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osvGoogleOSV:GHSA-WM47-8V5P-WJPJ
HistoryMar 09, 2021 - 6:49 p.m.

Possible request smuggling in HTTP/2 due missing validation

2021-03-0918:49:49
Google
osv.dev
55

5.9 Medium

CVSS3

Attack Vector

NETWORK

Attack Complexity

HIGH

Privileges Required

NONE

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

NONE

Integrity Impact

HIGH

Availability Impact

NONE

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

4.3 Medium

CVSS2

Access Vector

NETWORK

Access Complexity

MEDIUM

Authentication

NONE

Confidentiality Impact

NONE

Integrity Impact

PARTIAL

Availability Impact

NONE

AV:N/AC:M/Au:N/C:N/I:P/A:N

0.184 Low

EPSS

Percentile

96.1%

Impact

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. A sample attack request looks like:

POST / HTTP/2
:authority:: externaldomain.com
Content-Length: 4

asdfGET /evilRedirect HTTP/1.1
Host: internaldomain.com

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
  • These HTTP/1.1 objects are forwarded to another remote peer.

Patches

This has been patched in 4.1.60.Final

Workarounds

The user can do the validation by themselves by implementing a custom ChannelInboundHandler that is put in the ChannelPipeline behind Http2StreamFrameToHttpObjectCodec.

References

Related change to workaround the problem: https://github.com/Netflix/zuul/pull/980

References

5.9 Medium

CVSS3

Attack Vector

NETWORK

Attack Complexity

HIGH

Privileges Required

NONE

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

NONE

Integrity Impact

HIGH

Availability Impact

NONE

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

4.3 Medium

CVSS2

Access Vector

NETWORK

Access Complexity

MEDIUM

Authentication

NONE

Confidentiality Impact

NONE

Integrity Impact

PARTIAL

Availability Impact

NONE

AV:N/AC:M/Au:N/C:N/I:P/A:N

0.184 Low

EPSS

Percentile

96.1%