Führe statische Analyse (SAST) auf der Codebasis aus und suche im Datenfluss nach dem unsicheren Muster.
CWE-39 Variant Draft
Path Traversal: 'C:dirname'
This vulnerability occurs when an application accepts user input containing Windows drive letters (like 'C:dirname') without proper validation, allowing attackers to redirect file operations to…
Definition
What is CWE-39?
This vulnerability occurs when an application accepts user input containing Windows drive letters (like 'C:dirname') without proper validation, allowing attackers to redirect file operations to unintended locations or access arbitrary files on the system.
This specific path traversal variant exploits how Windows interprets file paths. When an application concatenates user-controlled input containing a drive letter (e.g., 'C:') with a base directory, it can bypass intended security boundaries. The operating system treats this as an absolute path starting from the specified drive root, potentially letting an attacker read, write, or delete sensitive files anywhere on that volume.
To prevent this, developers must rigorously validate and sanitize all user input used in file system operations. Implement strict allow-lists of permitted characters, normalize paths before checking them, and ensure the final resolved path remains within the intended safe directory (e.g., using canonicalization and then checking if the path starts with the allowed base path). Never rely solely on checking for '..' sequences, as drive letter injection provides a separate bypass method.
Auswirkungen in der Praxis
Real-world CVEs caused by CWE-39
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Remote attackers can read arbitrary files by specifying the drive letter in the requested URL.
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FTP server allows remote attackers to list arbitrary directories by using the "ls" command and including the drive letter name (e.g. C:) in the requested pathname.
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FTP server allows a remote attacker to retrieve privileged system information by specifying arbitrary paths.
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FTP server allows remote attackers to list the contents of arbitrary drives via a ls command that includes the drive letter as an argument.
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Server allows remote attackers to browse arbitrary directories via a full pathname in the arguments to certain dynamic pages.
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Remote attackers can read arbitrary files via an HTTP request whose argument is a filename of the form "C:" (Drive letter), "//absolute/path", or ".." .
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FTP server read/access arbitrary files using "C:\" filenames
Wie Angreifer es ausnutzen
Angreiferpfad Schritt für Schritt
- 1
Identifiziere einen Codepfad, der nicht vertrauenswürdige Eingaben ohne Validierung verarbeitet.
- 2
Erzeuge eine Payload, die das unsichere Verhalten auslöst — Injection, Traversal, Overflow oder Logik-Missbrauch.
- 3
Liefere die Payload über einen normalen Request aus und beobachte die Reaktion der Anwendung.
- 4
Iteriere, bis die Antwort Daten preisgibt, Angreifer-Code ausführt oder Berechtigungen eskaliert.
Verwundbares Codebeispiel
Vulnerable pseudo
MITRE hat kein Codebeispiel für diese CWE veröffentlicht. Das untenstehende Muster ist illustrativ — kanonische Referenzen findest du unter Ressourcen.
// Example pattern — see MITRE for the canonical references.
function handleRequest(input) {
// Untrusted input flows directly into the sensitive sink.
return executeUnsafe(input);
} Sicheres Codebeispiel
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.
Präventions-Checkliste
How to prevent CWE-39
- Implementation Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright. When validating filenames, use stringent allowlists that limit the character set to be used. If feasible, only allow a single "." character in the filename to avoid weaknesses such as CWE-23, and exclude directory separators such as "/" to avoid CWE-36. Use a list of allowable file extensions, which will help to avoid CWE-434. Do not rely exclusively on a filtering mechanism that removes potentially dangerous characters. This is equivalent to a denylist, which may be incomplete (CWE-184). For example, filtering "/" is insufficient protection if the filesystem also supports the use of "\" as a directory separator. Another possible error could occur when the filtering is applied in a way that still produces dangerous data (CWE-182). For example, if "../" sequences are removed from the ".../...//" string in a sequential fashion, two instances of "../" would be removed from the original string, but the remaining characters would still form the "../" string.
- 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.
Erkennungssignale
How to detect CWE-39
Führe dynamische Application-Security-Tests gegen den Live-Endpoint aus.
Beobachte Runtime-Logs auf ungewöhnliche Exception-Traces, fehlerhafte Eingaben oder Versuche, Autorisierung zu umgehen.
Code Review: Markiere jeden neuen Code, der Eingaben von dieser Oberfläche ohne validierte Framework-Helper verarbeitet.
CWE-39
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.
Häufig gestellte Fragen Was ist CWE-39?
Wie gravierend ist CWE-39?
Welche Sprachen oder Plattformen sind von CWE-39 betroffen?
Wie kann ich CWE-39 verhindern?
Wie erkennt und behebt Plexicus CWE-39?
Wo erfahre ich mehr über CWE-39?
Frequently asked questions
Was ist CWE-39?
This vulnerability occurs when an application accepts user input containing Windows drive letters (like 'C:dirname') without proper validation, allowing attackers to redirect file operations to unintended locations or access arbitrary files on the system.
Wie gravierend ist CWE-39?
MITRE hat für diese Schwachstelle keine Exploit-Wahrscheinlichkeit veröffentlicht. Behandle sie als mittlere Auswirkung, bis dein Threat Model anderes belegt.
Welche Sprachen oder Plattformen sind von CWE-39 betroffen?
MITRE hat für diese CWE keine betroffenen Plattformen spezifiziert — sie kann in den meisten Anwendungs-Stacks auftreten.
Wie kann ich CWE-39 verhindern?
Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and…
Wie erkennt und behebt Plexicus CWE-39?
Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-39 bei jedem Commit. Bei einem Treffer öffnet unser Codex-Remedium-Agent einen Fix-PR mit korrigiertem Code, Tests und einer einzeiligen Zusammenfassung für den Reviewer.
Wo erfahre ich mehr über CWE-39?
MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/39.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.
Verwandte Schwachstellen
Weaknesses related to CWE-39
CWE-36 Parent
Absolute Path Traversal
This vulnerability occurs when an application builds file paths using user input without properly blocking absolute paths like…
CWE-37 Sibling
Path Traversal: '/absolute/pathname/here'
This vulnerability occurs when an application accepts user input containing absolute file paths (starting with a forward slash like…
CWE-38 Sibling
Path Traversal: '\absolute\pathname\here'
This vulnerability occurs when an application accepts user-supplied input containing Windows-style absolute paths (like…
CWE-40 Sibling
Path Traversal: '\\UNC\share\name\' (Windows UNC Share)
This vulnerability occurs when an application accepts user input containing a Windows UNC share path (like '\\UNC\share\name') without…
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