any noticeable side effects even if it is successful.

Vulnerability Mapping Notes

Justification : This CWE entry is at the Variant level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Comment : Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.

Related Attack Patterns

CAPEC-ID Attack Pattern Name
CAPEC-100 Overflow Buffers
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.

NotesNotes

This weakness can precede uncontrolled memory allocation (CWE-789) in languages that automatically expand an array when an index is used that is larger than the size of the array, such as JavaScript.
An improperly validated array index might lead directly to the always-incorrect behavior of "access of array using out-of-bounds index."

References

REF-7

Writing Secure Code
Michael Howard, David LeBlanc.
https://www.microsoftpressstore.com/store/writing-secure-code-9780735617223

REF-96

Top 25 Series - Rank 14 - Improper Validation of Array Index
Jason Lam.
https://web.archive.org/web/20100316064026/http://blogs.sans.org/appsecstreetfighter/2010/03/12/top-25-series-rank-14-improper-validation-of-array-index/

REF-58

Address Space Layout Randomization in Windows Vista
Michael Howard.
https://learn.microsoft.com/en-us/archive/blogs/michael_howard/address-space-layout-randomization-in-windows-vista

REF-60

PaX
https://en.wikipedia.org/wiki/Executable_space_protection#PaX

REF-61

Understanding DEP as a mitigation technology part 1
Microsoft.
https://msrc.microsoft.com/blog/2009/06/understanding-dep-as-a-mitigation-technology-part-1/

REF-76

Least Privilege
Sean Barnum, Michael Gegick.
https://web.archive.org/web/20211209014121/https://www.cisa.gov/uscert/bsi/articles/knowledge/principles/least-privilege

REF-44

24 Deadly Sins of Software Security
Michael Howard, David LeBlanc, John Viega.

REF-64

Position Independent Executables (PIE)
Grant Murphy.
https://www.redhat.com/en/blog/position-independent-executables-pie

REF-962

Automated Source Code Security Measure (ASCSM)
Object Management Group (OMG).
http://www.omg.org/spec/ASCSM/1.0/

REF-18

The CLASP Application Security Process
Secure Software, Inc..
https://cwe.mitre.org/documents/sources/TheCLASPApplicationSecurityProcess.pdf

REF-1332

Prelink and address space randomization
John Richard Moser.
https://lwn.net/Articles/190139/

REF-1333

Jump Over ASLR: Attacking Branch Predictors to Bypass ASLR
Dmitry Evtyushkin, Dmitry Ponomarev, Nael Abu-Ghazaleh.
http://www.cs.ucr.edu/~nael/pubs/micro16.pdf

REF-1335

Segment Address Offset Randomization (D3-SAOR)
D3FEND.
https://d3fend.mitre.org/technique/d3f:SegmentAddressOffsetRandomization/

REF-1336

Process Segment Execution Prevention (D3-PSEP)
D3FEND.
https://d3fend.mitre.org/technique/d3f:ProcessSegmentExecutionPrevention/

REF-1337

Bypassing Browser Memory Protections: Setting back browser security by 10 years
Alexander Sotirov and Mark Dowd.
https://www.blackhat.com/presentations/bh-usa-08/Sotirov_Dowd/bh08-sotirov-dowd.pdf

Submission

Name Organization Date Date release Version
CLASP 2006-07-19 +00:00 2006-07-19 +00:00 Draft 3

Modifications

Name Organization Date Comment
Sean Eidemiller Cigital 2008-07-01 +00:00 added/updated demonstrative examples
CWE Content Team MITRE 2008-09-08 +00:00 updated Alternate_Terms, Applicable_Platforms, Common_Consequences, Relationships, Other_Notes, Taxonomy_Mappings, Weakness_Ordinalities
CWE Content Team MITRE 2008-11-24 +00:00 updated Relationships, Taxonomy_Mappings
CWE Content Team MITRE 2009-01-12 +00:00 updated Common_Consequences
CWE Content Team MITRE 2009-10-29 +00:00 updated Description, Name, Relationships
CWE Content Team MITRE 2009-12-28 +00:00 updated Applicable_Platforms, Common_Consequences, Observed_Examples, Other_Notes, Potential_Mitigations, Theoretical_Notes, Weakness_Ordinalities
CWE Content Team MITRE 2010-02-16 +00:00 updated Applicable_Platforms, Demonstrative_Examples, Detection_Factors, Likelihood_of_Exploit, Potential_Mitigations, References, Related_Attack_Patterns, Relationships
CWE Content Team MITRE 2010-04-05 +00:00 updated Related_Attack_Patterns
CWE Content Team MITRE 2010-06-21 +00:00 updated Common_Consequences, Potential_Mitigations, References
CWE Content Team MITRE 2010-09-27 +00:00 updated Potential_Mitigations, Relationship_Notes, Relationships
CWE Content Team MITRE 2010-12-13 +00:00 updated Demonstrative_Examples, Observed_Examples, Potential_Mitigations
CWE Content Team MITRE 2011-03-29 +00:00 updated Common_Consequences, Demonstrative_Examples, Weakness_Ordinalities
CWE Content Team MITRE 2011-06-01 +00:00 updated Common_Consequences
CWE Content Team MITRE 2011-06-27 +00:00 updated Relationships
CWE Content Team MITRE 2011-09-13 +00:00 updated Relationships, Taxonomy_Mappings
CWE Content Team MITRE 2012-05-11 +00:00 updated Demonstrative_Examples, Potential_Mitigations, References, Relationships
CWE Content Team MITRE 2012-10-30 +00:00 updated Potential_Mitigations
CWE Content Team MITRE 2014-02-18 +00:00 updated Potential_Mitigations, References
CWE Content Team MITRE 2014-07-30 +00:00 updated Relationships, Taxonomy_Mappings
CWE Content Team MITRE 2015-12-07 +00:00 updated Relationships
CWE Content Team MITRE 2017-11-08 +00:00 updated Causal_Nature, References, Relationships, Taxonomy_Mappings
CWE Content Team MITRE 2018-03-27 +00:00 updated References
CWE Content Team MITRE 2019-01-03 +00:00 updated References, Relationships, Taxonomy_Mappings
CWE Content Team MITRE 2019-09-19 +00:00 updated Potential_Mitigations
CWE Content Team MITRE 2020-02-24 +00:00 updated Potential_Mitigations, Relationships, Taxonomy_Mappings
CWE Content Team MITRE 2020-06-25 +00:00 updated Demonstrative_Examples, Potential_Mitigations, Relationships, Type
CWE Content Team MITRE 2020-08-20 +00:00 updated Potential_Mitigations, Relationships
CWE Content Team MITRE 2020-12-10 +00:00 updated Relationships
CWE Content Team MITRE 2021-03-15 +00:00 updated References, Relationships
CWE Content Team MITRE 2022-10-13 +00:00 updated References, Relationships, Taxonomy_Mappings
CWE Content Team MITRE 2023-04-27 +00:00 updated Potential_Mitigations, References, Relationships
CWE Content Team MITRE 2023-06-29 +00:00 updated Mapping_Notes