# Cwe 93 Crlf Injection

> Use this skill when you need to remediate CWE-93 (CRLF Injection) vulnerabilities in Java code. Triggers on SAST findings, security reviews, or when fixing crlf injection issues.

- Skill: `developerscoffee/cwe-93-crlf-injection` (Agent Skill)
- Install (CLI): `npx skillmds@latest add developerscoffee/cwe-93-crlf-injection`
- Raw SKILL.md: https://api.skillmd.com/api/skills/developerscoffee/cwe-93-crlf-injection/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Security
- License: MIT
- Author: DevelopersCoffee (https://skillmd.com/u/developerscoffee)
- Updated: 2026-09-10
- Page: https://skillmd.com/skills/developerscoffee/cwe-93-crlf-injection

---


# CWE-93 CRLF Injection

## Description

CRLF Injection

Reference:
https://cwe.mitre.org/data/definitions/93.html


**OWASP Category**: A03:2021 – Injection


---

## Vulnerable Pattern


### ❌ Example 1: Vulnerable Pattern

```java
// VULNERABLE: User input directly in header
response.setHeader("X-Custom", userInput);
// VULNERABLE: CRLF in redirect
response.sendRedirect(userUrl);
```


**Why it's vulnerable:** This pattern is vulnerable to CRLF Injection




---

## Deterministic Fix


### ✅ Secure Implementation: Secure Implementation

```java
// SECURE: Remove CR/LF characters
String safeValue = userInput.replaceAll("[\\r\\n]", "");
response.setHeader("X-Custom", safeValue);

// For URLs, use URL encoding
String safeUrl = URLEncoder.encode(userUrl, StandardCharsets.UTF_8);
```


**Why it's secure:** Implements proper protection against CRLF Injection




---

## Detection Pattern

Look for these patterns in your codebase:


```bash
# Find setHeader with user input
grep -rn "setHeader.*getParameter\\|addHeader.*request" --include="*.java"
```



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## Remediation Steps


1. Strip CR (\r) and LF (\n) from all header values

2. URL-encode user input used in redirects

3. Use framework-provided methods that auto-sanitize


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## Key Imports

```java

import java.net.URLEncoder;

import java.nio.charset.StandardCharsets;

```

---

## Verification

After remediation:


- Run SAST scanner to confirm vulnerability is resolved

- Review all instances of the vulnerable pattern

- Add unit tests that verify the secure implementation

- Check for similar patterns in related code


---

## Trigger Examples

```
Fix CWE-93 vulnerability
Resolve CRLF Injection issue
Secure this Java code against crlf injection
SAST reports CWE-93
```

---

## Common Vulnerable Locations

| Layer | Files | Patterns |
|-------|-------|----------|

| Controller | `*Controller.java` | User input handling |

| Service | `*Service.java` | Business logic |

| Repository | `*Repository.java` | Data access |


---

## References


- [CWE-93: CRLF Injection](https://cwe.mitre.org/data/definitions/93.html)


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**Source**: Generated by [Java CWE Security Skills Generator](https://github.com/DevelopersCoffee/java-cwe-security-skills)
**Last Updated**: 2026-03-07