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How the Mentioned CVE Works:
The vulnerability in the `golang.org/x/net` library arises due to improper handling of IPv6 Zone IDs when matching hosts against proxy patterns. Specifically, when the `NO_PROXY` environment variable is configured to exclude certain domains (e.g., .example.com), the library incorrectly interprets an IPv6 address with a Zone ID as a hostname component. For instance, a request to `
:80` is mistakenly matched against the `NO_PROXY` pattern, causing the request to bypass the proxy. This flaw allows an attacker to manipulate requests to unintended destinations, potentially leading to unauthorized access or data leakage.
<h2 style="color: blue;">DailyCVE Form:</h2>
Platform: Golang (golang.org/x/net)
Version: Pre-2025 patches
Vulnerability: Proxy Bypass via IPv6 Zone IDs
Severity: Moderate
Date: Mar 12, 2025
<h2 style="color: blue;">What Undercode Say:</h2>
<h2 style="color: blue;">Exploitation:</h2>
<ol>
<li>Crafting Malicious Requests: Attackers can craft HTTP requests with IPv6 addresses containing Zone IDs to bypass proxy restrictions.
Example: `http://[bash]:80`</li>
<li>Environment Manipulation: Exploit the `NO_PROXY` environment variable to force requests to unintended destinations.</li>
<li>Network Interception: Use this flaw to redirect traffic to malicious servers, enabling man-in-the-middle attacks.
<h2 style="color: blue;">Protection:</h2></li>
<li>Update Libraries: Ensure `golang.org/x/net` is updated to the latest patched version.
<h2 style="color: blue;">Command: <code>go get -u golang.org/x/net</code></h2></li>
<li>Input Validation: Sanitize and validate IPv6 addresses to prevent misuse of Zone IDs.</li>
<li>Proxy Configuration: Review and tighten `NO_PROXY` settings to avoid ambiguous patterns.</li>
</ol>
<h2 style="color: blue;">Code Snippets:</h2>
<h2 style="color: blue;">1. Patch Implementation:</h2>
[bash]
// Updated host matching logic
if strings.Contains(host, "%25") {
return false // Reject IPv6 Zone IDs in hostnames
}
2. Exploit Simulation:
curl -x http://proxy.example.com http://[bash]:80
3. Environment Hardening:
export NO_PROXY=".example.com,localhost"
Analytics:
- Impact: Moderate risk of proxy bypass leading to unauthorized access.
- Affected Systems: Applications using `golang.org/x/net` for HTTP proxy handling.
- Mitigation Difficulty: Low; requires library updates and configuration reviews.
Commands:
1. Check Installed Version:
go list -m golang.org/x/net
2. Force Update:
go get golang.org/x/net@latest
3. Test Proxy Bypass:
curl -v -x http://proxy.example.com http://[bash]:80
By following these steps, developers can mitigate the risk of proxy bypass vulnerabilities in their Go applications.
References:
Reported By: https://github.com/advisories/GHSA-qxp5-gwg8-xv66
Extra Source Hub:
Undercode
