Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.
CWE-825 Base Incomplete
Expired Pointer Dereference
This vulnerability occurs when a program tries to use a pointer that still points to a memory location that has already been freed or released.
Definition
What is CWE-825?
This vulnerability occurs when a program tries to use a pointer that still points to a memory location that has already been freed or released.
This issue, often called a 'use-after-free' scenario, happens when your code frees a block of memory but accidentally keeps a reference (pointer) to it. Later, when that same pointer is used to read or write data, the memory may have been reallocated for a completely different purpose within your application or system. This means you're now interacting with data you didn't intend to, leading to unpredictable behavior.
The consequences depend entirely on what now occupies that memory region. You might crash the program (denial of service), read sensitive information that belongs elsewhere (information exposure), or, in the worst case, have attacker-controlled data executed as code. This makes expired pointer dereference a critical weakness that can serve as a gateway to severe security breaches.
Real-world impact
Real-world CVEs caused by CWE-825
-
access of expired memory address leads to arbitrary code execution
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stale pointer issue leads to denial of service and possibly other consequences
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Chain: a message having an unknown message type may cause a reference to uninitialized memory resulting in a null pointer dereference (CWE-476) or dangling pointer (CWE-825), possibly crashing the system or causing heap corruption.
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read of value at an offset into a structure after the offset is no longer valid
How attackers exploit it
Step-by-step attacker path
- 1
The following code shows a simple example of a use after free error:
- 2
When an error occurs, the pointer is immediately freed. However, this pointer is later incorrectly used in the logError function.
- 3
The following code shows a simple example of a double free error:
- 4
Double free vulnerabilities have two common (and sometimes overlapping) causes:
- 5
- Error conditions and other exceptional circumstances - Confusion over which part of the program is responsible for freeing the memory
Vulnerable code example
Vulnerable C
The following code shows a simple example of a use after free error:
char* ptr = (char*)malloc (SIZE);
if (err) {
abrt = 1;
free(ptr);
}
...
if (abrt) {
logError("operation aborted before commit", ptr);
} 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-825
- Architecture and Design Choose a language that provides automatic memory management.
- Implementation When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.
Detection signals
How to detect CWE-825
Run dynamic application security testing against the live endpoint.
Watch runtime logs for unusual exception traces, malformed input, or authorization bypass attempts.
Code review: flag any new code that handles input from this surface without using the validated framework helpers.
CWE-825
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.
Frequently asked questions What is CWE-825?
How serious is CWE-825?
What languages or platforms are affected by CWE-825?
How can I prevent CWE-825?
How does Plexicus detect and fix CWE-825?
Where can I learn more about CWE-825?
Frequently asked questions
What is CWE-825?
This vulnerability occurs when a program tries to use a pointer that still points to a memory location that has already been freed or released.
How serious is CWE-825?
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-825?
MITRE lists the following affected platforms: C, C++.
How can I prevent CWE-825?
Choose a language that provides automatic memory management. When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.
How does Plexicus detect and fix CWE-825?
Plexicus's SAST engine matches the data-flow signature for CWE-825 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-825?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/825.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-825
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-788 Sibling
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…
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