CWE

Common Weakness Enumeration

A Community-Developed List of Software Weakness Types

CWE/SANS Top 25 Most Dangerous Software Errors
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ID

CWE-158: Improper Neutralization of Null Byte or NUL Character

Weakness ID: 158
Abstraction: Variant
Structure: Simple
Status: Incomplete
Presentation Filter:
+ Description
The software receives input from an upstream component, but it does not neutralize or incorrectly neutralizes NUL characters or null bytes when they are sent to a downstream component.
+ Extended Description
As data is parsed, an injected NUL character or null byte may cause the software to believe the input is terminated earlier than it actually is, or otherwise cause the input to be misinterpreted. This could then be used to inject potentially dangerous input that occurs after the null byte or otherwise bypass validation routines and other protection mechanisms.
+ Relationships

The table(s) below shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.

+ Relevant to the view "Research Concepts" (CWE-1000)
NatureTypeIDName
ChildOfClassClass138Improper Neutralization of Special Elements
+ Relevant to the view "Development Concepts" (CWE-699)
NatureTypeIDName
ChildOfClassClass138Improper Neutralization of Special Elements
+ Modes Of Introduction

The different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the software life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.

PhaseNote
Implementation
+ Applicable Platforms
The listings below show possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.

Languages

(Language-Independent classes): (Undetermined Prevalence)

+ Common Consequences

The table below specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.

ScopeImpactLikelihood
Integrity

Technical Impact: Unexpected State

+ Observed Examples
ReferenceDescription
Source code disclosure using trailing null.
Source code disclosure using trailing null.
Trailing null allows file include.
Null character in MIME header allows detection bypass.
Web server allows remote attackers to view the source code for CGI programs via a null character (%00) at the end of a URL.
Web server earlier allows allows remote attackers to bypass access restrictions, list directory contents, and read source code by inserting a null character (%00) in the URL.
Logging system allows an attacker to cause a denial of service (hang) by causing null bytes to be placed in log messages.
Web server allows source code for executable programs to be read via a null character (%00) at the end of a request.
Protection mechanism for limiting file access can be bypassed using a null character (%00) at the end of the directory name.
Application server allows remote attackers to read JSP source code via an encoded null byte in an HTTP GET request, which causes the server to send the .JSP file unparsed.
XSS protection mechanism only checks for sequences with an alphabetical character following a (<), so a non-alphabetical or null character (%00) following a < may be processed.
Decoding function in proxy allows regular expression bypass in ACLs via URLs with null characters.
Null byte bypasses PHP regexp check (interaction error).
Null byte bypasses PHP regexp check (interaction error).
+ Potential Mitigations
Developers should anticipate that null characters or null bytes will be injected/removed/manipulated in the input vectors of their software system. Use an appropriate combination of black lists and whitelists to ensure only valid, expected and appropriate input is processed by the system.

Phase: Implementation

Strategy: Input Validation

Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a whitelist 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 (i.e., do not rely on a blacklist). A blacklist 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, blacklists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.

Phase: Implementation

Strategy: Input Validation

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 whitelist validation schemes by introducing dangerous inputs after they have been checked.
+ Memberships
This MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. This information is often useful in understanding where a weakness fits within the context of external information sources.
NatureTypeIDName
MemberOfCategoryCategory990SFP Secondary Cluster: Tainted Input to Command
+ Notes

Relationship

This can be a factor in multiple interpretation errors, other interaction errors, filename equivalence, etc.
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERNull Character / Null Byte
WASC28Null Byte Injection
Software Fault PatternsSFP24Tainted input to command
+ References
[REF-62] Mark Dowd, John McDonald and Justin Schuh. "The Art of Software Security Assessment". Chapter 8, "NUL Character Injection", Page 411.. 1st Edition. Addison Wesley. 2006.
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVER
Modifications
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigital
updated Potential_Mitigations
2008-09-08CWE Content TeamMITRE
updated Relationships, Relationship_Notes, Taxonomy_Mappings
2008-10-14CWE Content TeamMITRE
updated Description
2008-11-24CWE Content TeamMITRE
updated Observed_Examples
2009-07-27CWE Content TeamMITRE
updated Potential_Mitigations
2010-02-16CWE Content TeamMITRE
updated Taxonomy_Mappings
2010-04-05CWE Content TeamMITRE
updated Description, Name
2011-03-29CWE Content TeamMITRE
updated Potential_Mitigations
2011-06-01CWE Content TeamMITRE
updated Common_Consequences
2011-06-27CWE Content TeamMITRE
updated Common_Consequences
2012-05-11CWE Content TeamMITRE
updated Observed_Examples, References, Relationships
2012-10-30CWE Content TeamMITRE
updated Potential_Mitigations
2014-07-30CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2017-05-03CWE Content TeamMITRE
updated Potential_Mitigations
2017-11-08CWE Content TeamMITRE
updated Applicable_Platforms
Previous Entry Names
Change DatePrevious Entry Name
2008-01-30Null Character / Null Byte
2008-04-11Failure to Remove Null Character / Null Byte
2010-04-05Failure to Sanitize Null Byte or NUL Character

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Page Last Updated: November 14, 2017