The Homeland Security Systems Engineering and Development Institute (HSSEDI), has released the 2020 Common Weakness Enumeration (CWE) Top 25 Most Dangerous Software Weaknesses list.
HSSEDI, sponsored by the Department of Homeland Security and operated by MITRE, released the 2020 CWE Top 25 list as of “the most common and impactful issues experienced over the previous two calendar years.”
“These weaknesses are dangerous because they are often easy to find, exploit, and can allow adversaries to completely take over a system, steal data, or prevent an application from working,” the experts explained in the CWE online post.
The CWE Top 25 can assist developers, security researchers, educators and other professionals with valuable insight into the most critical security weaknesses.
2020 CWE Top 25 list
The CWE Top 25 list outlines those top critical weaknesses based on common Vulnerabilities and Exposures (CVE) data discovered in the National Institute of Standards and Technology (NIST) National Vulnerability Database (NVD). In addition, the list leverages the Common Vulnerability Scoring System (CVSS) scores associated with each vulnerability.
The Top 25 weaknesses are listed below in order of highest “weakness score,” based on prevalence and severity.
- CWE-79: Improper Neutralization of Input During Web Page Generation (‘Cross-site Scripting’) – 46.82
- CWE-787: Out-of-bounds Write – 46.17
- CWE-20: Improper Input Validation – 33.47
- CWE-125: Out-of-bounds Read – 26.5
- CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer – 23.73
- CWE-89: Improper Neutralization of Special Elements used in an SQL Command (‘SQL Injection’) – 20.69
- CWE-200: Exposure of Sensitive Information to an Unauthorized Actor – 19.16
- CWE-416: Use After Free – 18.87
- CWE-352: Cross-Site Request Forgery (CSRF) – 17.29
- CWE-78: Improper Neutralization of Special Elements used in an OS Command (‘OS Command Injection’) – 16.44
- CWE-190: Integer Overflow or Wraparound – 15.81
- CWE-22: Improper Limitation of a Pathname to a Restricted Directory (‘Path Traversal’) – 13.67
- CWE-476: NULL Pointer Dereference – 8.35
- CWE-287: Improper Authentication – 8.17
- CWE-434: Unrestricted Upload of File with Dangerous Type – 7.38
- CWE-732: Incorrect Permission Assignment for Critical Resource – 6.95
- CWE-94: Improper Control of Generation of Code (‘Code Injection’) – 6.53
- CWE-522: Insufficiently Protected Credentials – 5.49
- CWE-611: Improper Restriction of XML External Entity Reference – 5.33
- CWE-798: Use of Hard-coded Credentials – 5.19
- CWE-502: Deserialization of Untrusted Data – 4.93
- CWE-269: Improper Privilege Management – 4.87
- CWE-400: Uncontrolled Resource Consumption – 4.14
- CWE-306: Missing Authentication for Critical Function – 3.85
- CWE-862: Missing Authorization – 3.77
In this article, we have summarized the CWE software weaknesses below, along with a brief synopsis of each.
1) CWE-79 Improper Neutralization of Input During Web Page Generation (‘Cross-site Scripting’)
Improper Neutralization of Input During Web Page Generation (‘Cross-site Scripting’) occurs when “software does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.”
According to CWE-79, Cross-site scripting (also known as “XSS”) consists of three main types:
- Type 1:Reflected XSS (or Non-Persistent)
- Type 2: Stored XSS (or Persistent) also known as “HTML injection”
- Type 0: DOM-Based XSS.
An attacker could inject a malicious script (into as web app for example) and then perform variety of malicious activities such as
Once the malicious script is injected, the attacker can perform a variety of malicious activities, such as stealing private information, launch phishing attacks or exploit vulnerabilities in victim’s web browser.
2) CWE-787 Out-of-bounds Write
The Out-of-bounds Write occurs when software writes data past the end, or before the beginning, of the intended buffer, according to CVE.
As explained in more detail in CWE-787, this software weakness “can result in corruption of data, a crash, or code execution. The software may modify an index or perform pointer arithmetic that references a memory location that is outside of the boundaries of the buffer. A subsequent write operation then produces undefined or unexpected results.”
3) CWE-20 Improper Input Validation
Improper Input Validation occurs when the “product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.”
According to CWE-20, Improper input validation may result in altered control flow, arbitrary control of a resource, or arbitrary code execution.
4) CWE-125 Out-of-bounds Read
An Out-of-bounds Read vulnerability occurs when software reads data past the end, or before the beginning, of the intended buffer.
According to CWE-125, this software flaw “can allow attackers to read sensitive information from other memory locations or cause a crash. A crash can occur when the code reads a variable amount of data and assumes that a sentinel exists to stop the read operation, such as a NUL in a string.”
5) CWE-119 Improper Restriction of Operations within the Bounds of a Memory Buffer
According to CWE-119, an Improper Restriction of Operations within the Bounds of a Memory Buffer weakness occurs when the software “performs operations on a memory buffer, but it can read from or write to a memory location that is outside of the intended boundary of the buffer.”
As a consequence, an attacker could then exploit to execute arbitrary code, alter the intended control flow, read sensitive information, or cause the system to crash.
6) CWE-89 Improper Neutralization of Special Elements used in an SQL Command (‘SQL Injection’)
According to CWE-89, a SQL Injection weakness exists when the “software constructs all or part of an SQL command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended SQL command when it is sent to a downstream component.”
As a consequence, an attacker could then alter query logic to bypass security checks or even insert additional statements that modify the back-end database and execute system commands.
This issue is also most common in database-driven websites.
7) CWE-200 Exposure of Sensitive Information to an Unauthorized Actor
According to CWE-200, exposure of sensitive information exists when software “exposes sensitive information to an actor that is not explicitly authorized to have access to that information.”
Often times, this weakness can be caused by coding mistakes such as:
- Lack of scrubbing or sanitizing data (explicitly inserts)
- Web script errors that reveal the full system path of the program (indirectly inserts).
- Unintentionally made accessible to unauthorized actors (such as web resources open to public internet).
To add, “information disclosure” is also sometimes used as an an alternate term for this flaw or related vulnerabilities.
8) CWE-416 Use After Free
According to CWE-416, Use After Free weakness occurs when software “references memory after it has been freed can cause a program to crash, use unexpected values, or execute code.”
Also known as “dangling pointer,” use after free errors can occur when:
- Error conditions and other exceptional circumstances.
- Confusion over which part of the program is responsible for freeing the memory.
9) CWE-352 Cross-Site Request Forgery (CSRF)
According to CWE-352, Cross-Site Request Forgery (CSRF) happens when a “web application does not, or can not, sufficiently verify whether a well-formed, valid, consistent request was intentionally provided by the user who submitted the request.”
CSRF is also known by terms XSRF, Cross Site Reference Forgery and Session Riding.
10) CWE-78: Improper Neutralization of Special Elements used in an OS Command (‘OS Command Injection’)
According to CWE-78, ‘OS Command Injection’ occurs when the software “constructs all or part of an OS command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended OS command when it is sent to a downstream component.”
OS Command Injection has also gone by the terms Shell injection and Shell metacharacters.
11) CWE-190: Integer Overflow or Wraparound
According to CWE-190, Integer Overflow or Wraparound exists when “software performs a calculation that can produce an integer overflow or wraparound, when the logic assumes that the resulting value will always be larger than the original value. This can introduce other weaknesses when the calculation is used for resource management or execution control.”
12) CWE-22: Improper Limitation of a Pathname to a Restricted Directory (‘Path Traversal’)
According to CWE-22, ‘Path Traversal’ occurs when “software uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the software does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.”
Attackers can use use special elements such as “..” and “/” separators to escape outside of the restricted location and gain access to sensitive files or directories hosted on the system.
Alternate terms include Directory traversal and Path traversal.
13) CWE-476: NULL Pointer Dereference
According to CWE-476, NULL Pointer Dereference exists when the “application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.”
Furthermore, this software weakness can be caused by race conditions and simple programming omission flaws.
14) CWE-287: Improper Authentication
According to CWE-287, Improper Authentication occurs when a bad actor “claims to have a given identity, the software does not prove or insufficiently proves that the claim is correct.”
Alternative terms include “authentification” (often used in non-English speaking countries) and AuthC.
15) CWE-434: Unrestricted Upload of File with Dangerous Type
According to CWE-434, Unrestricted Upload of File with Dangerous Type happens when software “allows the attacker to upload or transfer files of dangerous types that can be automatically processed within the product’s environment.”
“Unrestricted file upload” is also used as an alternate term, but can be confused with related but different resource consumption vulnerabilities that are caused by lack of restrictions on the size or number of uploaded files.
16) CWE-732: Incorrect Permission Assignment for Critical Resource
According to CWE-732, Incorrect Permission Assignment for Critical Resource exists when software “specifies permissions for a security-critical resource in a way that allows that resource to be read or modified by unintended actors.”
To add, CWE warns this flaw is especially dangerous when the resource is related to program configuration, execution or sensitive user data.
17) CWE-94: Improper Control of Generation of Code (‘Code Injection’)
According to CWE-94, ‘Code Injection’ weakness occurs when the software “constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment.”
To add, an attacker could craft code to alter the intended control flow of the software and also lead to arbitrary code execution.
18) CWE-522: Insufficiently Protected Credentials
According to CWE-522, Insufficiently Protected Credentials exists when the product “transmits or stores authentication credentials, but it uses an insecure method that is susceptible to unauthorized interception and/or retrieval.”
19) CWE-611: Improper Restriction of XML External Entity Reference
According to CWE-611, Improper Restriction of XML External Entity Reference happens when software “processes an XML document that can contain XML entities with URIs that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output.”
As a result, an attacker can submit an XML file that defines an external entity with a file:// URI, thus cause the processing application to read the contents of a local file.
20) CWE-798: Use of Hard-coded Credentials
According to CWE-798, Use of Hard-coded Credentials occurs when the software “contains hard-coded credentials, such as a password or cryptographic key, which it uses for its own inbound authentication, outbound communication to external components, or encryption of internal data.”
Attackers can exploit hard-coded credentials, a significant hole, to bypass authentication configured by software administrators.
21) CWE-502: Deserialization of Untrusted Data
According to CWE-502, this software flaw exists when an application “deserializes untrusted data without sufficiently verifying that the resulting data will be valid.”
Alternate terms include Unmarshaling, Unpickling (Python functionality) and PHP Object Injection (PHP apps).
22) CWE-269: Improper Privilege Management
According to CWE-269, Improper Privilege Management occurs when software “does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor.”
23) CWE-400: Uncontrolled Resource Consumption
According to CWE-400, Uncontrolled Resource Consumption exists when software “does not properly control the allocation and maintenance of a limited resource, thereby enabling an actor to influence the amount of resources consumed, eventually leading to the exhaustion of available resources.”
Bad actors could take advantage of limited resources, such as memory, file storage and CPU, if software does not control or limit the number or size of the resources. As a result, actors could cause a denial of service (DoS) that consumes all available resources and cause a system crash.
24) CWE-306: Missing Authentication for Critical Function
According to CWE-306, Missing Authentication for Critical Function happens when the software “does not perform any authentication for functionality that requires a provable user identity or consumes a significant amount of resources.”
For example, attackers could exploit exposed critical functionality to gain the same privileged level of the functionality. As a consequence, they could read/modify sensitive data, access administrative functionality or even execute arbitrary code.
25) CWE-862: Missing Authorization
According to CWE-862, Missing Authorization occurs when the software “does not perform an authorization check when an actor attempts to access a resource or perform an action.”
Also known as “AuthZ”, Authorization is the process of determining whether that user can access a given resource, based on the user’s privileges and access control permissions applicable to the resource.
As a consequence, AuthZ flaws can lead to information exposure, denial of service and arbitrary code execution.
Finally, readers can check out related OWASP Top 10 web application security risks, as well as OWASP API Security Top 10 2019.