The software receives data from an upstream component, but does not filter or incorrectly filters special elements before sending it to a downstream component.
Modes of Introduction:
– Implementation
Likelihood of Exploit:
Integrity: Unexpected State
The 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.
Modes of Introduction:
– Architecture and Design
Likelihood of Exploit: High
Access Control, Confidentiality: Bypass Protection Mechanism, Read Application Data
The most common attack performed with cross-site scripting involves the disclosure of information stored in user cookies. Typically, a malicious user will craft a client-side script, which — when parsed by a web browser — performs some activity (such as sending all site cookies to a given E-mail address). This script will be loaded and run by each user visiting the web site. Since the site requesting to run the script has access to the cookies in question, the malicious script does also.
Integrity, Confidentiality, Availability: Execute Unauthorized Code or Commands
In some circumstances it may be possible to run arbitrary code on a victim’s computer when cross-site scripting is combined with other flaws.
Confidentiality, Integrity, Availability, Access Control: Execute Unauthorized Code or Commands, Bypass Protection Mechanism, Read Application Data
The consequence of an XSS attack is the same regardless of whether it is stored or reflected. The difference is in how the payload arrives at the server. XSS can cause a variety of problems for the end user that range in severity from an annoyance to complete account compromise. Some cross-site scripting vulnerabilities can be exploited to manipulate or steal cookies, create requests that can be mistaken for those of a valid user, compromise confidential information, or execute malicious code on the end user systems for a variety of nefarious purposes. Other damaging attacks include the disclosure of end user files, installation of Trojan horse programs, redirecting the user to some other page or site, running “Active X” controls (under Microsoft Internet Explorer) from sites that a user perceives as trustworthy, and modifying presentation of content.
Phase: Architecture and Design
Effectiveness:
Description:
Phase: Implementation, Architecture and Design
Effectiveness:
Description:
Phase: Architecture and Design, Implementation
Effectiveness: Limited
Description:
Understand all the potential areas where untrusted inputs can enter your software: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide data to the application. Remember that such inputs may be obtained indirectly through API calls.
This technique has limited effectiveness, but can be helpful when it is possible to store client state and sensitive information on the server side instead of in cookies, headers, hidden form fields, etc.
Phase: Architecture and Design
Effectiveness:
Description:
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.
Phase: Architecture and Design
Effectiveness:
Description:
If available, use structured mechanisms that automatically enforce the separation between data and code. These mechanisms may be able to provide the relevant quoting, encoding, and validation automatically, instead of relying on the developer to provide this capability at every point where output is generated.
Phase: Implementation
Effectiveness:
Description:
Phase: Implementation
Effectiveness:
Description:
With Struts, write all data from form beans with the bean’s filter attribute set to true.
Phase: Implementation
Effectiveness: Defense in Depth
Description:
To help mitigate XSS attacks against the user’s session cookie, set the session cookie to be HttpOnly. In browsers that support the HttpOnly feature (such as more recent versions of Internet Explorer and Firefox), this attribute can prevent the user’s session cookie from being accessible to malicious client-side scripts that use document.cookie. This is not a complete solution, since HttpOnly is not supported by all browsers. More importantly, XMLHTTPRequest and other powerful browser technologies provide read access to HTTP headers, including the Set-Cookie header in which the HttpOnly flag is set.
Phase: Implementation
Effectiveness:
Description:
Phase: Architecture and Design
Effectiveness:
Description:
When the set of acceptable objects, such as filenames or URLs, is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames or URLs, and reject all other inputs.
Phase: Operation
Effectiveness: Moderate
Description:
Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth.
An application firewall might not cover all possible input vectors. In addition, attack techniques might be available to bypass the protection mechanism, such as using malformed inputs that can still be processed by the component that receives those inputs. Depending on functionality, an application firewall might inadvertently reject or modify legitimate requests. Finally, some manual effort may be required for customization.
Phase: Operation, Implementation
Effectiveness:
Description:
When using PHP, configure the application so that it does not use register_globals. During implementation, develop the 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.
The product allocates memory based on an untrusted, large size value, but it does not ensure that the size is within expected limits, allowing arbitrary amounts of memory to be allocated.
Modes of Introduction:
– Implementation
Likelihood of Exploit:
Availability: DoS: Resource Consumption (Memory)
Not controlling memory allocation can result in a request for too much system memory, possibly leading to a crash of the application due to out-of-memory conditions, or the consumption of a large amount of memory on the system.
Phase: Implementation, Architecture and Design
Effectiveness:
Description:
Perform adequate input validation against any value that influences the amount of memory that is allocated. Define an appropriate strategy for handling requests that exceed the limit, and consider supporting a configuration option so that the administrator can extend the amount of memory to be used if necessary.
Phase: Operation
Effectiveness:
Description:
Run your program using system-provided resource limits for memory. This might still cause the program to crash or exit, but the impact to the rest of the system will be minimized.
The software reads or writes to a buffer using an index or pointer that references a memory location after the end of the buffer.
This typically occurs when a pointer or its index is incremented to a position after the buffer; or when pointer arithmetic results in a position after the buffer.
Modes of Introduction:
Likelihood of Exploit:
Confidentiality: Read Memory
For an out-of-bounds read, the attacker may have access to sensitive information. If the sensitive information contains system details, such as the current buffers position in memory, this knowledge can be used to craft further attacks, possibly with more severe consequences.
Integrity, Availability: Modify Memory, DoS: Crash, Exit, or Restart
Out of bounds memory access will very likely result in the corruption of relevant memory, and perhaps instructions, possibly leading to a crash. Other attacks leading to lack of availability are possible, including putting the program into an infinite loop.
Integrity: Modify Memory, Execute Unauthorized Code or Commands
If the memory accessible by the attacker can be effectively controlled, it may be possible to execute arbitrary code, as with a standard buffer overflow. If the attacker can overwrite a pointer’s worth of memory (usually 32 or 64 bits), they can redirect a function pointer to their own malicious code. Even when the attacker can only modify a single byte arbitrary code execution can be possible. Sometimes this is because the same problem can be exploited repeatedly to the same effect. Other times it is because the attacker can overwrite security-critical application-specific data — such as a flag indicating whether the user is an administrator.
The software writes data past the end, or before the beginning, of the intended buffer.
Typically, this 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.
Modes of Introduction:
– Implementation
Likelihood of Exploit: High
CWE-119
CWE-119
CWE-119
CWE-119
Integrity, Availability: Modify Memory, DoS: Crash, Exit, or Restart, Execute Unauthorized Code or Commands
Phase: Requirements
Effectiveness:
Description:
Phase: Architecture and Design
Effectiveness:
Description:
This is not a complete solution, since many buffer overflows are not related to strings.
Phase: Build and Compilation
Effectiveness: Defense in Depth
Description:
This is not necessarily a complete solution, since these mechanisms can only detect certain types of overflows. In addition, an attack could still cause a denial of service, since the typical response is to exit the application.
Phase: Implementation
Effectiveness:
Description:
Phase: Operation
Effectiveness: Defense in Depth
Description:
This is not a complete solution. However, it forces the attacker to guess an unknown value that changes every program execution. In addition, an attack could still cause a denial of service, since the typical response is to exit the application.
Phase: Operation
Effectiveness: Defense in Depth
Description:
Use a CPU and operating system that offers Data Execution Protection (NX) or its equivalent [REF-60] [REF-61].
This is not a complete solution, since buffer overflows could be used to overwrite nearby variables to modify the software’s state in dangerous ways. In addition, it cannot be used in cases in which self-modifying code is required. Finally, an attack could still cause a denial of service, since the typical response is to exit the application.
Phase: Implementation
Effectiveness: Moderate
Description:
Replace unbounded copy functions with analogous functions that support length arguments, such as strcpy with strncpy. Create these if they are not available.
This approach is still susceptible to calculation errors, including issues such as off-by-one errors (CWE-193) and incorrectly calculating buffer lengths (CWE-131).
The software reads or writes to a buffer using an index or pointer that references a memory location prior to the beginning of the buffer.
This typically occurs when a pointer or its index is decremented to a position before the buffer, when pointer arithmetic results in a position before the beginning of the valid memory location, or when a negative index is used.
Modes of Introduction:
Likelihood of Exploit:
Confidentiality: Read Memory
For an out-of-bounds read, the attacker may have access to sensitive information. If the sensitive information contains system details, such as the current buffers position in memory, this knowledge can be used to craft further attacks, possibly with more severe consequences.
Integrity, Availability: Modify Memory, DoS: Crash, Exit, or Restart
Out of bounds memory access will very likely result in the corruption of relevant memory, and perhaps instructions, possibly leading to a crash.
Integrity: Modify Memory, Execute Unauthorized Code or Commands
If the corrupted memory can be effectively controlled, it may be possible to execute arbitrary code. If the corrupted memory is data rather than instructions, the system will continue to function with improper changes, possibly in violation of an implicit or explicit policy.
The software invokes a function for normalizing paths or file names, but it provides an output buffer that is smaller than the maximum possible size, such as PATH_MAX.
Passing an inadequately-sized output buffer to a path manipulation function can result in a buffer overflow. Such functions include realpath(), readlink(), PathAppend(), and others.
Windows provides a large number of utility functions that manipulate buffers containing filenames. In most cases, the result is returned in a buffer that is passed in as input. (Usually the filename is modified in place.) Most functions require the buffer to be at least MAX_PATH bytes in length, but you should check the documentation for each function individually. If the buffer is not large enough to store the result of the manipulation, a buffer overflow can occur.
Modes of Introduction:
– Implementation
Likelihood of Exploit:
Integrity, Confidentiality, Availability: Modify Memory, Execute Unauthorized Code or Commands, DoS: Crash, Exit, or Restart
Phase: Implementation
Effectiveness:
Description:
Always specify output buffers large enough to handle the maximum-size possible result from path manipulation functions.
The application uses a protection mechanism that relies on the existence or values of a cookie, but it does not properly ensure that the cookie is valid for the associated user.
Attackers can easily modify cookies, within the browser or by implementing the client-side code outside of the browser. Attackers can bypass protection mechanisms such as authorization and authentication by modifying the cookie to contain an expected value.
Modes of Introduction:
– Architecture and Design
Likelihood of Exploit: High
Access Control: Bypass Protection Mechanism, Gain Privileges or Assume Identity
It is dangerous to use cookies to set a user’s privileges. The cookie can be manipulated to claim a high level of authorization, or to claim that successful authentication has occurred.
Phase: Architecture and Design
Effectiveness:
Description:
Avoid using cookie data for a security-related decision.
Phase: Implementation
Effectiveness:
Description:
Perform thorough input validation (i.e.: server side validation) on the cookie data if you’re going to use it for a security related decision.
Phase: Architecture and Design
Effectiveness:
Description:
Add integrity checks to detect tampering.
Phase: Architecture and Design
Effectiveness:
Description:
Protect critical cookies from replay attacks, since cross-site scripting or other attacks may allow attackers to steal a strongly-encrypted cookie that also passes integrity checks. This mitigation applies to cookies that should only be valid during a single transaction or session. By enforcing timeouts, you may limit the scope of an attack. As part of your integrity check, use an unpredictable, server-side value that is not exposed to the client.
The program uses an expression in which operator precedence causes incorrect logic to be used.
While often just a bug, operator precedence logic errors can have serious consequences if they are used in security-critical code, such as making an authentication decision.
Modes of Introduction:
– Implementation
Likelihood of Exploit: Low
Confidentiality, Integrity, Availability: Varies by Context, Unexpected State
The consequences will vary based on the context surrounding the incorrect precedence. In a security decision, integrity or confidentiality are the most likely results. Otherwise, a crash may occur due to the software reaching an unexpected state.
Phase: Implementation
Effectiveness:
Description:
Regularly wrap sub-expressions in parentheses, especially in security-critical code.
The software implements an IOCTL with functionality that should be restricted, but it does not properly enforce access control for the IOCTL.
Modes of Introduction:
– Architecture and Design
Likelihood of Exploit:
Integrity, Availability, Confidentiality:
Attackers can invoke any functionality that the IOCTL offers. Depending on the functionality, the consequences may include code execution, denial-of-service, and theft of data.
Phase: Architecture and Design
Effectiveness:
Description:
In Windows environments, use proper access control for the associated device or device namespace. See References.