commit fe5d59f8e3169944e57eb1c60155c9ebd4912d48
Author: Oswald Buddenhagen <[email protected]>
Date: Sun Feb 14 20:42:37 2021 +0100
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 | 31 ++++++++++++++++++++++++++++++-
1 file changed, 30 insertions(+), 1 deletion(-)
diff --git a/src/drv_imap.c b/src/drv_imap.c
index 810479e..fbe2fed 100644
--- a/src/drv_imap.c
+++ b/src/drv_imap.c
@@ -1258,11 +1258,12 @@ 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, l;
if (!is_atom( list )) {
error( "IMAP error: malformed LIST response\n" );
+ listbad:
free_list( list );
return LIST_BAD;
}
@@ -1302,6 +1303,34 @@ 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 );
goto skip;
}
+ // 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 );
+ goto skip;
+ }
+ if (pcl == 1 && sp[0] == '.') {
+ error( "IMAP warning: ignoring mailbox '%s' due
to '.' component\n", narg->string );
+ free( narg );
+ goto skip;
+ }
+ 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 );
+ goto listbad;
+ }
+ if (!c)
+ break;
+ sp = ++p;
+ } else {
+ ++p;
+ }
+ }
narg->next = ctx->boxes;
ctx->boxes = narg;
skip:
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