Weakness (CWE)
CWE-138: Improper Neutralization of Special Elements
The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could be interpreted as control elements or syntactic markers when they are sent to a downstream component.
More detail
Most languages and protocols have their own special elements such as characters and reserved words. These special elements can carry control implications. If product does not prevent external control or influence over the inclusion of such special elements, the control flow of the program may be altered from what was intended. For example, both Unix and Windows interpret the symbol < ("less than") as meaning "read input from a file".
How to prevent it (5 mitigations)
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Implementation
Developers should anticipate that special elements (e.g. delimiters, symbols) will be injected into input vectors of their product. One defense is to create an allowlist (e.g. a regular expression) that defines valid input according to the requirements specifications. Strictly filter any input that does not match against the allowlist. Properly encode your output, and quote any elements that have special meaning to the component with which you are communicating.
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Implementation
Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list 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. This 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, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
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Implementation
Use and specify an appropriate output encoding to ensure that the special elements are well-defined. A normal byte sequence in one encoding could be a special element in another.
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Implementation
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 allowlist validation schemes by introducing dangerous inputs after they have been checked.
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Implementation
While it is risky to use dynamically-generated query strings, code, or commands that mix control and data together, sometimes it may be unavoidable. Properly quote arguments and escape any special characters within those arguments. The most conservative approach is to escape or filter all characters that do not pass an extremely strict allowlist (such as everything that is not alphanumeric or white space). If some special characters are still needed, such as white space, wrap each argument in quotes after the escaping/filtering step. Be careful of argument injection (CWE-88).
Source: MITRE CWE-138
14 results · Feed
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High 7.5
Graylog: Fortigate syslog message parser can be exploited to modify or delete fields from the original message
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High 7.5
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High 7.5
.NET Spoofing Vulnerability
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Medium 5.3
Cisco Secure Firewall Adaptive Security Appliance SSH Partial Private Key Authentication Bypass Vulnerability
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Medium 4.2
tarteaucitron.js vulnerable to DOM Clobbering via document.currentScript
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High 7.3CVE-2025-5878 Public exploit
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A vulnerability was found in ESAPI esapi-java-legacy and classified as problematic. This issue affects the interface Encoder.encodeForSQL of the SQL Injection Defense. An attack leads to an improper neutralization of special elements. The attack may be initia…
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Medium 5.3
Failure to check for packets from the broadcast address allows potential DDoS amplification attack in Meshtastic firmware
Meshtastic firmware is a device firmware for the Meshtastic project. The Meshtastic firmware does not check for packets claiming to be from the special broadcast address (0xFFFFFFFF) which could result in unexpected behavior and potential for DDoS attacks on …
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High 7.8
Windows Kernel Elevation of Privilege Vulnerability
Windows Kernel Elevation of Privilege Vulnerability
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High 7.5
Insufficient data validation in Permission Prompts in Google Chrome prior to 117.0.5938.62 allowed an attacker who conv…
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High 8.1
Exim Improper Neutralization of Special Elements Remote Code Execution Vulnerability
Exim Improper Neutralization of Special Elements Remote Code Execution Vulnerability. This vulnerability allows remote attackers to execute arbitrary code on affected installations of Exim. Authentication is not required to exploit this vulnerability. The spe…
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Medium 6.8
Email HTML Injection
HTML Email Injection in Tribe29 Checkmk <=2.1.0p23; <=2.0.0p34, and all versions of Checkmk 1.6.0 allows an authenticated attacker to inject malicious HTML into Emails
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Medium 6.5
Ultimate SMS Notifications for WooCommerce <= 1.4.1 - CSV Injection
The Ultimate SMS Notifications for WooCommerce plugin for WordPress is vulnerable to CSV Injection in versions up to, and including, 1.4.1 via the 'Export Utility' functionality. This makes it possible for authenticated attackers, such as a subscriber, to add…
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High 7.2
PAN-OS: Improper Neutralization Vulnerability Leads to Unintended Program Execution During Configuration Commit
A vulnerability exists in Palo Alto Networks PAN-OS software that enables an authenticated network-based PAN-OS administrator to upload a specifically created configuration that disrupts system processes and potentially execute arbitrary code with root privil…
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Medium 4.2
Infinispan: Deserialization of untrusted data in the Hot Rod Java client via automatic byte-array deserialization
The hotrod java client in infinispan before 9.1.0.Final automatically deserializes bytearray message contents in certain events. A malicious user could exploit this flaw by injecting a specially-crafted serialized object to attain remote code execution or con…