Opened 4 years ago

Last modified 4 years ago

#2191 closed defect

Nginx doesn't escape unsafe characters on proxying — at Initial Version

Reported by: ZigzagAK@… Owned by:
Priority: major Milestone:
Component: nginx-core Version: 1.19.x
Keywords: Cc:
uname -a:
nginx -V: nginx version: nginx/1.19.6
built by gcc 7.3.1 20180303 (Red Hat 7.3.1-5) (GCC)
built with OpenSSL 1.0.2k-fips 26 Jan 2017
TLS SNI support enabled
configure arguments: --prefix=/root/tmp/nginx-1.19.6 --with-http_v2_module --with-poll_module --with-threads --with-file-aio --with-pcre-jit --with-http_stub_status_module --with-http_ssl_module --with-stream_ssl_module --with-stream_ssl_preread_module --with-stream --with-http_auth_request_module --with-http_realip_module --with-http_gunzip_module --with-http_sub_module

Description

Example synthetic configuration:

upstream xxxx {
  server 127.0.0.1:3456;
}

server {
  listen 3456;
  location / {
    return 200 '$uri\n$request\n';
  }
}

server {
  listen 2345;
  location / {
    rewrite ^ $uri break;
    proxy_pass http://xxxx;
  }
}

[root@e078281ef0c9 gateway]# curl localhost:3456/xxx/aaa%3C%3E%22
/xxx/aaa<>"
GET /xxx/aaa%3C%3E%22 HTTP/1.1
[root@e078281ef0c9 gateway]# curl localhost:2345/xxx/aaa%3C%3E%22
/xxx/aaa<>"
GET /xxx/aaa<>" HTTP/1.1
[root@e078281ef0c9 gateway]#

tcpdump:

before nginx:

GET /xxx/aaa%3C%3E%22 HTTP/1.1
User-Agent: curl/7.29.0
Host: localhost:2345
Accept: */*

after nginx:

GET /xxx/aaa<>" HTTP/1.1
Connection: keep-alive
Host: localhost:2345
Connection: keep-alive
User-Agent: curl/7.29.0
Accept: */*
X-Forwarded-For: 127.0.0.1
X-Real-IP: 127.0.0.1

​https://datatracker.ietf.org/doc/html/rfc1738#section-2.2

... The characters "<" and ">" are unsafe because they are used as the

delimiters around URLs in free text; the quote mark (""") is used to
delimit URLs in some systems.

All unsafe characters must always be encoded within a URL.

Cause: ​https://github.com/nginx/nginx/blob/master/src/core/ngx_string.c#L1496

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