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Home > CWE List > CWE-494: Download of Code Without Integrity Check (4.18)
ID
CWE Glossary Definition

CWE-494: Download of Code Without Integrity Check

Weakness ID: 494
Vulnerability Mapping: ALLOWED This CWE ID may be used to map to real-world vulnerabilities
Abstraction: Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.
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Description
The product downloads source code or an executable from a remote location and executes the code without sufficiently verifying the origin and integrity of the code.
Extended Description
An attacker can execute malicious code by compromising the host server, performing DNS spoofing, or modifying the code in transit.
Common Consequences
Section HelpThis table 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.
Impact Details

Execute Unauthorized Code or Commands; Alter Execution Logic; Other

Scope: Integrity, Availability, Confidentiality, Other

Executing untrusted code could compromise the control flow of the program. The untrusted code could execute attacker-controlled commands, read or modify sensitive resources, or prevent the software from functioning correctly for legitimate users.
Potential Mitigations
Phase(s) Mitigation

Implementation
Perform proper forward and reverse DNS lookups to detect DNS spoofing.
Note: This is only a partial solution since it will not prevent your code from being modified on the hosting site or in transit.

Architecture and Design; Operation

Encrypt the code with a reliable encryption scheme before transmitting.

This will only be a partial solution, since it will not detect DNS spoofing and it will not prevent your code from being modified on the hosting site.

Architecture and Design

Strategy: Libraries or Frameworks

Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid [REF-1482].

Speficially, it may be helpful to use tools or frameworks to perform integrity checking on the transmitted code.

  • When providing the code that is to be downloaded, such as for automatic updates of the software, then use cryptographic signatures for the code and modify the download clients to verify the signatures. Ensure that the implementation does not contain CWE-295, CWE-320, CWE-347, and related weaknesses.
  • Use code signing technologies such as Authenticode. See references [REF-454] [REF-455] [REF-456].

Architecture and Design; Operation

Strategy: Environment Hardening

Run your code using the lowest privileges that are required to accomplish the necessary tasks [REF-76]. If possible, create isolated accounts with limited privileges that are only used for a single task. That way, a successful attack will not immediately give the attacker access to the rest of the software or its environment. For example, database applications rarely need to run as the database administrator, especially in day-to-day operations.

Architecture and Design; Operation

Strategy: Sandbox or Jail

Run the code in a "jail" or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict which files can be accessed in a particular directory or which commands can be executed by the software.

OS-level examples include the Unix chroot jail, AppArmor, and SELinux. In general, managed code may provide some protection. For example, java.io.FilePermission in the Java SecurityManager allows the software to specify restrictions on file operations.

This may not be a feasible solution, and it only limits the impact to the operating system; the rest of the application may still be subject to compromise.

Be careful to avoid CWE-243 and other weaknesses related to jails.

Effectiveness: Limited

Note: The effectiveness of this mitigation depends on the prevention capabilities of the specific sandbox or jail being used and might only help to reduce the scope of an attack, such as restricting the attacker to certain system calls or limiting the portion of the file system that can be accessed.
Relationships
Section Help This table 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" (View-1000)
Nature Type ID Name
ChildOf Class Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource. 345 Insufficient Verification of Data Authenticity
ChildOf Class Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource. 669 Incorrect Resource Transfer Between Spheres
CanFollow Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource. 79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Relevant to the view "Software Development" (View-699)
Nature Type ID Name
MemberOf Category Category - a CWE entry that contains a set of other entries that share a common characteristic. 1214 Data Integrity Issues
Relevant to the view "Weaknesses for Simplified Mapping of Published Vulnerabilities" (View-1003)
Nature Type ID Name
ChildOf Class Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource. 669 Incorrect Resource Transfer Between Spheres
Relevant to the view "Architectural Concepts" (View-1008)
Nature Type ID Name
MemberOf Category Category - a CWE entry that contains a set of other entries that share a common characteristic. 1020 Verify Message Integrity
Modes Of Introduction
Section HelpThe different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.
Phase Note
Architecture and Design OMISSION: This weakness is caused by missing a security tactic during the architecture and design phase.
Implementation
Applicable Platforms
Section HelpThis listing shows 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

Class: Not Language-Specific (Undetermined Prevalence)

Likelihood Of Exploit
Medium
Demonstrative Examples

Example 1


This example loads an external class from a local subdirectory.

(bad code)
Example Language: Java
URL[] classURLs= new URL[]{
new URL("file:subdir/")
};
URLClassLoader loader = new URLClassLoader(classURLs);
Class loadedClass = Class.forName("loadMe", true, loader);

This code does not ensure that the class loaded is the intended one, for example by verifying the class's checksum. An attacker may be able to modify the class file to execute malicious code.



Example 2


This code includes an external script to get database credentials, then authenticates a user against the database, allowing access to the application.

(bad code)
Example Language: PHP
//assume the password is already encrypted, avoiding CWE-312

function authenticate($username,$password){

include("http://external.example.com/dbInfo.php");

//dbInfo.php makes $dbhost, $dbuser, $dbpass, $dbname available
mysql_connect($dbhost, $dbuser, $dbpass) or die ('Error connecting to mysql');
mysql_select_db($dbname);
$query = 'Select * from users where username='.$username.' And password='.$password;
$result = mysql_query($query);

if(mysql_numrows($result) == 1){
mysql_close();
return true;
}
else{
mysql_close();
return false;
}

}

This code does not verify that the external domain accessed is the intended one. An attacker may somehow cause the external domain name to resolve to an attack server, which would provide the information for a false database. The attacker may then steal the usernames and encrypted passwords from real user login attempts, or simply allow themself to access the application without a real user account.

This example is also vulnerable to an Adversary-in-the-Middle AITM (CWE-300) attack.



Selected Observed Examples

Note: this is a curated list of examples for users to understand the variety of ways in which this weakness can be introduced. It is not a complete list of all CVEs that are related to this CWE entry.

Reference Description
Satellite phone does not validate its firmware image.
Chain: router's firmware update procedure uses curl with "-k" (insecure) option that disables certificate validation (CWE-295), allowing adversary-in-the-middle (AITM) compromise with a malicious firmware image (CWE-494).
OS does not verify authenticity of its own updates.
online poker client does not verify authenticity of its own updates.
anti-virus product does not verify automatic updates for itself.
VOIP phone downloads applications from web sites without verifying integrity.
Detection Methods
Method Details

Manual Analysis

This weakness can be detected using 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.

Specifically, manual static analysis is typically required to find the behavior that triggers the download of code, and to determine whether integrity-checking methods are in use.

Note:These may be more effective than strictly automated techniques. This is especially the case with weaknesses that are related to design and business rules.

Black Box

Use monitoring tools that examine the software's process as it interacts with the operating system and the network. This technique is useful in cases when source code is unavailable, if the software was not developed by you, or if you want to verify that the build phase did not introduce any new weaknesses. Examples include debuggers that directly attach to the running process; system-call tracing utilities such as truss (Solaris) and strace (Linux); system activity monitors such as FileMon, RegMon, Process Monitor, and other Sysinternals utilities (Windows); and sniffers and protocol analyzers that monitor network traffic.

Attach the monitor to the process and also sniff the network connection. Trigger features related to product updates or plugin installation, which is likely to force a code download. Monitor when files are downloaded and separately executed, or if they are otherwise read back into the process. Look for evidence of cryptographic library calls that use integrity checking.

Automated Static Analysis
Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

Effectiveness: High
Memberships
Section HelpThis 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.
Nature Type ID Name
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 752 2009 Top 25 - Risky Resource Management
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 802 2010 Top 25 - Risky Resource Management
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 859 The CERT Oracle Secure Coding Standard for Java (2011) Chapter 16 - Platform Security (SEC)
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 865 2011 Top 25 - Risky Resource Management
MemberOf ViewView - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries). 884 CWE Cross-section
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 991 SFP Secondary Cluster: Tainted Input to Environment
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1354 OWASP Top Ten 2021 Category A08:2021 - Software and Data Integrity Failures
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1364 ICS Communications: Zone Boundary Failures
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1411 Comprehensive Categorization: Insufficient Verification of Data Authenticity
Vulnerability Mapping Notes
Usage ALLOWED
(this CWE ID may be used to map to real-world vulnerabilities)
Reason Acceptable-Use

Rationale

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.

Comments

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.
Notes

Research Gap

This is critical for mobile code, but it is likely to become more and more common as developers continue to adopt automated, network-based product distributions and upgrades. Software-as-a-Service (SaaS) might introduce additional subtleties. Common exploitation scenarios may include ad server compromises and bad upgrades.
Taxonomy Mappings
Mapped Taxonomy Name Node ID Fit Mapped Node Name
CLASP Invoking untrusted mobile code
The CERT Oracle Secure Coding Standard for Java (2011) SEC06-J Do not rely on the default automatic signature verification provided by URLClassLoader and java.util.jar
Software Fault Patterns SFP27 Tainted input to environment
References
[REF-454] Microsoft. "Introduction to Code Signing".
<http://msdn.microsoft.com/en-us/library/ms537361(VS.85).aspx>.
[REF-455] Microsoft. "Authenticode".
<http://msdn.microsoft.com/en-us/library/ms537359(v=VS.85).aspx>.
[REF-456] Apple. "Code Signing Guide". Apple Developer Connection. 2008年11月19日.
<https://web.archive.org/web/20080724215143/http://developer.apple.com/documentation/Security/Conceptual/CodeSigningGuide/Introduction/chapter_1_section_1.html>. (URL validated: 2023年04月07日)
[REF-457] Anthony Bellissimo, John Burgess and Kevin Fu. "Secure Software Updates: Disappointments and New Challenges".
<https://www.usenix.org/legacy/events/hotsec06/tech/full_papers/bellissimo/bellissimo.pdf>. (URL validated: 2025年07月24日)
[REF-44] Michael Howard, David LeBlanc and John Viega. "24 Deadly Sins of Software Security". "Sin 18: The Sins of Mobile Code." Page 267. McGraw-Hill. 2010.
[REF-459] Johannes Ullrich. "Top 25 Series - Rank 20 - Download of Code Without Integrity Check". SANS Software Security Institute. 2010年04月05日.
<https://www.sans.org/blog/top-25-series-rank-20-download-of-code-without-integrity-check/>. (URL validated: 2023年04月07日)
[REF-76] Sean Barnum and Michael Gegick. "Least Privilege". 2005年09月14日.
<https://web.archive.org/web/20211209014121/https://www.cisa.gov/uscert/bsi/articles/knowledge/principles/least-privilege>. (URL validated: 2023年04月07日)
[REF-18] Secure Software, Inc.. "The CLASP Application Security Process". 2005.
<https://cwe.mitre.org/documents/sources/TheCLASPApplicationSecurityProcess.pdf>. (URL validated: 2024年11月17日)
[REF-1482] D3FEND. "D3FEND: D3-TL Trusted Library".
<https://d3fend.mitre.org/technique/d3f:TrustedLibrary/>. (URL validated: 2025年09月06日)
Content History
Submissions
Submission Date Submitter Organization
2006年07月19日
(CWE Draft 3, 2006年07月19日) 		CLASP
Modifications
Modification Date Modifier Organization
2025年09月09日
(CWE 4.18, 2025年09月09日) 		CWE Content Team MITRE
updated Potential_Mitigations, References
2024年02月29日
(CWE 4.14, 2024年02月29日) 		CWE Content Team MITRE
updated Demonstrative_Examples, Relationships
2023年06月29日 CWE Content Team MITRE
updated Mapping_Notes
2023年04月27日 CWE Content Team MITRE
updated Detection_Factors, References, Relationships
2023年01月31日 CWE Content Team MITRE
updated Related_Attack_Patterns
2022年10月13日 CWE Content Team MITRE
updated References, Related_Attack_Patterns
2021年10月28日 CWE Content Team MITRE
updated Observed_Examples, Relationships
2021年07月20日 CWE Content Team MITRE
updated Demonstrative_Examples
2021年03月15日 CWE Content Team MITRE
updated References, Related_Attack_Patterns
2020年12月10日 CWE Content Team MITRE
updated Demonstrative_Examples
2020年08月20日 CWE Content Team MITRE
updated Relationships
2020年02月24日 CWE Content Team MITRE
updated Demonstrative_Examples, Relationships
2019年06月20日 CWE Content Team MITRE
updated Related_Attack_Patterns, Relationships
2019年01月03日 CWE Content Team MITRE
updated Taxonomy_Mappings
2017年11月08日 CWE Content Team MITRE
updated Modes_of_Introduction, References, Relationships
2014年07月30日 CWE Content Team MITRE
updated Relationships, Taxonomy_Mappings
2012年10月30日 CWE Content Team MITRE
updated Potential_Mitigations
2012年05月11日 CWE Content Team MITRE
updated References, Relationships, Taxonomy_Mappings
2011年09月13日 CWE Content Team MITRE
updated Potential_Mitigations, References
2011年06月27日 CWE Content Team MITRE
updated Relationships
2011年06月01日 CWE Content Team MITRE
updated Common_Consequences, Relationships, Taxonomy_Mappings
2011年03月29日 CWE Content Team MITRE
updated Demonstrative_Examples
2010年12月13日 CWE Content Team MITRE
updated Potential_Mitigations
2010年09月27日 CWE Content Team MITRE
updated Potential_Mitigations, References
2010年06月21日 CWE Content Team MITRE
updated Common_Consequences, Detection_Factors, Potential_Mitigations, References
2010年04月05日 CWE Content Team MITRE
updated Applicable_Platforms
2010年02月16日 CWE Content Team MITRE
updated Detection_Factors, References, Relationships
2009年07月27日 CWE Content Team MITRE
updated Description, Observed_Examples, Related_Attack_Patterns
2009年03月10日 CWE Content Team MITRE
updated Potential_Mitigations
2009年01月12日 CWE Content Team MITRE
updated Applicable_Platforms, Common_Consequences, Description, Name, Other_Notes, Potential_Mitigations, References, Relationships, Research_Gaps, Type
2008年09月08日 CWE Content Team MITRE
updated Relationships, Other_Notes, Taxonomy_Mappings
2008年07月01日 Eric Dalci Cigital
updated Time_of_Introduction
Previous Entry Names
Change Date Previous Entry Name
2008年04月11日 Mobile Code: Invoking Untrusted Mobile Code
2009年01月12日 Download of Untrusted Mobile Code Without Integrity Check
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Page Last Updated: September 09, 2025

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