All,
I've been doing some reading about the recently-publicized Big-IP
vulnerability and I was wondering if httpd is doing the right thing.
According to Randori's analysis[1] of the flaw, there is confusion
between Apache httpd and Jetty (introduced by Big-IP) as to which
component is responsible for authentication and authorization.
The root of the problem is that they have two different authentication
mechanisms for different types of users. It's possible to send a request
that tells Apache httpd "I will be authenticated by Jetty" and by the
tie the request gets to Jetty it says "I've already been authenticated".
This is done using some headers:
Authorization: Basic YWRtaW46
X-F5-Auth-Token: 1
Connection: X-Forwarded-Host, X-F5-Auth-Token
Big-IP uses the X-F5-Auth-Token to tell httpd that Jetty will
authenticate the request, so it proxies the request through to Jetty.
But the Connection header causes httpd to strip-out the X-F5-Auth-Token
header as it's being proxied and then Jetty makes a bad decision with
the Authorization header.
But I'm wondering about why httpd removes that X-F5-Auth-Token header.
RC 2616[1] says that the Connection header contains headers to remove
from proxied connections, but:
"
Message headers listed in the Connection header MUST NOT include
end-to-end headers, such as Cache-Control.
"
Section 13.5.1[3] defines hop-by-hop and end-to-end headers:
"
The following HTTP/1.1 headers are hop-by-hop headers:
- Connection
- Keep-Alive
- Proxy-Authenticate
- Proxy-Authorization
- TE
- Trailers
- Transfer-Encoding
- Upgrade
All other headers defined by HTTP/1.1 are end-to-end headers.
"
Given the above, I believe the interpretation of X-F5-Auth-Token should
be that it is an end-to-end header, and should therefore NOT be removed
from the proxied request.
The text does say "All other headers *defined by HTTP/1.1* are
end-to-end headers" (emphasis mine, of course), and the X-F5-Auth-Token
header isn't defined by HTTP/1.1 (it's a custom one), but I think the
definition of specific hop-by-hop headers implies that *all* other
headers should be considered end-to-end.
Have I missed something in my reading of the spec, or the vulnerability
report itself?
-chris
[1] https://www.randori.com/blog/vulnerability-analysis-cve-2022-1388/
[2] https://datatracker.ietf.org/doc/html/rfc2616#section-14.10
[3] https://datatracker.ietf.org/doc/html/rfc2616#section-13.5.1
I've been doing some reading about the recently-publicized Big-IP
vulnerability and I was wondering if httpd is doing the right thing.
According to Randori's analysis[1] of the flaw, there is confusion
between Apache httpd and Jetty (introduced by Big-IP) as to which
component is responsible for authentication and authorization.
The root of the problem is that they have two different authentication
mechanisms for different types of users. It's possible to send a request
that tells Apache httpd "I will be authenticated by Jetty" and by the
tie the request gets to Jetty it says "I've already been authenticated".
This is done using some headers:
Authorization: Basic YWRtaW46
X-F5-Auth-Token: 1
Connection: X-Forwarded-Host, X-F5-Auth-Token
Big-IP uses the X-F5-Auth-Token to tell httpd that Jetty will
authenticate the request, so it proxies the request through to Jetty.
But the Connection header causes httpd to strip-out the X-F5-Auth-Token
header as it's being proxied and then Jetty makes a bad decision with
the Authorization header.
But I'm wondering about why httpd removes that X-F5-Auth-Token header.
RC 2616[1] says that the Connection header contains headers to remove
from proxied connections, but:
"
Message headers listed in the Connection header MUST NOT include
end-to-end headers, such as Cache-Control.
"
Section 13.5.1[3] defines hop-by-hop and end-to-end headers:
"
The following HTTP/1.1 headers are hop-by-hop headers:
- Connection
- Keep-Alive
- Proxy-Authenticate
- Proxy-Authorization
- TE
- Trailers
- Transfer-Encoding
- Upgrade
All other headers defined by HTTP/1.1 are end-to-end headers.
"
Given the above, I believe the interpretation of X-F5-Auth-Token should
be that it is an end-to-end header, and should therefore NOT be removed
from the proxied request.
The text does say "All other headers *defined by HTTP/1.1* are
end-to-end headers" (emphasis mine, of course), and the X-F5-Auth-Token
header isn't defined by HTTP/1.1 (it's a custom one), but I think the
definition of specific hop-by-hop headers implies that *all* other
headers should be considered end-to-end.
Have I missed something in my reading of the spec, or the vulnerability
report itself?
-chris
[1] https://www.randori.com/blog/vulnerability-analysis-cve-2022-1388/
[2] https://datatracker.ietf.org/doc/html/rfc2616#section-14.10
[3] https://datatracker.ietf.org/doc/html/rfc2616#section-13.5.1