>From 53e400e4e8d88b76b8d05a9ce53f4306f03d8860 Mon Sep 17 00:00:00 2001
From: Oswald Buddenhagen <ossi@users.sf.net>
Date: Sun, 14 Feb 2021 20:42:37 +0100
Subject: [PATCH] CVE-2021-20247: reject funny mailbox names from IMAP LIST/LSUB
in particular, '..' in the name could be used to escape the Path/Inbox
of a Maildir Store, which could be exploited for stealing or deleting
data, or staging a (mild) DoS attack.
---
src/drv_imap.c | 30 +++++++++++++++++++++++++++++-
1 file changed, 29 insertions(+), 1 deletion(-)
diff --git a/src/drv_imap.c b/src/drv_imap.c
index e6e4b26..f18500d 100644
--- a/src/drv_imap.c
+++ b/src/drv_imap.c
@@ -1378,7 +1378,7 @@ static int
parse_list_rsp_p2( imap_store_t *ctx, list_t *list, char *cmd ATTR_UNUSED )
{
string_list_t *narg;
- char *arg;
+ char *arg, c;
int argl;
uint l;
@@ -1422,6 +1422,34 @@ parse_list_rsp_p2( imap_store_t *ctx, list_t *list, char *cmd ATTR_UNUSED )
warn( "IMAP warning: ignoring mailbox %s (reserved character '/' in name)\n", arg );
return LIST_OK;
}
+ // Validate the normalized name. Technically speaking, we could tolerate
+ // '//' and '/./', and '/../' being forbidden is a limitation of the Maildir
+ // driver, but there isn't really a legitimate reason for these being present.
+ for (const char *p = narg->string, *sp = p;;) {
+ if (!(c = *p) || c == '/') {
+ uint pcl = (uint)(p - sp);
+ if (!pcl) {
+ error( "IMAP warning: ignoring mailbox '%s' due to empty name component\n", narg->string );
+ free( narg );
+ return LIST_OK;
+ }
+ if (pcl == 1 && sp[0] == '.') {
+ error( "IMAP warning: ignoring mailbox '%s' due to '.' component\n", narg->string );
+ free( narg );
+ return LIST_OK;
+ }
+ if (pcl == 2 && sp[0] == '.' && sp[1] == '.') {
+ error( "IMAP error: LIST'd mailbox name '%s' contains '..' component - THIS MIGHT BE AN ATTEMPT TO HACK YOU!\n", narg->string );
+ free( narg );
+ return LIST_BAD;
+ }
+ if (!c)
+ break;
+ sp = ++p;
+ } else {
+ ++p;
+ }
+ }
narg->next = ctx->boxes;
ctx->boxes = narg;
return LIST_OK;
--
2.29.2.2.g268056bf11.dirty