In particular, following 4 issues are related to to tightvnc viewer:
```
1. global buffer overflow in corre.c
In `vnc_unixsrc/vncviewer/corre.c` inside the `HandleCoRREBPP` function
global buffer overflow occurs due to the lack of size check.
`buffer` is defined in rfbproto.c:96 as ```char buffer[640*480];```. Inside
`HandleCoRREBPP` function data is being read to the buffer
`ReadFromRFBServer(buffer, hdr.nSubrects * (4 + (BPP / 8))` where
`hdr.nSubrects` is 32-bit unsigned integer controlled by remote user.
2. heap buffer overflow in rfbServerCutText handler
Heap buffer overflow in `rfbServerCutText` handler inside
`HandleRFBServerMessage` happens due to the malloc argument unsigned integer
overflow on line rfbproto.c:1220. Suppose msg.sct.length equals 0xffffffff,
then `malloc(msg.sct.length+1);` = `malloc(0);` will allocate small heap chunk
of size 0x10. But `msg.sct.length` = 0xffffffff bytes may be read in this chunk
on line 1222 (`ReadFromRFBServer(serverCutText, msg.sct.length)`).
3. heap buffer overflow in InitialiseRFBConnection function
Heap buffer overflow `InitialiseRFBConnection` function happens due to the
malloc argument unsigned integer overflow on line rfbproto.c:307. Because of
the integer overflow `malloc` function will allocate small heap chunk of size
0x10 and 0xffffffff bytes will be read into the chunk by ReadFromRFBServer
function.
4. null-ptr dereference in `zlib.c`
Because malloc result is not checked after allocation on line zlib.c:56
null pointer dereference is possible if malloc argument is too big and malloc
fill fail to allocate memory Allocation of raw buffer : `raw_buffer = (char*)
malloc( raw_buffer_size );`, next usage of raw_buffer is on line 68
```
P.S. As stated in the same thread of the mailing list by Solar Designer
tightvnc (as well as libvnc) suffers from user completely controlling
size of allocation, which may lead to resource exhaustion, and also
LibVNC fix by casting to (uint64_t) seems to be insufficient, because
malloc() has size_t argument and issue will remain on 32-bit platforms.
So proper allocation limiting is required to completely fix this issue.
** Tags added: security
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https://bugs.launchpad.net/bugs/1808989
Title:
tightvnc vulnerabilities
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