Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.
CWE-46 Variant Incomplete
Path Equivalence: 'filename ' (Trailing Space)
This vulnerability occurs when an application processes file paths that end with a space character (like 'document.txt ') without properly normalizing or rejecting them. Because many operating…
Definition
What is CWE-46?
This vulnerability occurs when an application processes file paths that end with a space character (like 'document.txt ') without properly normalizing or rejecting them. Because many operating systems ignore trailing spaces in paths, this can cause the application to resolve the path differently than intended, potentially allowing attackers to access unauthorized files or directories.
At its core, this issue exploits a mismatch between how an application validates a file path and how the underlying operating system interprets it. While your code might treat 'report.pdf' and 'report.pdf ' as two distinct strings, the file system often strips the trailing space, treating them as the same location. Attackers can leverage this by crafting inputs that bypass validation checks (which look for a specific filename) but still resolve to a sensitive target file.
To prevent this, developers should implement strict path normalization that removes or rejects trailing whitespace before any security decisions are made. Always resolve user-supplied paths to their canonical, absolute form before checking permissions or performing file operations. This ensures the application's logic aligns with the operating system's actual behavior, closing this ambiguous path loophole.
Real-world impact
Real-world CVEs caused by CWE-46
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Source disclosure via trailing encoded space "%20"
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Source disclosure via trailing encoded space "%20"
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Source disclosure via trailing encoded space "%20"
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Source disclosure via trailing encoded space "%20"
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Source disclosure via trailing encoded space "%20"
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Source disclosure via trailing encoded space "%20"
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Source disclosure via trailing encoded space "%20"
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Source disclosure via trailing encoded space "%20"
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-46
- 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-46
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.
Plexicus auto-detects CWE-46 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-46?
How serious is CWE-46?
What languages or platforms are affected by CWE-46?
How can I prevent CWE-46?
How does Plexicus detect and fix CWE-46?
Where can I learn more about CWE-46?
Frequently asked questions
What is CWE-46?
This vulnerability occurs when an application processes file paths that end with a space character (like 'document.txt ') without properly normalizing or rejecting them. Because many operating systems ignore trailing spaces in paths, this can cause the application to resolve the path differently than intended, potentially allowing attackers to access unauthorized files or directories.
How serious is CWE-46?
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-46?
MITRE has not specified affected platforms for this CWE — it can apply across most application stacks.
How can I prevent CWE-46?
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-46?
Plexicus's SAST engine matches the data-flow signature for CWE-46 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-46?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/46.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-46
CWE-41 Parent
Improper Resolution of Path Equivalence
This vulnerability occurs when an application fails to properly handle different text representations that refer to the same file or…
CWE-42 Sibling
Path Equivalence: 'filename.' (Trailing Dot)
This vulnerability occurs when a system accepts file or directory paths that end with a dot (like 'file.txt.' or 'folder.') without…
CWE-44 Sibling
Path Equivalence: 'file.name' (Internal Dot)
This vulnerability occurs when an application accepts file paths containing internal dots (like 'file.ordir') without properly checking…
CWE-47 Sibling
Path Equivalence: ' filename' (Leading Space)
This vulnerability occurs when an application accepts file or directory paths that begin with a space character (like ' filename'),…
CWE-48 Sibling
Path Equivalence: 'file name' (Internal Whitespace)
This vulnerability occurs when an application accepts file paths containing internal spaces (like 'file name') without proper validation.…
CWE-49 Sibling
Path Equivalence: 'filename/' (Trailing Slash)
This vulnerability occurs when an application accepts file or directory paths that end with a slash (e.g., 'documents/') without properly…
CWE-50 Sibling
Path Equivalence: '//multiple/leading/slash'
This vulnerability occurs when an application accepts file or directory paths containing multiple leading slashes (like…
CWE-51 Sibling
Path Equivalence: '/multiple//internal/slash'
This vulnerability occurs when an application accepts file or directory paths containing multiple consecutive forward slashes (e.g.,…
CWE-52 Sibling
Path Equivalence: '/multiple/trailing/slash//'
This vulnerability occurs when an application accepts file or directory paths containing multiple consecutive forward slashes (like…
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