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.)
CWE-185 Clase Borrador
Incorrect Regular Expression
This vulnerability occurs when a regular expression is written incorrectly, causing it to match or validate data in unintended and potentially dangerous ways.
Definición
What is CWE-185?
This vulnerability occurs when a regular expression is written incorrectly, causing it to match or validate data in unintended and potentially dangerous ways.
Incorrect regular expressions are a common source of security flaws because they often fail to properly filter or validate user input. When used in security controls—like input sanitization, access rules, or data validation—a flawed regex pattern can allow malicious data to slip through, bypassing critical protections. This can lead directly to injection attacks, authorization bypasses, or data corruption.
Finding and fixing these subtle regex errors manually is time-consuming, especially in large codebases. While SAST tools can flag the problematic pattern, an ASPM platform like Plexicus uses AI to analyze the context and provide specific, automated remediation advice, helping developers apply the correct fix quickly and consistently across the entire application portfolio.
Impacto en el mundo real
Real-world CVEs caused by CWE-185
-
Regexp isn't "anchored" to the beginning or end, which allows spoofed values that have trusted values as substrings.
-
Regexp for IP address isn't anchored at the end, allowing appending of shell metacharacters.
-
Bypass access restrictions via multiple leading slash, which causes a regular expression to fail.
-
Local user DoS via invalid regular expressions.
-
chain: Malformed input generates a regular expression error that leads to information exposure.
-
Certain strings are later used in a regexp, leading to a resultant crash.
-
MFV. Regular expression intended to protect against directory traversal reduces ".../...//" to "../".
-
Malformed regexp syntax leads to information exposure in error message.
Cómo lo explotan los atacantes
Ruta del atacante paso a paso
- 1
The following code takes phone numbers as input, and uses a regular expression to reject invalid phone numbers.
- 2
An attacker could provide an argument such as: "; ls -l ; echo 123-456" This would pass the check, since "123-456" is sufficient to match the "\d+-\d+" portion of the regular expression.
- 3
This code uses a regular expression to validate an IP string prior to using it in a call to the "ping" command.
- 4
Since the regular expression does not have anchors (CWE-777), i.e. is unbounded without ^ or $ characters, then prepending a 0 or 0x to the beginning of the IP address will still result in a matched regex pattern. Since the ping command supports octal and hex prepended IP addresses, it will use the unexpectedly valid IP address (CWE-1389). For example, "0x63.63.63.63" would be considered equivalent to "99.63.63.63". As a result, the attacker could potentially ping systems that the attacker cannot reach directly.
Ejemplo de código vulnerable
Vulnerable Perl
The following code takes phone numbers as input, and uses a regular expression to reject invalid phone numbers.
$phone = GetPhoneNumber();
if ($phone =~ /\d+-\d+/) {
```
# looks like it only has hyphens and digits*
system("lookup-phone $phone");}
else {
```
error("malformed number!");
} Ejemplo de código seguro
Secure pseudo
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
const safe = validateAndEscape(input);
return executeWithGuards(safe);
} What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Lista de prevención
How to prevent CWE-185
- Architecture and Design Regular expressions can become error prone when defining a complex language even for those experienced in writing grammars. Determine if several smaller regular expressions simplify one large regular expression. Also, subject the regular expression to thorough testing techniques such as equivalence partitioning, boundary value analysis, and robustness. After testing and a reasonable confidence level is achieved, a regular expression may not be foolproof. If an exploit is allowed to slip through, then record the exploit and refactor the regular expression.
Señales de detección
How to detect CWE-185
Plexicus detecta automáticamente CWE-185 y abre un PR de corrección en menos de 60 segundos.
Codex Remedium escanea cada commit, identifica esta debilidad concreta y entrega un pull request listo para revisión con el parche. Sin tickets. Sin traspasos.
Preguntas frecuentes ¿Qué es CWE-185?
¿Qué gravedad tiene CWE-185?
¿Qué lenguajes o plataformas se ven afectados por CWE-185?
¿Cómo puedo prevenir CWE-185?
¿Cómo detecta y corrige Plexicus CWE-185?
¿Dónde puedo aprender más sobre CWE-185?
Frequently asked questions
¿Qué es CWE-185?
This vulnerability occurs when a regular expression is written incorrectly, causing it to match or validate data in unintended and potentially dangerous ways.
¿Qué gravedad tiene CWE-185?
MITRE no ha publicado una calificación de probabilidad de explotación para esta debilidad. Trátala como de impacto medio hasta que tu modelo de amenazas demuestre lo contrario.
¿Qué lenguajes o plataformas se ven afectados por CWE-185?
MITRE no ha especificado plataformas afectadas para esta CWE — puede aplicar a la mayoría de los stacks de aplicaciones.
¿Cómo puedo prevenir CWE-185?
Regular expressions can become error prone when defining a complex language even for those experienced in writing grammars. Determine if several smaller regular expressions simplify one large regular expression. Also, subject the regular expression to thorough testing techniques such as equivalence partitioning, boundary value analysis, and robustness. After testing and a reasonable confidence level is achieved, a regular expression may not be foolproof. If an exploit is allowed to slip…
¿Cómo detecta y corrige Plexicus CWE-185?
El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-185 en cada commit. Cuando hay coincidencia, nuestro agente Codex Remedium abre un PR de corrección con el código corregido, las pruebas y un resumen de una línea para el revisor.
¿Dónde puedo aprender más sobre CWE-185?
MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/185.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.
Debilidades relacionadas
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