The product reads from a buffer using buffer access mechanisms such as indexes or pointers that reference memory locations after the targeted buffer.
View on MITREBy reading out-of-bounds memory, an attacker might be able to get secret values, such as memory addresses, which can bypass protection mechanisms such as ASLR in order to improve the reliability and likelihood of exploiting a separate weakness to achieve code execution instead of just denial of service.
An attacker might be able to cause a crash or other denial of service by causing the product to read a memory location that is not allowed (such as a segmentation fault), or to cause other conditions in which the read operation returns more data than is expected.
No mitigation information available for this CWE.
No detection method information available for this CWE.
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.
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).
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; }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.
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.
int main(int argc, char **argv){ char Filename[256];char Pattern[32]; /* Validate number of parameters and ensure valid content */ ... /* copy filename parameter to variable, may cause off-by-one overflow */ strncpy(Filename, argv[1], sizeof(Filename)); /* copy pattern parameter to variable, may cause off-by-one overflow */ strncpy(Pattern, argv[2], sizeof(Pattern)); printf("Searching file: %s for the pattern: %s\n", Filename, Pattern);Scan_File(Filename, Pattern);}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.
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.
/* 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';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.
View DetailsChain: product does not handle when an input string is not NULL terminated, leading to buffer over-read or heap-based buffer overflow.
View DetailsAdditional facts reviewed against primary or authoritative security sources.
Documented detection approaches include Automated Static Analysis, and Automated Dynamic Analysis; recorded impacts include Read Memory, Bypass Protection Mechanism, and DoS: Crash, Exit, or Restart; observed examples include CVE-2022-1733, CVE-2014-0160, and CVE-2009-2523. Use these source-defined anchors to turn CWE-126 into implementation, review, and verification checks for the affected component.
CWE-126: Buffer Over-read — MITRE CWEUse NIST SSDF practices to make prevention of CWE-126, Buffer Over-read, an explicit development outcome. Translate the CWE definition into security requirements and design constraints, choose safer implementation patterns and toolchain checks, and define acceptance evidence before release. Feed every confirmed occurrence back into the requirements, design review, and coding rules so the same root cause is removed across the product rather than patched in one location.
NIST SP 800-218 Secure Software Development Framework — National Institute of Standards and TechnologyUse CISA's Known Exploited Vulnerabilities catalog to test whether a vulnerability mapped to CWE-126, Buffer Over-read, has evidence of exploitation in the wild. Confirm the CVE-to-CWE root-cause mapping independently before attaching the example, then capture the affected product, required action, and remediation deadline. A missing KEV match is not evidence that the weakness is unexploited, and a KEV entry must not be generalized to every occurrence of this CWE.
Known Exploited Vulnerabilities Catalog — Cybersecurity and Infrastructure Security AgencyApply MITRE's full root-cause mapping guidance when using CWE-126, Buffer Over-read. Separate weakness language from attacker prerequisites and technical impact, check the entry's abstraction and vulnerability-mapping notes, and prefer the most specific Base or Variant supported by the evidence. Record the rejected alternatives and require an independent review before the mapping is used for remediation trends or program metrics.
CVE to CWE Root Cause Mapping Guidance — MITRE CWEApply MITRE's root-cause mapping quick tips to CWE-126, Buffer Over-read. Confirm the finding describes the causal weakness rather than an impact or attack pattern, compare the abstraction and mapping notes with plausible alternatives, and have a second reviewer challenge the selection. Preserve the evidence and reasoning so recurring defects can be measured against one consistent identifier.
CVE to CWE Root Cause Mapping Quick Tips — MITRE CWECWE-126: Buffer Over-read is a Common Weakness Enumeration (CWE) entry maintained by MITRE. The product reads from a buffer using buffer access mechanisms such as indexes or pointers that reference memory locations after the targeted buffer.
If exploited, CWE-126 (Buffer Over-read) it can compromise Confidentiality, Availability and Integrity, leading to outcomes such as Read Memory, Bypass Protection Mechanism and DoS: Crash, Exit, or Restart.
CWE-126 commonly affects C, C++ and Memory-Unsafe. Note that weaknesses are often language-agnostic patterns, so secure coding practices apply broadly.
MITRE documents real CVEs mapped to CWE-126, including CVE-2022-1733, CVE-2014-0160 and CVE-2009-2523. You can look up the full details of each CVE, including CVSS scores and remediation guidance, on our CVE Lookup tool.
A CWE (Common Weakness Enumeration) like CWE-126 describes a category of software weakness — the underlying flaw type. A CVE (Common Vulnerabilities and Exposures) identifies a specific, real-world vulnerability in a particular product. In short, a CWE is the kind of mistake, and a CVE is an instance of that mistake being found in software.