Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.
CWE-781 Variant Draft
Improper Address Validation in IOCTL with METHOD_NEITHER I/O Control Code
This vulnerability occurs when a Windows driver defines an IOCTL using METHOD_NEITHER but fails to properly check the user-supplied memory addresses before using them.
Definition
What is CWE-781?
This vulnerability occurs when a Windows driver defines an IOCTL using METHOD_NEITHER but fails to properly check the user-supplied memory addresses before using them.
When a driver uses METHOD_NEITHER for an IOCTL, it receives raw pointers directly from user mode. The driver code itself becomes fully responsible for validating that these addresses are safe and accessible before any read or write operation. Skipping this validation is dangerous because the driver will blindly trust user-controlled pointers.
Attackers can exploit this by passing crafted or invalid memory addresses, which can lead to reading sensitive kernel data, corrupting system memory, or crashing the system. Proper validation includes checks for user-mode address ranges, probe operations, and using structured methods like ProbeForRead or ProbeForWrite to prevent privilege escalation and denial-of-service attacks.
Real-world impact
Real-world CVEs caused by CWE-781
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Driver for file-sharing and messaging protocol allows attackers to execute arbitrary code.
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Anti-virus product does not validate addresses, allowing attackers to gain SYSTEM privileges.
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DVD software allows attackers to cause a crash.
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Personal firewall allows attackers to gain SYSTEM privileges.
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chain: device driver for packet-capturing software allows access to an unintended IOCTL with resultant array index error.
How attackers exploit it
Step-by-step attacker path
- 1
Identify a code path that handles untrusted input without validation.
- 2
Craft a payload that exercises the unsafe behavior — injection, traversal, overflow, or logic abuse.
- 3
Deliver the payload through a normal request and observe the application's reaction.
- 4
Iterate until the response leaks data, executes attacker code, or escalates privileges.
Vulnerable code example
Vulnerable pseudo
MITRE has not published a code example for this CWE. The pattern below is illustrative — see Resources for canonical references.
// Example pattern — see MITRE for the canonical references.
function handleRequest(input) {
// Untrusted input flows directly into the sensitive sink.
return executeUnsafe(input);
} 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-781
- Implementation If METHOD_NEITHER is required for the IOCTL, then ensure that all user-space addresses are properly validated before they are first accessed. The ProbeForRead and ProbeForWrite routines are available for this task. Also properly protect and manage the user-supplied buffers, since the I/O Manager does not do this when METHOD_NEITHER is being used. See References.
- Architecture and Design If possible, avoid using METHOD_NEITHER in the IOCTL and select methods that effectively control the buffer size, such as METHOD_BUFFERED, METHOD_IN_DIRECT, or METHOD_OUT_DIRECT.
- Architecture and Design / Implementation If the IOCTL is part of a driver that is only intended to be accessed by trusted users, then use proper access control for the associated device or device namespace. See References.
Detection signals
How to detect CWE-781
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-781
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Frequently asked questions What is CWE-781?
How serious is CWE-781?
What languages or platforms are affected by CWE-781?
How can I prevent CWE-781?
How does Plexicus detect and fix CWE-781?
Where can I learn more about CWE-781?
Frequently asked questions
What is CWE-781?
This vulnerability occurs when a Windows driver defines an IOCTL using METHOD_NEITHER but fails to properly check the user-supplied memory addresses before using them.
How serious is CWE-781?
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-781?
MITRE lists the following affected platforms: C, C++, Windows NT.
How can I prevent CWE-781?
If METHOD_NEITHER is required for the IOCTL, then ensure that all user-space addresses are properly validated before they are first accessed. The ProbeForRead and ProbeForWrite routines are available for this task. Also properly protect and manage the user-supplied buffers, since the I/O Manager does not do this when METHOD_NEITHER is being used. See References. If possible, avoid using METHOD_NEITHER in the IOCTL and select methods that effectively control the buffer size, such as…
How does Plexicus detect and fix CWE-781?
Plexicus's SAST engine matches the data-flow signature for CWE-781 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-781?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/781.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-781
CWE-1285 Parent
Improper Validation of Specified Index, Position, or Offset in Input
This vulnerability occurs when software accepts user input to determine a location—like an array index, file position, or memory…
CWE-129 Sibling
Improper Validation of Array Index
This vulnerability occurs when software uses unverified, external input to calculate or access an array index, without properly checking…
CWE-822 Can precede
Untrusted Pointer Dereference
This vulnerability occurs when software takes a value from an untrusted source, treats it as a memory address (a pointer), and then…
Resources
Further reading
- MITRE — official CWE-781 https://cwe.mitre.org/data/definitions/781.html
- Exploiting Common Flaws in Drivers http://reversemode.com/index.php?option=com_content&task=view&id=38&Itemid=1
- Remote and Local Exploitation of Network Drivers https://www.blackhat.com/presentations/bh-usa-07/Bulygin/Presentation/bh-usa-07-bulygin.pdf
- Windows driver vulnerabilities: the METHOD_NEITHER odyssey http://www.net-security.org/dl/insecure/INSECURE-Mag-18.pdf
- Buffer Descriptions for I/O Control Codes https://learn.microsoft.com/en-us/windows-hardware/drivers/kernel/buffer-descriptions-for-i-o-control-codes
- Using Neither Buffered Nor Direct I/O https://learn.microsoft.com/en-us/windows-hardware/drivers/kernel/using-neither-buffered-nor-direct-i-o
- Securing Device Objects https://learn.microsoft.com/en-us/windows-hardware/drivers/kernel/controlling-device-access
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