CWE-73
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Nom: External Control of File Name or Path
Description du CWE
This could allow an attacker to access or modify system files or other files that are critical to the application.
Path manipulation errors occur when the following two conditions are met:
For example, the program may give the attacker the ability to overwrite the specified file or run with a configuration controlled by the attacker.
Informations générales
Modes d'introduction
Architecture and DesignImplementation : REALIZATION: This weakness is caused during implementation of an architectural security tactic.
Plateformes applicables
Langue
Class: Not Language-Specific (Undetermined)Systèmes d’exploitation
Class: Unix (Often)Class: Windows (Often)
Class: macOS (Often)
Conséquences courantes
| Portée | Impact | Probabilité |
|---|---|---|
| Integrity Confidentiality | Read Files or Directories, Modify Files or Directories Note: The application can operate on unexpected files. Confidentiality is violated when the targeted filename is not directly readable by the attacker. | |
| Integrity Confidentiality Availability | Modify Files or Directories, Execute Unauthorized Code or Commands Note: The application can operate on unexpected files. This may violate integrity if the filename is written to, or if the filename is for a program or other form of executable code. | |
| Availability | DoS: Crash, Exit, or Restart, DoS: Resource Consumption (Other) Note: The application can operate on unexpected files. Availability can be violated if the attacker specifies an unexpected file that the application modifies. Availability can also be affected if the attacker specifies a filename for a large file, or points to a special device or a file that does not have the format that the application expects. |
Exemples observés
| Références | Description |
|---|---|
CVE-2022-45918 | Chain: a learning management tool debugger uses external input to locate previous session logs (CWE-73) and does not properly validate the given path (CWE-20), allowing for filesystem path traversal using "../" sequences (CWE-24) |
CVE-2008-5748 | Chain: external control of values for user's desired language and theme enables path traversal. |
CVE-2008-5764 | Chain: external control of user's target language enables remote file inclusion. |
Mesures d’atténuation potentielles
Phases : Architecture and DesignWhen the set of filenames is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames, and reject all other inputs. For example, ID 1 could map to "inbox.txt" and ID 2 could map to "profile.txt". Features such as the ESAPI AccessReferenceMap provide this capability.
Phases : Architecture and Design // Operation
Run your code in a "jail" or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict all access to files within a particular directory.
Examples include the Unix chroot jail and AppArmor. In general, managed code may provide some protection.
This may not be a feasible solution, and it only limits the impact to the operating system; the rest of your application may still be subject to compromise.
Be careful to avoid CWE-243 and other weaknesses related to jails.
Phases : Architecture and Design
For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
Phases : 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.
Phases : Implementation
Use a built-in path canonicalization function (such as realpath() in C) that produces the canonical version of the pathname, which effectively removes ".." sequences and symbolic links (CWE-23, CWE-59).
Phases : Installation // Operation
Use OS-level permissions and run as a low-privileged user to limit the scope of any successful attack.
Phases : Operation // Implementation
If you are using PHP, configure your application so that it does not use register_globals. During implementation, develop your application so that it does not rely on this feature, but be wary of implementing a register_globals emulation that is subject to weaknesses such as CWE-95, CWE-621, and similar issues.
Phases : Testing
Use tools and techniques that require manual (human) analysis, such as penetration testing, threat modeling, and interactive tools that allow the tester to record and modify an active session. These may be more effective than strictly automated techniques. This is especially the case with weaknesses that are related to design and business rules.
Méthodes de détection
Automated Static Analysis
The external control or influence of filenames can often be detected using automated static analysis that models data flow within the product.
Automated static analysis might not be able to recognize when proper input validation is being performed, leading to false positives - i.e., warnings that do not have any security consequences or require any code changes.
Notes de cartographie des vulnérabilités
Justification : This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.Commentaire : Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.
Modèles d'attaque associés
| CAPEC-ID | Nom du modèle d'attaque |
|---|---|
| CAPEC-13 | Subverting Environment Variable Values The adversary directly or indirectly modifies environment variables used by or controlling the target software. The adversary's goal is to cause the target software to deviate from its expected operation in a manner that benefits the adversary. |
| CAPEC-267 | Leverage Alternate Encoding An adversary leverages the possibility to encode potentially harmful input or content used by applications such that the applications are ineffective at validating this encoding standard. |
| CAPEC-64 | Using Slashes and URL Encoding Combined to Bypass Validation Logic This attack targets the encoding of the URL combined with the encoding of the slash characters. An attacker can take advantage of the multiple ways of encoding a URL and abuse the interpretation of the URL. A URL may contain special character that need special syntax handling in order to be interpreted. Special characters are represented using a percentage character followed by two digits representing the octet code of the original character (%HEX-CODE). For instance US-ASCII space character would be represented with %20. This is often referred as escaped ending or percent-encoding. Since the server decodes the URL from the requests, it may restrict the access to some URL paths by validating and filtering out the URL requests it received. An attacker will try to craft an URL with a sequence of special characters which once interpreted by the server will be equivalent to a forbidden URL. It can be difficult to protect against this attack since the URL can contain other format of encoding such as UTF-8 encoding, Unicode-encoding, etc. |
| CAPEC-72 | URL Encoding This attack targets the encoding of the URL. An adversary can take advantage of the multiple way of encoding an URL and abuse the interpretation of the URL. |
| CAPEC-76 | Manipulating Web Input to File System Calls An attacker manipulates inputs to the target software which the target software passes to file system calls in the OS. The goal is to gain access to, and perhaps modify, areas of the file system that the target software did not intend to be accessible. |
| CAPEC-78 | Using Escaped Slashes in Alternate Encoding This attack targets the use of the backslash in alternate encoding. An adversary can provide a backslash as a leading character and causes a parser to believe that the next character is special. This is called an escape. By using that trick, the adversary tries to exploit alternate ways to encode the same character which leads to filter problems and opens avenues to attack. |
| CAPEC-79 | Using Slashes in Alternate Encoding This attack targets the encoding of the Slash characters. An adversary would try to exploit common filtering problems related to the use of the slashes characters to gain access to resources on the target host. Directory-driven systems, such as file systems and databases, typically use the slash character to indicate traversal between directories or other container components. For murky historical reasons, PCs (and, as a result, Microsoft OSs) choose to use a backslash, whereas the UNIX world typically makes use of the forward slash. The schizophrenic result is that many MS-based systems are required to understand both forms of the slash. This gives the adversary many opportunities to discover and abuse a number of common filtering problems. The goal of this pattern is to discover server software that only applies filters to one version, but not the other. |
| CAPEC-80 | Using UTF-8 Encoding to Bypass Validation Logic This attack is a specific variation on leveraging alternate encodings to bypass validation logic. This attack leverages the possibility to encode potentially harmful input in UTF-8 and submit it to applications not expecting or effective at validating this encoding standard making input filtering difficult. UTF-8 (8-bit UCS/Unicode Transformation Format) is a variable-length character encoding for Unicode. Legal UTF-8 characters are one to four bytes long. However, early version of the UTF-8 specification got some entries wrong (in some cases it permitted overlong characters). UTF-8 encoders are supposed to use the "shortest possible" encoding, but naive decoders may accept encodings that are longer than necessary. According to the RFC 3629, a particularly subtle form of this attack can be carried out against a parser which performs security-critical validity checks against the UTF-8 encoded form of its input, but interprets certain illegal octet sequences as characters. |
NotesNotes
CWE-114 is a Class, but it is listed a child of CWE-73 in view 1000. This suggests some abstraction problems that should be resolved in future versions.The external control of filenames can be the primary link in chains with other file-related weaknesses, as seen in the CanPrecede relationships. This is because software systems use files for many different purposes: to execute programs, load code libraries, to store application data, to store configuration settings, record temporary data, act as signals or semaphores to other processes, etc.
However, those weaknesses do not always require external control. For example, link-following weaknesses (CWE-59) often involve pathnames that are not controllable by the attacker at all.
The external control can be resultant from other issues. For example, in PHP applications, the register_globals setting can allow an attacker to modify variables that the programmer thought were immutable, enabling file inclusion (CWE-98) and path traversal (CWE-22). Operating with excessive privileges (CWE-250) might allow an attacker to specify an input filename that is not directly readable by the attacker, but is accessible to the privileged program. A buffer overflow (CWE-119) might give an attacker control over nearby memory locations that are related to pathnames, but were not directly modifiable by the attacker.
Références
REF-6
Seven Pernicious Kingdoms: A Taxonomy of Software Security ErrorsKatrina Tsipenyuk, Brian Chess, Gary McGraw.
https://samate.nist.gov/SSATTM_Content/papers/Seven%20Pernicious%20Kingdoms%20-%20Taxonomy%20of%20Sw%20Security%20Errors%20-%20Tsipenyuk%20-%20Chess%20-%20McGraw.pdf
REF-45
OWASP Enterprise Security API (ESAPI) ProjectOWASP.
http://www.owasp.org/index.php/ESAPI
Soumission
| Nom | Organisation | Date | Date de publication | Version |
|---|---|---|---|---|
| 7 Pernicious Kingdoms | Draft 3 |
Modifications
| Nom | Organisation | Date | Commentaire |
|---|---|---|---|
| Eric Dalci | Cigital | updated Time_of_Introduction | |
| CWE Content Team | MITRE | updated Relationships, Other_Notes, Taxonomy_Mappings, Weakness_Ordinalities | |
| CWE Content Team | MITRE | updated Applicable_Platforms, Causal_Nature, Common_Consequences, Demonstrative_Examples, Description, Observed_Examples, Other_Notes, Potential_Mitigations, References, Relationship_Notes, Relationships, Weakness_Ordinalities | |
| CWE Content Team | MITRE | updated Potential_Mitigations, Relationships | |
| CWE Content Team | MITRE | updated Demonstrative_Examples | |
| CWE Content Team | MITRE | updated Common_Consequences, Description | |
| CWE Content Team | MITRE | updated Detection_Factors | |
| CWE Content Team | MITRE | updated Potential_Mitigations | |
| CWE Content Team | MITRE | updated Common_Consequences, Relationships, Taxonomy_Mappings | |
| CWE Content Team | MITRE | updated Relationships, Taxonomy_Mappings | |
| CWE Content Team | MITRE | updated Demonstrative_Examples, References, Related_Attack_Patterns, Relationships, Taxonomy_Mappings | |
| CWE Content Team | MITRE | updated Potential_Mitigations | |
| CWE Content Team | MITRE | updated Relationships, Taxonomy_Mappings | |
| CWE Content Team | MITRE | updated Applicable_Platforms, Likelihood_of_Exploit, Modes_of_Introduction, Relationships, Taxonomy_Mappings | |
| CWE Content Team | MITRE | updated Potential_Mitigations, References, Relationships, Time_of_Introduction, Type | |
| CWE Content Team | MITRE | updated Potential_Mitigations, Relationships | |
| CWE Content Team | MITRE | updated Maintenance_Notes, Potential_Mitigations | |
| CWE Content Team | MITRE | updated Relationships | |
| CWE Content Team | MITRE | updated Description, Detection_Factors, Potential_Mitigations | |
| CWE Content Team | MITRE | updated Potential_Mitigations, Relationships | |
| CWE Content Team | MITRE | updated Mapping_Notes | |
| CWE Content Team | MITRE | updated Observed_Examples |
