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 Class Draft
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.
Definition
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.
Auswirkungen in der Praxis
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.
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chain: Malformed input generates a regular expression error that leads to information exposure.
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Certain strings are later used in a regexp, leading to a resultant crash.
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MFV. Regular expression intended to protect against directory traversal reduces ".../...//" to "../".
-
Malformed regexp syntax leads to information exposure in error message.
Wie Angreifer es ausnutzen
Angreiferpfad Schritt für Schritt
- 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.
Verwundbares Codebeispiel
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!");
} Sicheres Codebeispiel
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.
Präventions-Checkliste
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.
Erkennungssignale
How to detect CWE-185
Plexicus erkennt CWE-185 automatisch und öffnet in unter 60 Sekunden einen Fix-PR.
Codex Remedium scannt jeden Commit, identifiziert genau diese Schwachstelle und liefert einen reviewer-ready Pull Request mit dem Patch. Keine Tickets. Keine Hand-offs.
Häufig gestellte Fragen Was ist CWE-185?
Wie gravierend ist CWE-185?
Welche Sprachen oder Plattformen sind von CWE-185 betroffen?
Wie kann ich CWE-185 verhindern?
Wie erkennt und behebt Plexicus CWE-185?
Wo erfahre ich mehr über CWE-185?
Frequently asked questions
Was ist 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.
Wie gravierend ist CWE-185?
MITRE hat für diese Schwachstelle keine Exploit-Wahrscheinlichkeit veröffentlicht. Behandle sie als mittlere Auswirkung, bis dein Threat Model anderes belegt.
Welche Sprachen oder Plattformen sind von CWE-185 betroffen?
MITRE hat für diese CWE keine betroffenen Plattformen spezifiziert — sie kann in den meisten Anwendungs-Stacks auftreten.
Wie kann ich CWE-185 verhindern?
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…
Wie erkennt und behebt Plexicus CWE-185?
Die SAST-Engine von Plexicus erkennt die Datenfluss-Signatur von CWE-185 bei jedem Commit. Bei einem Treffer öffnet unser Codex-Remedium-Agent einen Fix-PR mit korrigiertem Code, Tests und einer einzeiligen Zusammenfassung für den Reviewer.
Wo erfahre ich mehr über CWE-185?
MITRE veröffentlicht die kanonische Definition unter https://cwe.mitre.org/data/definitions/185.html. Für ergänzende Hinweise kannst du auch die OWASP- und NIST-Dokumentation heranziehen.
Verwandte Schwachstellen
Weaknesses related to CWE-185
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CWE-1025 Sibling
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CWE-1039 Sibling
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CWE-1077 Sibling
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CWE-1254 Sibling
Incorrect Comparison Logic Granularity
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CWE-183 Sibling
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CWE-581 Sibling
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