CVE-2023-40225 (Other, published 2023-08-10T21:15Z)
Description: value: HAProxy through 2.0.32, 2.1.x and 2.2.x through 2.2.30, 2.3.x and 2.4.x through 2.4.23, 2.5.x and 2.6.x before 2.6.15, 2.7.x before 2.7.10, and 2.8.x before 2.8.2 forwards empty Content-Length headers, violating RFC 9110 section 8.6. In uncommon cases, an HTTP/1 server behind HAProxy may interpret the payload as an extra request.
Severity: nan (CVSS v3 base score: 7.2)
Weakness: CWE-444 \u2014 Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
The product acts as an intermediary HTTP agent
         (such as a proxy or firewall) in the data flow between two
         entities such as a client and server, but it does not
         interpret malformed HTTP requests or responses in ways that
         are consistent with how the messages will be processed by
         those entities that are at the ultimate destination.
Repository: https://github.com/haproxy/haproxy
Files changed:
reg-tests/http-messaging/h1_to_h1.vtc
reg-tests/http-messaging/h2_to_h1.vtc
src/h1.c
src/http.c
Commit message: BUG/MAJOR: http: reject any empty content-length header value

The content-length header parser has its dedicated function, in order
to take extreme care about invalid, unparsable, or conflicting values.
But there's a corner case in it, by which it stops comparing values
when reaching the end of the header. This has for a side effect that
an empty value or a value that ends with a comma does not deserve
further analysis, and it acts as if the header was absent.

While this is not necessarily a problem for the value ending with a
comma as it will be cause a header folding and will disappear, it is a
problem for the first isolated empty header because this one will not
be recontructed when next ones are seen, and will be passed as-is to the
backend server. A vulnerable HTTP/1 server hosted behind haproxy that
would just use this first value as "0" and ignore the valid one would
then not be protected by haproxy and could be attacked this way, taking
the payload for an extra request.

In field the risk depends on the server. Most commonly used servers
already have safe content-length parsers, but users relying on haproxy
to protect a known-vulnerable server might be at risk (and the risk of
a bug even in a reputable server should never be dismissed).

A configuration-based work-around consists in adding the following rule
in the frontend, to explicitly reject requests featuring an empty
content-length header that would have not be folded into an existing
one:

    http-request deny if { hdr_len(content-length) 0 }

The real fix consists in adjusting the parser so that it always expects a
value at the beginning of the header or after a comma. It will now reject
requests and responses having empty values anywhere in the C-L header.

This needs to be backported to all supported versions. Note that the
modification was made to functions h1_parse_cont_len_header() and
http_parse_cont_len_header(). Prior to 2.8 the latter was in
h2_parse_cont_len_header(). One day the two should be refused but the
former is also used by Lua.

The HTTP messaging reg-tests were completed to test these cases.

Thanks to Ben Kallus of Dartmouth College and Narf Industries for
reporting this! (this is in GH #2237).


Vulnerable code:
	word.ptr = value->ptr - 1; // -1 for next loop's pre-increment
	while (++word.ptr < e) {
		if (unlikely(HTTP_IS_LWS(*word.ptr)))
	word.ptr = value->ptr - 1; // -1 for next loop's pre-increment
	while (++word.ptr < e) {
		if (unlikely(HTTP_IS_LWS(*word.ptr)))

Fixed code:

client c4h1 -connect ${h1_feh1_sock} {
	# this request is invalid and advertises an invalid C-L ending with an
        # empty value, which results in a stream error.
	txreq \
	  -req "GET" \
	  -url "/test31.html" \
          -hdr "content-length: 0," \
          -hdr "connection: close"
	rxresp
	expect resp.status == 400
	expect_close
} -run

client c5h1 -connect ${h1_feh1_sock} {
	# this request is invalid and advertises an empty C-L, which results
	# in a stream error.
	txreq \
	  -req "GET" \
	  -url "/test41.html" \
          -hdr "content-length:" \
          -hdr "connection: close"
	rxresp
	expect resp.status == 400
	expect_close
} -run
barrier b5 cond 2 -cyclic
barrier b6 cond 2 -cyclic

	barrier b5 sync
	# the next request is never received

	barrier b6 sync
	# the next request is never received

	# fifth request is invalid and advertises an invalid C-L ending with an
        # empty value, which results in a stream error.
	stream 9 {
		barrier b5 sync
		txreq \
		  -req "GET" \
		  -scheme "https" \
		  -url "/test5.html" \
		  -hdr "content-length" "0," \
		  -nostrend
		rxrst
	} -run

	# sixth request is invalid and advertises an empty C-L, which results
	# in a stream error.
	stream 11 {
		barrier b6 sync
		txreq \
		  -req "GET" \
		  -scheme "https" \
		  -url "/test6.html" \
		  -hdr "content-length" "" \
		  -nostrend
		rxrst
	} -run

	# fifth request is invalid and advertises invalid C-L ending with an
        # empty value, which results in a stream error.
	stream 9 {
		barrier b5 sync
		txreq \
		  -req "POST" \
		  -scheme "https" \
		  -url "/test25.html" \
		  -hdr "content-length" "0," \
		  -nostrend
		rxrst
	} -run

	# sixth request is invalid and advertises an empty C-L, which results
	# in a stream error.
	stream 11 {
		barrier b6 sync
		txreq \
		  -req "POST" \
		  -scheme "https" \
		  -url "/test26.html" \
		  -hdr "content-length" "" \
		  -nostrend
		rxrst
	} -run
	word.ptr = value->ptr;
	while (1) {
		if (word.ptr >= e) {
			/* empty header or empty value */
			goto fail;
		}

		if (unlikely(HTTP_IS_LWS(*word.ptr))) {
			word.ptr++;
		}

		/* Now either n==e and we're done, or n points to the comma,
		 * and we skip it and continue.
		 */
		if (n++ == e)
			break;

	word.ptr = value->ptr;
	while (1) {
		if (word.ptr >= e) {
			/* empty header or empty value */
			goto fail;
		}

		if (unlikely(HTTP_IS_LWS(*word.ptr))) {
			word.ptr++;
		}

		/* Now either n==e and we're done, or n points to the comma,
		 * and we skip it and continue.
		 */
		if (n++ == e)
			break;