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

 
Improper Neutralization of Null Byte or NUL Character
Weakness ID: 158 (Weakness Variant)Status: Incomplete
+ Description

Description Summary

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.

+ Time of Introduction
  • Implementation
+ Applicable Platforms

Languages

All

+ Common Consequences
ScopeEffect

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 white lists 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.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness ClassWeakness Class138Improper Neutralization of Special Elements
Development Concepts (primary)699
Research Concepts (primary)1000
ChildOfCategoryCategory896SFP Cluster: Tainted Input
Software Fault Pattern (SFP) Clusters (primary)888
+ Relationship Notes

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
+ References
[REF-7] 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
Externally Mined
Modifications
Modification DateModifierOrganizationSource
2008-07-01CigitalExternal
updated Potential_Mitigations
2008-09-08MITREInternal
updated Relationships, Relationship_Notes, Taxonomy_Mappings
2008-10-14MITREInternal
updated Description
2008-11-24MITREInternal
updated Observed_Examples
2009-07-27MITREInternal
updated Potential_Mitigations
2010-02-16MITREInternal
updated Taxonomy_Mappings
2010-04-05MITREInternal
updated Description, Name
2011-03-29MITREInternal
updated Potential_Mitigations
2011-06-01MITREInternal
updated Common_Consequences
2011-06-27MITREInternal
updated Common_Consequences
2012-05-11MITREInternal
updated Observed_Examples, References, Relationships
2012-10-30MITREInternal
updated Potential_Mitigations
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
Page Last Updated: June 23, 2014