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net/http/cgi,net/http/fcgi: Cross-Site Scripting (XSS) when Content-Type is not specified #40928

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empijei opened this issue Aug 20, 2020 · 6 comments
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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done. release-blocker Security
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@empijei
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empijei commented Aug 20, 2020

When a Handler does not explicitly set the Content-Type header, both CGI implementations default to “text/html”.

If an attacker can make a server generate content under their control (e.g. a JSON containing user data or an uploaded image file) this might be mistakenly returned by the server as “text/html”. If a victim visits such a page they could get the attacker's code executed in the context of the server origin.

After the fix, the Content-Type header is set based on the contents of the first Write using http.DetectContentType, which is consistent with the behavior of the net/http package.

Although this protects some applications that validate the contents of uploaded files, not setting the Content-Type header explicitly on any attacker-controlled file is unsafe and should be avoided.

Thanks to RedTeam Pentesting GmbH for reporting this issue, you can access their advisory at the following address once it's published: https://www.redteam-pentesting.de/advisories/rt-sa-2020-004

This issue is CVE-2020-24553.

@dmitshur dmitshur added the WaitingForInfo Issue is not actionable because of missing required information, which needs to be provided. label Aug 21, 2020
@FiloSottile FiloSottile added Security and removed WaitingForInfo Issue is not actionable because of missing required information, which needs to be provided. labels Sep 1, 2020
@FiloSottile FiloSottile added this to the Go1.16 milestone Sep 1, 2020
@FiloSottile FiloSottile changed the title Taking this issue ID net/http/cgi,net/http/fcgi: Cross-Site Scripting (XSS) when Content-Type is not specified Sep 1, 2020
@dmitshur dmitshur added the NeedsFix The path to resolution is known, but the work has not been done. label Sep 1, 2020
@gopherbot
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Change https://golang.org/cl/252179 mentions this issue: net/http/cgi,net/http/fcgi: add Content-Type detection

@rtpt-alexanderneumann
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Our advisory has been published: https://www.redteam-pentesting.de/advisories/rt-sa-2020-004

@toothrot
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/cc @FiloSottile @katiehockman @empijei

@katiehockman
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Huh. This should have been closed by https://go-review.googlesource.com/c/go/+/252179, which includes Fixes #40928. Apparently our tooling didn't pick it up for some reason.

In any case, this has been resolved.

@katiehockman
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My bad, that CL hasn't been merged yet. Re-opening.

@katiehockman katiehockman reopened this Sep 10, 2020
@dmitshur
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This issue was open because CL 252179 has not been submitted yet. I'll reopen to track that (otherwise we risk shipping Go 1.16 without the fix).

I left a ping comment on the CL.

@golang golang locked and limited conversation to collaborators Sep 14, 2021
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