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CWE-123 Base Rascunho
Write-what-where Condition
A write-what-where condition occurs when an attacker can control both the data written and the exact memory location where it's written, often due to a severe memory corruption flaw like a buffer…
Definição
What is CWE-123?
A write-what-where condition occurs when an attacker can control both the data written and the exact memory location where it's written, often due to a severe memory corruption flaw like a buffer overflow.
This vulnerability is one of the most dangerous memory corruption issues. It gives an attacker near-total control over a program's execution by allowing them to overwrite critical data or code pointers in memory. Think of it as an attacker having a precise remote control to edit the program's own instruction manual while it's running, which can directly lead to arbitrary code execution.
For developers, this highlights the critical importance of secure memory management. Preventing this condition requires rigorous bounds checking, using safe functions that limit write lengths, and employing modern security features like address space layout randomization (ASLR) and stack canaries. It's often the final, exploitable result of simpler bugs like buffer overflows, making those initial flaws far more severe.
Impacto no mundo real
Real-world CVEs caused by CWE-123
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Chain: Python library does not limit the resources used to process images that specify a very large number of bands (CWE-1284), leading to excessive memory consumption (CWE-789) or an integer overflow (CWE-190).
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Chain: 3D renderer has an integer overflow (CWE-190) leading to write-what-where condition (CWE-123) using a crafted image.
Como os atacantes a exploram
Trajeto do atacante passo a passo
- 1
The classic example of a write-what-where condition occurs when the accounting information for memory allocations is overwritten in a particular fashion. Here is an example of potentially vulnerable code:
- 2
Vulnerability in this case is dependent on memory layout. The call to strcpy() can be used to write past the end of buf1, and, with a typical layout, can overwrite the accounting information that the system keeps for buf2 when it is allocated. Note that if the allocation header for buf2 can be overwritten, buf2 itself can be overwritten as well.
- 3
The allocation header will generally keep a linked list of memory "chunks". Particularly, there may be a "previous" chunk and a "next" chunk. Here, the previous chunk for buf2 will probably be buf1, and the next chunk may be null. When the free() occurs, most memory allocators will rewrite the linked list using data from buf2. Particularly, the "next" chunk for buf1 will be updated and the "previous" chunk for any subsequent chunk will be updated. The attacker can insert a memory address for the "next" chunk and a value to write into that memory address for the "previous" chunk.
- 4
This could be used to overwrite a function pointer that gets dereferenced later, replacing it with a memory address that the attacker has legitimate access to, where they have placed malicious code, resulting in arbitrary code execution.
Exemplo de código vulnerável
Vulnerable C
The classic example of a write-what-where condition occurs when the accounting information for memory allocations is overwritten in a particular fashion. Here is an example of potentially vulnerable code:
#define BUFSIZE 256
int main(int argc, char **argv) {
char *buf1 = (char *) malloc(BUFSIZE);
char *buf2 = (char *) malloc(BUFSIZE);
strcpy(buf1, argv[1]);
free(buf2);
} Exemplo de código seguro
Secure pseudo
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
const safe = validateAndEscape(input);
return executeWithGuards(safe);
} What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Lista de verificação de prevenção
How to prevent CWE-123
- Architecture and Design Use a language that provides appropriate memory abstractions.
- Operation Use OS-level preventative functionality integrated after the fact. Not a complete solution.
Sinais de deteção
How to detect CWE-123
Executar testes dinâmicos de segurança de aplicações (DAST) contra o endpoint em execução.
Monitorizar os registos em tempo de execução para traços de exceção invulgares, input malformado ou tentativas de contornar a autorização.
Revisão de código: sinalizar qualquer novo código que trate input desta superfície sem usar os ajudantes validados do framework.
CWE-123
Don't catalog this weakness. Prove it's reachable.
Plexicus turns CWE catalogs into evidence: every CWE-pattern is matched against your real code graph, reach is proven on a sandbox clone, and verified findings ship as reviewed PRs.
Perguntas frequentes O que é o CWE-123?
Qual a gravidade do CWE-123?
Que linguagens ou plataformas são afetadas pelo CWE-123?
Como posso prevenir o CWE-123?
Como é que o Plexicus deteta e corrige o CWE-123?
Onde posso saber mais sobre o CWE-123?
Frequently asked questions
O que é o CWE-123?
A write-what-where condition occurs when an attacker can control both the data written and the exact memory location where it's written, often due to a severe memory corruption flaw like a buffer overflow.
Qual a gravidade do CWE-123?
A MITRE classifica a probabilidade de exploração como Alta — esta fraqueza é ativamente explorada em campo e deve ser priorizada para remediação.
Que linguagens ou plataformas são afetadas pelo CWE-123?
MITRE lists the following affected platforms: C, C++.
Como posso prevenir o CWE-123?
Use a language that provides appropriate memory abstractions. Use OS-level preventative functionality integrated after the fact. Not a complete solution.
Como é que o Plexicus deteta e corrige o CWE-123?
O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-123 em cada commit. Quando é encontrada uma correspondência, o nosso agente Codex Remedium abre um PR de correção com o código corrigido, testes e um resumo de uma linha para o revisor.
Onde posso saber mais sobre o CWE-123?
A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/123.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.
Fraquezas relacionadas
Weaknesses related to CWE-123
CWE-787 Pai
Out-of-bounds Write
This vulnerability occurs when software incorrectly writes data outside the boundaries of its allocated memory buffer, either beyond the…
CWE-120 Irmão
Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
This vulnerability occurs when a program copies data from one memory location to another without first verifying that the source data will…
CWE-121 Irmão
Stack-based Buffer Overflow
A stack-based buffer overflow occurs when a program writes more data to a buffer located on the call stack than it can hold, corrupting…
CWE-122 Irmão
Heap-based Buffer Overflow
A heap-based buffer overflow occurs when a program writes more data to a memory buffer allocated in the heap than it can hold, corrupting…
CWE-124 Irmão
Buffer Underwrite ('Buffer Underflow')
A buffer underwrite, also known as buffer underflow, happens when a program writes data to a memory location before the official start of…
Pronto para validar o que importa?
Pronto para validar o que importa.
O Plexicus é Proof-Driven AppSec: achados validados, compreensão contextual e remediação revisada — ancorada em evidência, escopada com você.