From 2105dae0f9d7a964375ce681e53cb165375f84c1 Mon Sep 17 00:00:00 2001
From: Glenn Strauss <gstrauss@gluelogic.com>
Date: Sun, 1 Jul 2018 12:38:28 -0400
Subject: [PATCH] [mod_alias] security: potential path traversal with specific
 configs

Security: potential path traversal of a single directory above the alias
target with a specific mod_alias config where the alias which is matched
does not end in '/', but alias target filesystem path does end in '/'.

e.g. server.docroot = "/srv/www/host/HOSTNAME/docroot"
     alias.url = ( "/img" => "/srv/www/hosts/HOSTNAME/images/" )

If a malicious URL "/img../" were passed, the request would be
for directory "/srv/www/hosts/HOSTNAME/images/../" which would resolve
to "/srv/www/hosts/HOSTNAME/".  If mod_dirlisting were enabled, which
is not the default, this would result in listing the contents of the
directory above the alias.  An attacker might also try to directly
access files anywhere under that path, which is one level above the
intended aliased path.

credit: Orange Tsai(@orange_8361) from DEVCORE
---
 src/mod_alias.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

Index: lighttpd/src/mod_alias.c
===================================================================
--- lighttpd.orig/src/mod_alias.c
+++ lighttpd/src/mod_alias.c
@@ -176,6 +176,21 @@ PHYSICALPATH_FUNC(mod_alias_physical_han
 					strncmp(uri_ptr, ds->key->ptr, alias_len))) {
 			/* matched */
 
+			/* check for path traversal in url-path following alias if key
+			 * does not end in slash, but replacement value ends in slash */
+			if (uri_ptr[alias_len] == '.') {
+				char *s = uri_ptr + alias_len + 1;
+				if (*s == '.') ++s;
+				if (*s == '/' || *s == '\0') {
+					size_t vlen = buffer_string_length(ds->value);
+					if (0 != alias_len && ds->key->ptr[alias_len-1] != '/'
+					    && 0 != vlen && ds->value->ptr[vlen-1] == '/') {
+						con->http_status = 403;
+						return HANDLER_FINISHED;
+					}
+				}
+			}
+
 			buffer_copy_buffer(con->physical.basedir, ds->value);
 			buffer_copy_buffer(srv->tmp_buf, ds->value);
 			buffer_append_string(srv->tmp_buf, uri_ptr + alias_len);
