BUG/MAJOR: h2: enforce stricter syntax checks on the :method pseudo-header
Before HTX was introduced, all the HTTP request elements passed in
pseudo-headers fields were used to build an HTTP/1 request whose syntax
was then scrutinized by the HTTP/1 parser, leaving no room to inject
invalid characters.
While NUL, CR and LF are properly blocked, it is possible to inject
spaces in the method so that once translated to HTTP/1, fields are
shifted by one spcae, and a lenient HTTP/1 server could possibly be
fooled into using a part of the method as the URI. For example, the
following request:
H2 request
:method: "GET /admin? HTTP/1.1"
:path: "/static/images"
would become:
GET /admin? HTTP/1.1 /static/images HTTP/1.1
It's important to note that the resulting request is *not* valid, and
that in order for this to be a problem, it requires that this request
is delivered to an already vulnerable HTTP/1 server.
A workaround here is to reject malformed methods by placing this rule
in the frontend or backend, at least before leaving haproxy in H1:
http-request reject if { method -m reg [^A-Z0-9] }
Alternately H2 may be globally disabled by commenting out the "alpn"
directive on "bind" lines, and by rejecting H2 streams creation by
adding the following statement to the global section:
tune.h2.max-concurrent-streams 0
This patch adds a check for each character of the method to make sure
they belong to the ones permitted in a token, as mentioned in RFC7231#4.1.
This should be backported to versions 2.0 and above. For older versions
not having HTX_FL_PARSING_ERROR, a "goto fail" works as well as it
results in a protocol error at the stream level. Non-HTX versions are
safe because the resulting invalid request will be rejected by the
internal HTTP/1 parser.
Thanks to Tim Düsterhus for reporting that one.
(cherry picked from commit 89265224d314a056d77d974284802c1b8a0dc97f)
Signed-off-by: Willy Tarreau <w@1wt.eu>
diff --git a/src/h2.c b/src/h2.c
index b31ff93..280bbd7 100644
--- a/src/h2.c
+++ b/src/h2.c
@@ -328,6 +328,14 @@
flags |= HTX_SL_F_HAS_AUTHORITY;
}
+ /* The method is a non-empty token (RFC7231#4.1) */
+ if (!meth_sl.len)
+ goto fail;
+ for (i = 0; i < meth_sl.len; i++) {
+ if (!HTTP_IS_TOKEN(meth_sl.ptr[i]))
+ htx->flags |= HTX_FL_PARSING_ERROR;
+ }
+
/* make sure the final URI isn't empty. Note that 7540#8.1.2.3 states
* that :path must not be empty.
*/