Overview
This report focuses on a critical vulnerability, CVE-2025-58056, found in certain versions of the Netty network application framework. This vulnerability is of significance due to Netty’s wide usage in the development of protocol servers and clients, and hence, it has the potential to affect a large number of network applications globally. The vulnerability allows attackers to conduct request smuggling attacks, which can lead to system compromise or data leakage.
Vulnerability Summary
CVE ID: CVE-2025-58056
Severity: High (7.5 CVSS Score)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: System compromise or data leakage
Affected Products
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Product | Affected Versions
Netty | 4.1.124.Final
Netty | 4.2.0.Alpha3 through 4.2.4.Final
How the Exploit Works
The exploit works by taking advantage of Netty’s incorrect handling of newline characters (LF) as a chunk-size line terminator. By crafting a request that reverse proxies parse as one request but Netty processes as two, attackers can perform request smuggling attacks. This discrepancy allows attackers to inject malicious content, which can lead to unauthorized system access or data exposure.
Conceptual Example Code
Here is a conceptual example of how an HTTP request smuggling attack might be crafted:
POST /vulnerable/endpoint HTTP/1.1
Host: target.example.com
Content-Length: 83
POST /internal/endpoint HTTP/1.1
Host: target.example.com
Content-Type: application/json
{ "malicious_payload": "..." }In this example, the attacker is sending what appears to be a single HTTP request to a vulnerable proxy server. However, due to the LF parsing error, Netty sees this as two separate requests. The second request, containing the malicious payload, is then processed by the target server.
Mitigation Guidance
To mitigate the vulnerability, users should update to versions 4.1.125.Final or 4.2.5.Final where the issue has been fixed. If patching is not immediately possible, deploying a Web Application Firewall (WAF) or an Intrusion Detection System (IDS) can serve as temporary mitigation.