Extended ClientCutText messages start with a 4-byte header. If len < 4,
an integer underflow occurs in vnc_client_cut_text_ext. The result is
used to decompress data in a while loop in inflate_buffer, leading to
CPU consumption and denial of service. Prevent this by checking dlen in
protocol_client_msg.
Fixes: CVE-2022-3165
Fixes: 0bf41cab93e5 ("ui/vnc: clipboard support")
Reported-by: TangPeng <[email protected]>
Signed-off-by: Mauro Matteo Cascella <[email protected]>
---
Extended Clipboard Pseudo-Encoding:
https://github.com/rfbproto/rfbproto/blob/master/rfbproto.rst#extended-clipboard-pseudo-encoding
ui/vnc.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/ui/vnc.c b/ui/vnc.c
index 6a05d06147..acb3629cd8 100644
--- a/ui/vnc.c
+++ b/ui/vnc.c
@@ -2442,8 +2442,8 @@ static int protocol_client_msg(VncState *vs, uint8_t
*data, size_t len)
if (len == 1) {
return 8;
}
+ uint32_t dlen = abs(read_s32(data, 4));
if (len == 8) {
- uint32_t dlen = abs(read_s32(data, 4));
if (dlen > (1 << 20)) {
error_report("vnc: client_cut_text msg payload has %u bytes"
" which exceeds our limit of 1MB.", dlen);
@@ -2456,8 +2456,13 @@ static int protocol_client_msg(VncState *vs, uint8_t
*data, size_t len)
}
if (read_s32(data, 4) < 0) {
- vnc_client_cut_text_ext(vs, abs(read_s32(data, 4)),
- read_u32(data, 8), data + 12);
+ if (dlen < 4) {
+ error_report("vnc: malformed payload (header less than 4
bytes)"
+ " in extended clipboard pseudo-encoding.");
+ vnc_client_error(vs);
+ break;
+ }
+ vnc_client_cut_text_ext(vs, dlen, read_u32(data, 8), data + 12);
break;
}
vnc_client_cut_text(vs, read_u32(data, 4), data + 8);
--
2.37.3
