Multiple Host header values handled poorly #8716

joakime · 2022-10-14T16:51:06Z

Jetty version(s)
9.4.x thru 12.0.x

Java version/vendor (use: java -version)
All

OS type/version
All

Description
When a request is received with multiple host headers it's handled poorly.

This was pointed out by @Hexcles at #7278 (comment)

Example using the jetty 11 demos.

$ curl -vvvv -H"Host: localhost, foo, bar, zed" http://localhost:8080/test/dump/info
*   Trying 127.0.0.1:8080...
* Connected to localhost (127.0.0.1) port 8080 (#0)
> GET /test/dump/info HTTP/1.1
> Host: localhost, foo, bar, zed
> User-Agent: curl/7.81.0
> Accept: */*
> 
* Mark bundle as not supporting multiuse
< HTTP/1.1 200 OK
< Set-Cookie: visited=yes
< Expires: Thu, 01 Jan 1970 00:00:00 GMT
< Set-Cookie: JSESSIONID=node013ntsnazjuutz1gpikvehddsnk1.node0; Path=/test
< Content-Type: text/html;charset=utf-8
< Vary: Accept-Encoding
< Content-Length: 10477
< Server: Jetty(11.0.11)
< 
<html>
<body>
<h1>Dump Servlet</h1>
...(snip)...
<th align="right">getRequestURI:&nbsp;</th><td>/test/dump/info</td></tr><tr>
<th align="right">getRequestURL:&nbsp;</th><td>http://localhost, foo, bar, zed/test/dump/info</td></tr><tr>
<th align="right">getScheme:&nbsp;</th><td>http</td></tr><tr>
<th align="right">getServerName:&nbsp;</th><td>localhost, foo, bar, zed</td></tr><tr>
...(snip)...

So the key bits in the above example are ...

HTTP/1.1 was used
The request header Host: localhost, foo, bar, zed was sent
Jetty parsed it without error, and it resulted in odd API behavior
- HttpServletRequest.getRequestURL() is http://localhost, foo, bar, zed/test/dump/info
- HttpServletRequest.getServerName() is localhost, foo, bar, zed

The text was updated successfully, but these errors were encountered:

joakime · 2022-10-14T16:53:59Z

Looks like Jetty interprets the all field values, including commas, as a single "Host" (or Server Name), complete with commas.

Hexcles · 2022-10-14T17:15:14Z

Oh a minor correction: it's not multiple Host values that I encountered (I'm not sure if you're supposed to split Host value by commas like other headers), but multiple Host`` headers. You can't produce such a malformed request using curl, but you can use netcat: https://blog.shalvah.me/posts/fixing-the-host-header-vulnerability-with-nginx#:~:text=a%20custom%20middleware.-,Appendix,-If%20you%27re%20interested

https://httpwg.org/specs/rfc9112.html#request.target

A server MUST respond with a 400 (Bad Request) status code to any HTTP/1.1 request message that lacks a Host header field and to any request message that contains more than one Host header field line or a Host header field with an invalid field value.

joakime · 2022-10-14T19:00:42Z

We might want to revive the closed PR #7279 as it addressed many of the "bad host" and "bad authority" cases. (just not the multiple header cases)

Signed-off-by: Joakim Erdfelt <[email protected]>

joakime · 2022-10-14T19:10:33Z

Opened PR #8717 as a simple way to address this

Signed-off-by: Joakim Erdfelt <[email protected]>

* Issue #8716 - Handle bad host/authority headers better * Remove extra `Host` header in testcase that doesn't deal with bad Host headers * Create URIUtil.isRegName * Correcting HostPortTest.testValidAuthority * Correcting RequestTest.testInvalidHostHeader * Remove clonable, set to final Signed-off-by: Joakim Erdfelt <[email protected]>

joakime · 2022-12-01T22:50:24Z

Closing, as PR #8717 is merged.

bjorncs · 2023-01-18T12:11:52Z

Will Jetty issue a security advisory for the previous behaviour for accepting multiple Host headers? Jetty was susceptible of Host header injection attacks when combined with a load balancer / reverse proxy accepting multiple Host headers, as outlined in #7278 (comment).

joakime · 2023-01-18T14:29:59Z

@bjorncs please explain how accepting the last Host header is a security advisory?

joakime · 2023-01-18T14:37:39Z

@bjorncs there's a few variations of this ...

Variation 1: Duplicate headers, same value

GET /foo HTTP/1.1
Host: machine.com
Host: machine.com
Connection: close

This variation is rejected by the HttpParser.

Variation 2: Duplicate headers, different values

GET /foo HTTP/1.1
Host: machine.com
Host: example.org
Connection: close

This variation is rejected by the HttpParser.

Variation 3: Single header, comma delimited, with space, same value

GET /foo HTTP/1.1
Host: machine.com, machine.com
Connection: close

As the parsing of the Host header is not ever delimited, this is viewed a single authority.
HostPort will reject this due to the space character.

Variation 4: Single header, comma delimited, with space, different values

GET /foo HTTP/1.1
Host: machine.com, example.org
Connection: close

As the parsing of the Host header is not ever delimited, this is viewed a single authority.
HostPort will reject this due to the space character.

Variation 5: Single Header, comma delimited, no space.

GET /foo HTTP/1.1
Host: machine.com,example.org
Connection: close

As the parsing of the Host header is not ever delimited, this is viewed a single authority.
HostPort will allow this due to the fact that comma is not an invalid character for an authority.

joakime · 2023-01-18T14:40:36Z

What does java support when it comes to the variations of multiple headers with a comma?

 jshell> new URI("http", "machine.com,example.org", "/", null, null)
$1 ==> http://machine.com,example.org/

jshell> new URI("http://machine.com,example.org/")
$2 ==> http://machine.com,example.org/

jshell> new URI("http://machine.com, example.org/")
|  Exception java.net.URISyntaxException: Illegal character in authority at index 7: http://machine.com, example.org/
|        at URI$Parser.fail (URI.java:2913)
|        at URI$Parser.parseAuthority (URI.java:3247)
|        at URI$Parser.parseHierarchical (URI.java:3158)
|        at URI$Parser.parse (URI.java:3114)
|        at URI.<init> (URI.java:600)
|        at (#4:1)

gregw · 2023-01-18T20:32:53Z

I tried to generate a CVSS score for this change, but the problem is that on it's own there is no affect - no change of scope, no loss of integrity, no loss of confidentiality, no loss of availability.... so the score is 0.0.

It's the kind of issue that needs another component in order to have consequences. I.e. if a front end policed some security policy based on the first host header and then jetty acted on the second host header, that would indeed be a security problem.
So perhaps that is a loss of integrity with high attack complexity? CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N That's a score of 3.1, so at least something we could make an advisory around.

bjorncs · 2023-01-20T08:58:09Z

@joakime
I have reproduced variation 2 on 9.4.49 and 11.0.12 using nc/openssl s_client with handwritten HTTP/1.1 request. Both instances results in 200 OK in our configuration of Jetty embedded.

I'll try to outline the hypothetical scenario from my previous comment.
Let's say Jetty is configured with two virtual hosts, public.api and internal.api.
The public.api virtual host serves handlers that should be accessible publicy through a reverse proxy. The internal.api virtual host serves handlers that should not be accessible from the reverse proxy.

I interpret @Hexles's comment as CDNs such as Cloudflare would route based on the value of the first Host header, while including both Host headers in the forwarded request.

GET /my/internal/api HTTP/1.1
Host: public.api
Host: internal.api
Connection: close

Could the above request access an internal handler/rest-API in this scenario?

@gregw Agree, it's a fair assessment that it's not worthy an advisory. A reverse proxy that's non-compliant with RFC-9112 is required, and relying on virtual hosts configuration as a security measure is unlikely. I have not verified whether claims regarding the CDNs' handling of Host headers are true.

Hexcles · 2023-01-22T01:12:33Z

It's easy to verify that scenario 2 does get through Cloudflare (routed by the first Host), but I'm not at work and can't reproduce/confirm that the second Host isn't dropped by Cloudflare. Nginx, on the other hand, rejects scenario 2 with 400.

There is another variant 6: Host inconsistent with the authority component in the target URI:

GET https://public.api/my/internal/api HTTP/1.1
Host: internal.api
Connection: close

This scenario gets past both Cloudflare and Nginx, and I'd be surprised if the Host header is dropped by either proxy in this case. I believe this Host header should be considered as an "invalid field value" and result in a 400, too, but that's a different story.

@bjorncs your idea about having a single Jetty with two virtual hosts is interesting, and might worth verifying. In my case, it was because of some application-level auth code that determines whether a request is internal by looking at the host (to see if it's using the private Kubernetes domain). In addition, our pentester used this trick to get past WAF to exploit the infamous log4j bug because of course host/URL is logged.

gregw · 2023-01-23T06:34:31Z

All,

I'm very happy for us to issue a security advisory on this. We were interpreting the host header contrary to the specification, which in some circumstances can definitely be a security issue. It's hard to characterize, but no harm at least advising people that if they are on an old jetty, they need to consider any checking/routing done by an intermediary that might interpret multiple host headers differently to jetty.

joakime · 2023-02-03T15:36:00Z

@bjorncs @Hexcles There's been 2 recent PRs in jetty-10.0.x (will be merged to jetty-11.0.x) that are related to these issues.

Configurable Unsafe Host Header Behaviors #9283
- Introduces optional configurables HttpCompliance.DUPLICATE_HOST_HEADERS and HttpCompliance.UNSAFE_HOST_HEADER
Introduce HttpCompliance.MISMATCHED_AUTHORITY #9312

Default is to reject with 400 Bad Request.

These Compliance modes exist allow a server to operate in an unsafe mode while they work with their clients to address their bad usages of HTTP.

joakime added the Bug For general bugs on Jetty side label Oct 14, 2022

joakime mentioned this issue Oct 14, 2022

Properly support HTTP/1.1 with non-http scheme absolute-uri and empty Host header #7278

Open

joakime changed the title ~~Multiple Host headers values treated poorly~~ Multiple Host header values handled poorly Oct 14, 2022

joakime added a commit that referenced this issue Oct 14, 2022

Issue #8716 - Handle bad host/authority headers better

d4a7439

Signed-off-by: Joakim Erdfelt <[email protected]>

joakime self-assigned this Oct 14, 2022

joakime added a commit that referenced this issue Oct 25, 2022

Issue #8716 - Updates from review

d183957

Signed-off-by: Joakim Erdfelt <[email protected]>

joakime closed this as completed Dec 1, 2022

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Multiple Host header values handled poorly #8716

Multiple Host header values handled poorly #8716

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Multiple Host header values handled poorly #8716

Multiple Host header values handled poorly #8716

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