CWE-126 Variante Brouillon

Buffer Over-read

This vulnerability occurs when a program reads data from a memory buffer using an index or pointer that points beyond the buffer's allocated boundary, accessing unintended memory locations.

Définition

What is CWE-126?

This vulnerability occurs when a program reads data from a memory buffer using an index or pointer that points beyond the buffer's allocated boundary, accessing unintended memory locations.
Buffer over-reads happen when software fails to properly validate that a read operation stays within the bounds of a buffer. This can lead to the exposure of sensitive information stored in adjacent memory, cause crashes, or create unexpected program behavior. It's a common pitfall when using low-level languages like C/C++ with functions that don't inherently check boundaries, or when manual bounds checking logic contains errors. Detecting these flaws manually across a large codebase is challenging. While SAST tools can identify the risky patterns, Plexicus uses AI to not only find them but also generate specific, context-aware fixes—transforming a security finding into a ready-to-apply code suggestion. This automates the remediation step, helping developers secure their applications faster and more consistently.
Vulnerability Diagram CWE-126
Buffer Over-read "Hello\0" Hello\0 heap memory (secrets, ptrs) A B C D E F G H I J ... read length larger than string Length-trusting reads expose data past the real terminator.
Impact réel

Real-world CVEs caused by CWE-126

  • CVE-2022-1733

    Text editor has out-of-bounds read past end of line while indenting C code

  • CVE-2014-0160

    Chain: "Heartbleed" bug receives an inconsistent length parameter (CWE-130) enabling an out-of-bounds read (CWE-126), returning memory that could include private cryptographic keys and other sensitive data.

  • CVE-2009-2523

    Chain: product does not handle when an input string is not NULL terminated, leading to buffer over-read or heap-based buffer overflow.

Comment les attaquants l'exploitent

Parcours de l'attaquant étape par étape

  1. 1

    In the following C/C++ example the method processMessageFromSocket() will get a message from a socket, placed into a buffer, and will parse the contents of the buffer into a structure that contains the message length and the message body. A for loop is used to copy the message body into a local character string which will be passed to another method for processing.

  2. 2

    However, the message length variable (msgLength) from the structure is used as the condition for ending the for loop without validating that msgLength accurately reflects the actual length of the message body (CWE-606). If msgLength indicates a length that is longer than the size of a message body (CWE-130), then this can result in a buffer over-read by reading past the end of the buffer (CWE-126).

  3. 3

    The following C/C++ example demonstrates a buffer over-read due to a missing NULL terminator. The main method of a pattern matching utility that looks for a specific pattern within a specific file uses the string strncopy() method to copy the command line user input file name and pattern to the Filename and Pattern character arrays respectively.

  4. 4

    However, the code do not take into account that strncpy() will not add a NULL terminator when the source buffer is equal in length of longer than that provide size attribute. Therefore if a user enters a filename or pattern that are the same size as (or larger than) their respective character arrays, a NULL terminator will not be added (CWE-170) which leads to the printf() read beyond the expected end of the Filename and Pattern buffers.

  5. 5

    To fix this problem, be sure to subtract 1 from the sizeof() call to allow room for the null byte to be added.

Exemple de code vulnérable

Vulnerable C

In the following C/C++ example the method processMessageFromSocket() will get a message from a socket, placed into a buffer, and will parse the contents of the buffer into a structure that contains the message length and the message body. A for loop is used to copy the message body into a local character string which will be passed to another method for processing.

Vulnérable C 
int processMessageFromSocket(int socket) {
  		int success;
  		char buffer[BUFFER_SIZE];
  		char message[MESSAGE_SIZE];
```
// get message from socket and store into buffer* 
  		
  		
  		 *//Ignoring possibliity that buffer > BUFFER_SIZE* 
  		if (getMessage(socket, buffer, BUFFER_SIZE) > 0) {
  		```
```
// place contents of the buffer into message structure* 
  				ExMessage *msg = recastBuffer(buffer);
  				
  				
  				 *// copy message body into string for processing* 
  				int index;
  				for (index = 0; index < msg->msgLength; index++) {
  				```
  					message[index] = msg->msgBody[index];
  				}
  				message[index] = '\0';
```
// process message* 
  				success = processMessage(message);}
  		return success;}
Exemple de code sécurisé

Secure C

To fix this problem, be sure to subtract 1 from the sizeof() call to allow room for the null byte to be added.

Sécurisé C 
```
/* copy filename parameter to variable, no off-by-one overflow */* 
  strncpy(Filename, argv[2], sizeof(Filename)-1);
  Filename[255]='\0';
  
  
   */* copy pattern parameter to variable, no off-by-one overflow */* 
  strncpy(Pattern, argv[3], sizeof(Pattern)-1);Pattern[31]='\0';
What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Liste de contrôle de prévention

How to prevent CWE-126

  • Architecture Use safe-by-default frameworks and APIs that prevent the unsafe pattern from being expressible.
  • Implementation Validate input at trust boundaries; use allowlists, not denylists.
  • Implementation Apply the principle of least privilege to credentials, file paths, and runtime permissions.
  • Testing Cover this weakness in CI: SAST rules + targeted unit tests for the data flow.
  • Operation Monitor logs for the runtime signals listed in the next section.
Signaux de détection

How to detect CWE-126

Automated Static Analysis High

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.)

Correction automatique Plexicus

Plexicus détecte automatiquement CWE-126 et ouvre une PR de correction en moins de 60 secondes.

Codex Remedium analyse chaque commit, identifie cette faiblesse précise et livre une pull request prête à être relue avec le correctif. Pas de tickets. Pas de transferts.

Obtenir une démo Essayer Plexicus gratuitement
Questions fréquentes

Frequently asked questions

Qu'est-ce que CWE-126 ?

This vulnerability occurs when a program reads data from a memory buffer using an index or pointer that points beyond the buffer's allocated boundary, accessing unintended memory locations.

Quelle est la gravité de CWE-126 ?

MITRE n'a pas publié de note de probabilité d'exploitation pour cette faiblesse. Traitez-la comme un impact moyen jusqu'à ce que votre modèle de menace prouve le contraire.

Quels langages ou plateformes sont affectés par CWE-126 ?

MITRE lists the following affected platforms: C, C++.

Comment puis-je prévenir CWE-126 ?

Use safe-by-default frameworks, validate untrusted input at trust boundaries, and apply the principle of least privilege. Cover the data-flow signature in CI with SAST.

Comment Plexicus détecte et corrige CWE-126 ?

Le moteur SAST de Plexicus reconnaît la signature de flux de données de CWE-126 à chaque commit. Lorsqu'une correspondance est trouvée, notre agent Codex Remedium ouvre une PR de correction avec le code corrigé, les tests et un résumé d'une ligne pour le relecteur.

Où puis-je en savoir plus sur CWE-126 ?

MITRE publie la définition canonique à https://cwe.mitre.org/data/definitions/126.html. Vous pouvez également consulter la documentation OWASP et NIST pour des conseils adjacents.

Faiblesses associées

Weaknesses related to CWE-126

CWE-788 Parent

Access of Memory Location After End of Buffer

This vulnerability occurs when software attempts to read from or write to a memory buffer using an index or pointer that points past the…

CWE-121 Frère

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 Frère

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…

Ressources

Further reading

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