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How the mentioned CVE works (20 lines):
- Netty’s `HttpProxyHandler` constructs HTTP CONNECT requests for proxy tunneling.
- The `newInitialMessage()` method (line 176) creates headers using
DefaultHttpHeadersFactory.headersFactory().withValidation(false). - This explicitly disables CRLF validation, which was meant to be fixed by advisory GHSA-84h7-rjj3-6jx4.
- User-controlled `outboundHeaders` are passed via the `HttpProxyHandler` constructor.
- At lines 188‑190, `req.headers().add(outboundHeaders)` adds those headers without any sanitization.
- An attacker can inject CRLF sequences ( `\r\n` ) into header values.
- Because validation is off, the CRLF is not rejected or encoded.
- The injected CRLF terminates the current header and starts a new one.
- This allows arbitrary HTTP headers to be inserted into the CONNECT request.
- The proxy server receives the altered request, believing it to be legitimate.
- Example injection: `”1.2.3.4\r\nProxy-Authorization: Basic …”` adds a `Proxy-Authorization` header.
- This can bypass proxy authentication if the injected header overrides the original.
- Another attack: inject `Transfer-Encoding: chunked` and a smuggled request body.
- The proxy may then forward the smuggled request to an internal service.
- The root cause is an incomplete fix – GHSA-84h7-rjj3-6jx4 enabled validation globally, but `HttpProxyHandler` opted out.
- The `outboundHeaders` come directly from application code that might reflect user input.
- No CRLF checking occurs even for header values that contain newlines.
- The vulnerability affects all Netty versions prior to the patch (e.g., 4.2.12.Final and earlier).
- The attack requires that the application uses `HttpProxyHandler` with attacker‑influenced headers.
- Exploitation is remote, low complexity, and requires no privileges, leading to high integrity impact.
dailycve form:
Platform: Netty
Version: 4.2.12.Final
Vulnerability: HTTP Header Injection
Severity: High
date: 2026-05-07
Prediction: Patch expected 2026-06-15
What Undercode Say:
Check if your Netty version is vulnerable mvn dependency:tree | grep netty Extract HttpProxyHandler class jar xf netty-handler-4.2.12.Final.jar io/netty/handler/proxy/HttpProxyHandler.class javap -c io.netty.handler.proxy.HttpProxyHandler | grep -A5 "newInitialMessage" Test header validation status via reflection (simplified) echo "HttpHeadersFactory factory = DefaultHttpHeadersFactory.headersFactory(); boolean valid = factory.withValidation(false).isValidation(); echo $valid"
Exploit:
// Attacker-controlled user input
String malicious = "1.2.3.4\r\nX-Admin: true\r\nProxy-Authorization: Basic hacked";
HttpHeaders headers = new DefaultHttpHeaders(false);
headers.set("X-Forwarded-For", malicious);
new HttpProxyHandler(proxyAddr, headers);
// Resulting wire: CRLF injection creates extra headers.
Protection from this CVE:
- Upgrade to Netty version >= 4.2.13.Final (once patched).
- Remove `.withValidation(false)` in `HttpProxyHandler` (line 176) – use default factory.
- Validate all `outboundHeaders` manually with
HttpUtil.validateHeaderValue(). - Sanitize user input – reject or encode CRLF characters (
\r,\n). - Apply a WAF rule to block CRLF sequences in proxy requests.
Impact:
- Proxy Authentication Bypass – attacker injects `Proxy-Authorization` to gain unauthorized proxy access.
- Request Smuggling – injected `Transfer-Encoding` splits the request, leading to internal service compromise.
- Header Injection – arbitrary headers (e.g.,
X-Forwarded-For,Cookie) can be added, poisoning logs or altering backend behavior. - Integrity loss (High) – no confidentiality or availability impact, but data integrity is fully compromised.
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Sources:
Reported By: github.com
Extra Source Hub:
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