Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.
CWE-69 Variant Incomplete
Improper Handling of Windows ::DATA Alternate Data Stream
This vulnerability occurs when an application fails to properly secure or monitor Windows Alternate Data Streams (ADS), allowing them to be used to hide or bypass security controls.
Definition
What is CWE-69?
This vulnerability occurs when an application fails to properly secure or monitor Windows Alternate Data Streams (ADS), allowing them to be used to hide or bypass security controls.
Attackers can exploit Alternate Data Streams (ADS) to conceal malicious files or data within a file's metadata, effectively hiding it from standard system tools. For example, a file that appears normal in Windows Explorer or when listed with the `dir` command might secretly contain executable code or stolen data stored in an attached stream, evading detection based on file size or name.
Beyond hiding data, ADS can be used to circumvent access restrictions tied to the main file. If an application only validates or secures the primary data fork, an attacker might read from or write to the alternate stream to leak information or plant a backdoor, bypassing the intended security policy.
Real-world impact
Real-world CVEs caused by CWE-69
-
In IIS, remote attackers can obtain source code for ASP files by appending "::$DATA" to the URL.
-
Product does not properly record file sizes if they are stored in alternative data streams, which allows users to bypass quota restrictions.
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-69
- Testing Software tools are capable of finding ADSs on your system.
- Implementation Ensure that the source code correctly parses the filename to read or write to the correct stream.
Detection signals
How to detect CWE-69
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-69
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-69?
How serious is CWE-69?
What languages or platforms are affected by CWE-69?
How can I prevent CWE-69?
How does Plexicus detect and fix CWE-69?
Where can I learn more about CWE-69?
Frequently asked questions
What is CWE-69?
This vulnerability occurs when an application fails to properly secure or monitor Windows Alternate Data Streams (ADS), allowing them to be used to hide or bypass security controls.
How serious is CWE-69?
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-69?
MITRE lists the following affected platforms: Windows.
How can I prevent CWE-69?
Software tools are capable of finding ADSs on your system. Ensure that the source code correctly parses the filename to read or write to the correct stream.
How does Plexicus detect and fix CWE-69?
Plexicus's SAST engine matches the data-flow signature for CWE-69 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-69?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/69.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-69
CWE-66 Parent
Improper Handling of File Names that Identify Virtual Resources
This vulnerability occurs when software incorrectly processes a filename that points to a 'virtual' resource—like a device, pipe, or…
CWE-67 Sibling
Improper Handling of Windows Device Names
This vulnerability occurs when an application builds file paths from user input but fails to properly recognize or handle Windows reserved…
CWE-72 Sibling
Improper Handling of Apple HFS+ Alternate Data Stream Path
This vulnerability occurs when software fails to correctly process HFS+ file system paths that point to alternate data streams, such as a…
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