CWE-124

Base Abstraction Level
Pillar — Highest-level weakness category
Class — Abstract, language-independent
Base — Specific enough to detect
Variant — Tied to specific technology
Compound — Requires multiple weaknesses Incomplete MITRE CWE Status
Stable — Fully reviewed and complete
Draft — Under development, may change
Incomplete — Partially defined by MITRE
Deprecated — No longer recommended
Obsolete — Replaced by another CWE Exploit: Medium
Buffer Underwrite ('Buffer Underflow')

Description

The product writes to a buffer using an index or pointer that references a memory location prior to the beginning of the buffer.

Top Monitored CVEs

CVE-2023-25610
CRITICAL
9.8 17.8%
2025-03-24

Consequences

Integrity, Availability — Modify Memory, DoS: Crash, Exit, or Restart

Out of bounds memory access will very likely result in the corruption of relevant memory, and perhaps instructions, possibly leading to a crash.

Integrity, Confidentiality, Availability, Access Control, Other — Execute Unauthorized Code or Commands, Modify Memory, Bypass Protection Mechanism, Other

If the corrupted memory can be effectively controlled, it may be possible to execute arbitrary code. If the corrupted memory is data rather than instructions, the system will continue to function with improper changes, possibly in violation of an implicit or explicit policy. The consequences would only be limited by how the affected data is used, such as an adjacent memory location that is used to specify whether the user has special privileges.

Access Control, Other — Bypass Protection Mechanism, Other

When the consequence is arbitrary code execution, this can often be used to subvert any other security service.

Mitigations

Phase: Requirements

Choose a language that is not susceptible to these issues.

Phase: Implementation

All calculated values that are used as index or for pointer arithmetic should be validated to ensure that they are within an expected range.

Detection

Automated Static Analysis

Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

Automated Dynamic Analysis

Use tools that are integrated during compilation to insert runtime error-checking mechanisms related to memory safety errors, such as AddressSanitizer (ASan) for C/C++ [REF-1518].