A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).

What CVEs are caused by CWE-121?

3,247 recorded CVEs are attributed to CWE-121, including CVE-2022-20699, CVE-2022-20700, CVE-2022-20701. 18 are listed in CISA's Known Exploited Vulnerabilities (KEV) catalog.

How is CWE-121 detected?

Fuzzing: Fuzz testing (fuzzing) is a powerful technique for generating large numbers of diverse inputs - either randomly or algorithmically - and dynamically invoking the code with those inputs. Even with random inputs, it is often capable of generating unexpected results such as crashes, memory corruption, or resource consumption. Fuzzing effectively produces repeatable test cases that clearly indicate bugs, which helps developers to diagnose the issues.

What are the consequences of CWE-121?

Exploiting CWE-121 can lead to: Modify Memory, DoS: Crash, Exit, or Restart, DoS: Resource Consumption (CPU), DoS: Resource Consumption (Memory), Execute Unauthorized Code or Commands, Bypass Protection Mechanism.

Is CWE-121 actively exploited?

Yes. 18 CWE-121 vulnerabilities are in CISA's KEV catalog of actively exploited flaws, out of 3,247 recorded CVEs.

CWE-121: Stack-based Buffer Overflow (Stack Overflow)

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How to prevent it

Practical mitigations for CWE-121, grouped by where in the lifecycle they apply.

Operation

Build and Compilation

Environment Hardening

Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking.

D3-SFCV (Stack Frame Canary Validation) from D3FEND [REF-1334] discusses canary-based detection in detail.

Effectiveness: Defense in Depth

Architecture and Design

Use an abstraction library to abstract away risky APIs. Not a complete solution.

Implementation

Implement and perform bounds checking on input.

Implementation

Do not use dangerous functions such as gets. Use safer, equivalent functions which check for boundary errors.

Operation

Build and Compilation

Environment Hardening

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].

Effectiveness: Defense in Depth — These techniques do not provide a complete solution. For instance, exploits frequently use a bug that discloses memory addresses in order to maximize reliability of code execution [REF-1337]. It has also been shown that a side-channel attack can bypass ASLR [REF-1333].

Code examples

Illustrative examples from MITRE showing how the weakness appears in code.

While buffer overflow examples can be rather complex, it is possible to have very simple, yet still exploitable, stack-based buffer overflows:

Vulnerable example

#define BUFSIZE 256

The buffer size is fixed, but there is no guarantee the string in argv[1] will not exceed this size and cause an overflow.

This example takes an IP address from a user, verifies that it is well formed and then looks up the hostname and copies it into a buffer.

Vulnerable example

void host_lookup(char *user_supplied_addr){

CWE-121: Stack-based Buffer Overflow

Overview

Background

Real-world CVEs

Common consequences

How it happens

When it is introduced

Applies to

How to prevent it

How to detect it

Fuzzing

Automated Static Analysis

Automated Dynamic Analysis

Code examples

Illustrative examples

Terminology & mappings

Alternate terms

Mapped taxonomies

Frequently asked questions

References

Stay ahead of CWE-121

Overview

Background

Real-world CVEs

Common consequences

How it happens

When it is introduced

Applies to

How to prevent it

How to detect it

Fuzzing

Automated Static Analysis

Automated Dynamic Analysis

Code examples

Illustrative examples

Related weaknesses

Parent

Terminology & mappings

Alternate terms

Mapped taxonomies

Frequently asked questions

References

Stay ahead of CWE-121