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CVE-2021-21295— Possible request smuggling in HTTP/2 due missing validation

Quick assessment

Affected
netty io.netty:netty-codec-http2
Exploitation
High exploitation probability; assess promptly
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Netty是Netty社区的一款非阻塞I/O客户端-服务器框架，它主要用于开发Java网络应用程序，如协议服务器和客户端等。 Netty 存在环境问题漏洞，该漏洞源于请求以HTTP 2流的形式传入，则被转换为HTTP 1.1对象。

CVSS 5.9 · Medium EPSS 18.89% · P97

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application
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I. Basic Information for CVE-2021-21295

Vulnerability Information
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Vulnerability Title
Possible request smuggling in HTTP/2 due missing validation
Source: CVE Program / CVE List V5
Vulnerability Description
Netty is an open-source, asynchronous event-driven network application framework for rapid development of maintainable high performance protocol servers & clients. In Netty (io.netty:netty-codec-http2) before version 4.1.60.Final there is a vulnerability that enables request smuggling. If a Content-Length header is present in the original HTTP/2 request, the field is not validated by `Http2MultiplexHandler` as it is propagated up. This is fine as long as the request is not proxied through as HTTP/1.1. If the request comes in as an HTTP/2 stream, gets converted into the HTTP/1.1 domain objects (`HttpRequest`, `HttpContent`, etc.) via `Http2StreamFrameToHttpObjectCodec `and then sent up to the child channel's pipeline and proxied through a remote peer as HTTP/1.1 this may result in request smuggling. In a proxy case, users may assume the content-length is validated somehow, which is not the case. If the request is forwarded to a backend channel that is a HTTP/1.1 connection, the Content-Length now has meaning and needs to be checked. An attacker can smuggle requests inside the body as it gets downgraded from HTTP/2 to HTTP/1.1. For an example attack refer to the linked GitHub Advisory. Users are only affected if all of this is true: `HTTP2MultiplexCodec` or `Http2FrameCodec` is used, `Http2StreamFrameToHttpObjectCodec` is used to convert to HTTP/1.1 objects, and these HTTP/1.1 objects are forwarded to another remote peer. This has been patched in 4.1.60.Final As a workaround, the user can do the validation by themselves by implementing a custom `ChannelInboundHandler` that is put in the `ChannelPipeline` behind `Http2StreamFrameToHttpObjectCodec`.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
HTTP请求的解释不一致性(HTTP请求私运)
Source: CVE Program / CVE List V5
Vulnerability Title
Netty 环境问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Netty是Netty社区的一款非阻塞I/O客户端-服务器框架，它主要用于开发Java网络应用程序，如协议服务器和客户端等。 Netty 存在环境问题漏洞，该漏洞源于请求以HTTP 2流的形式传入，则被转换为HTTP 1.1对象。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
netty io.netty:netty-codec-http2 < 4.1.60.Final -

II. Public POCs for CVE-2021-21295

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III. Intelligence Information for CVE-2021-21295

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Patches & Fixes for CVE-2021-21295 (2)

Vendor Advisories for CVE-2021-21295 (4)

Mailing List Discussions for CVE-2021-21295 (83)

IV. Related Vulnerabilities

Same vendor: netty
Same weakness: CWE-444

V. Comments for CVE-2021-21295

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