CVE-2019-20372 (published 2020-01-09T21:15Z)

NGINX before 1.17.7, with certain error_page configurations, allows HTTP request smuggling, as demonstrated by the ability of an attacker to read unauthorized web pages in environments where NGINX is being fronted by a load balancer.

Severity: MEDIUM
CVSS v2 base score: 4.3 (AV:N/AC:M/Au:N/C:P/I:N/A:N)
CVSS v3 base score: 5.3, MEDIUM (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N)

Weakness information:
cwe_id: CWE-444
cwe_name: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
description: 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.
extended_description: 
	   HTTP requests or responses ("messages") can be
	   malformed or unexpected in ways that cause web servers or
	   clients to interpret the messages in different ways than
	   intermediary HTTP agents such as load balancers, reverse
	   proxies, web caching proxies, application firewalls,
	   etc. For example, an adversary may be able to add duplicate
	   or different header fields that a client or server might
	   interpret as one set of messages, whereas the intermediary
	   might interpret the same sequence of bytes as a different
	   set of messages. For example, discrepancies can arise in
	   how to handle duplicate headers like two Transfer-encoding
	   (TE) or two Content-length (CL), or the malicious HTTP
	   message will have different headers for TE and
	   CL.
	   The inconsistent parsing and interpretation of messages
	   can allow the adversary to "smuggle" a message to the
	   client/server without the intermediary being aware of it.
	   This weakness is usually the result of the usage
	   of outdated or incompatible HTTP protocol versions in the
	   HTTP agents.
         
         

Fix information:
repo_url: https://github.com/nginx/nginx
commit_details: repo_url: https://github.com/nginx/nginx
author: Ruslan Ermilov
author_date: 2019-12-23 15:45:46+03:00
msg: Discard request body when redirecting to a URL via error_page.

Reported by Bert JW Regeer and Francisco Oca Gonzalez.
repository: repo_url: https://github.com/nginx/nginx
repo_name: nginx/nginx
description: An official read-only mirror of http://hg.nginx.org/nginx/ which is updated hourly. Pull requests on GitHub cannot be accepted and will be automatically closed. The proper way to submit changes to nginx is via the nginx development mailing list, see http://nginx.org/en/docs/contributing_changes.html
repo_language: C
owner: nginx
file_changes: filename: ngx_http_special_response.c
change_type: ModificationType.MODIFY
diff: @@ -623,6 +623,12 @@ ngx_http_send_error_page(ngx_http_request_t *r, ngx_http_err_page_t *err_page)
         return ngx_http_named_location(r, &uri);
     }
 
+    r->expect_tested = 1;
+
+    if (ngx_http_discard_request_body(r) != NGX_OK) {
+        r->keepalive = 0;
+    }
+
     location = ngx_list_push(&r->headers_out.headers);
 
     if (location == NULL) {

programming_language: HTML