Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.
CWE-55 Variant Incomplete
Path Equivalence: '/./' (Single Dot Directory)
This vulnerability occurs when an application accepts file paths containing '/./' (single dot directory) sequences without proper validation. Attackers can exploit this to bypass intended directory…
Definition
What is CWE-55?
This vulnerability occurs when an application accepts file paths containing '/./' (single dot directory) sequences without proper validation. Attackers can exploit this to bypass intended directory structures, potentially accessing sensitive files or navigating to unauthorized locations within the file system.
The '/./' sequence, while technically valid in some filesystems, represents the current directory. When an application doesn't normalize or validate these sequences, it creates ambiguous path resolution. An attacker can inject '/./' repeatedly to manipulate how the system interprets the final path, potentially escaping restricted directories or accessing files outside the intended scope.
To prevent this, developers should implement strict path validation that resolves all dot directory sequences before processing. Use canonical path functions provided by your programming language to normalize paths, and enforce a whitelist of allowed directories. Never trust user-supplied paths directly—always validate them against a known safe base directory.
Real-world impact
Real-world CVEs caused by CWE-55
-
Server allows remote attackers to read source code for executable files by inserting a . (dot) into the URL.
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Server allows remote attackers to read password-protected files via a /./ in the HTTP request.
-
Possibly (could be a cleansing error)
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"/./////etc" cleansed to ".///etc" then "/etc"
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Server allows remote attackers to view password protected files via /./ in the URL.
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-55
- Implementation Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.
Detection signals
How to detect CWE-55
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-55
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-55?
How serious is CWE-55?
What languages or platforms are affected by CWE-55?
How can I prevent CWE-55?
How does Plexicus detect and fix CWE-55?
Where can I learn more about CWE-55?
Frequently asked questions
What is CWE-55?
This vulnerability occurs when an application accepts file paths containing '/./' (single dot directory) sequences without proper validation. Attackers can exploit this to bypass intended directory structures, potentially accessing sensitive files or navigating to unauthorized locations within the file system.
How serious is CWE-55?
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-55?
MITRE has not specified affected platforms for this CWE — it can apply across most application stacks.
How can I prevent CWE-55?
Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.
How does Plexicus detect and fix CWE-55?
Plexicus's SAST engine matches the data-flow signature for CWE-55 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-55?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/55.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-55
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-46 Sibling
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…
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.,…
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