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.
CWE-788 Base Incomplete
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 buffer's allocated boundary.
Definition
What is CWE-788?
This vulnerability occurs when software attempts to read from or write to a memory buffer using an index or pointer that points past the buffer's allocated boundary.
This flaw, often called a buffer over-read or over-write, happens when a program incorrectly calculates a memory position. It typically stems from a pointer being incremented too far, an index being miscalculated, or pointer arithmetic producing an invalid address that lands outside the intended buffer's range. The result is access to adjacent memory that doesn't belong to the buffer, which can corrupt data or expose sensitive information.
For developers, this is a critical memory safety issue. It can lead to crashes, unpredictable behavior, or be exploited to leak confidential data or gain code execution. Common causes include off-by-one errors in loops, incorrect size calculations, or using untrusted input directly as an array index without proper bounds checking.
Real-world impact
Real-world CVEs caused by CWE-788
-
Classic stack-based buffer overflow in media player using a long entry in a playlist
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Heap-based buffer overflow in media player using a long entry in a playlist
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large precision value in a format string triggers overflow
-
attacker-controlled array index leads to code execution
-
OS kernel trusts userland-supplied length value, allowing reading of sensitive information
-
Chain: integer signedness error (CWE-195) passes signed comparison, leading to heap overflow (CWE-122)
How attackers exploit it
Step-by-step attacker path
- 1
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.
- 2
This function allocates a buffer of 64 bytes to store the hostname, however there is no guarantee that the hostname will not be larger than 64 bytes. If an attacker specifies an address which resolves to a very large hostname, then the function may overwrite sensitive data or even relinquish control flow to the attacker.
- 3
Note that this example also contains an unchecked return value (CWE-252) that can lead to a NULL pointer dereference (CWE-476).
- 4
In the following example, it is possible to request that memcpy move a much larger segment of memory than assumed:
- 5
If returnChunkSize() happens to encounter an error it will return -1. Notice that the return value is not checked before the memcpy operation (CWE-252), so -1 can be passed as the size argument to memcpy() (CWE-805). Because memcpy() assumes that the value is unsigned, it will be interpreted as MAXINT-1 (CWE-195), and therefore will copy far more memory than is likely available to the destination buffer (CWE-787, CWE-788).
Vulnerable code example
Vulnerable C
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.
void host_lookup(char *user_supplied_addr){
struct hostent *hp;
in_addr_t *addr;
char hostname[64];
in_addr_t inet_addr(const char *cp);
```
/*routine that ensures user_supplied_addr is in the right format for conversion */*
validate_addr_form(user_supplied_addr);
addr = inet_addr(user_supplied_addr);
hp = gethostbyaddr( addr, sizeof(struct in_addr), AF_INET);
strcpy(hostname, hp->h_name);} Secure code example
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.
Prevention checklist
How to prevent CWE-788
- 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.
Detection signals
How to detect CWE-788
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.)
Plexicus auto-detects CWE-788 and opens a fix PR in under 60 seconds.
Codex Remedium scans every commit, identifies this exact weakness, and ships a reviewer-ready pull request with the patch. No tickets. No hand-offs.
Frequently asked questions What is CWE-788?
How serious is CWE-788?
What languages or platforms are affected by CWE-788?
How can I prevent CWE-788?
How does Plexicus detect and fix CWE-788?
Where can I learn more about CWE-788?
Frequently asked questions
What is CWE-788?
This vulnerability occurs when software attempts to read from or write to a memory buffer using an index or pointer that points past the buffer's allocated boundary.
How serious is CWE-788?
MITRE has not published a likelihood-of-exploit rating for this weakness. Treat it as medium-impact until your threat model proves otherwise.
What languages or platforms are affected by CWE-788?
MITRE lists the following affected platforms: C, C++.
How can I prevent CWE-788?
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.
How does Plexicus detect and fix CWE-788?
Plexicus's SAST engine matches the data-flow signature for CWE-788 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.
Where can I learn more about CWE-788?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/788.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-788
CWE-119 Parent
Improper Restriction of Operations within the Bounds of a Memory Buffer
This vulnerability occurs when software accesses a memory buffer but reads from or writes to a location outside its allocated boundary.…
CWE-120 Sibling
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-123 Sibling
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,…
CWE-125 Sibling
Out-of-bounds Read
An out-of-bounds read occurs when software accesses memory outside the boundaries of a buffer, array, or similar data structure, reading…
CWE-130 Sibling
Improper Handling of Length Parameter Inconsistency
This vulnerability occurs when a program reads a structured data packet or message but fails to properly validate that the declared length…
CWE-466 Sibling
Return of Pointer Value Outside of Expected Range
This vulnerability occurs when a function returns a memory pointer that points outside the expected buffer range, potentially exposing…
CWE-786 Sibling
Access of Memory Location Before Start of Buffer
This vulnerability occurs when software attempts to read from or write to a memory location positioned before the official start of a…
CWE-787 Sibling
Out-of-bounds Write
This vulnerability occurs when software incorrectly writes data outside the boundaries of its allocated memory buffer, either beyond the…
CWE-805 Sibling
Buffer Access with Incorrect Length Value
This vulnerability occurs when software reads from or writes to a buffer using a loop or sequential operation, but mistakenly calculates…
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