CVE Request: UnRTF: stack-based buffer overflows in cmd_* functions

[Salvatore Bonaccorso <carnil () debian org>]

Hi

As reported by "Skylake" in the Debian bugtracker[1], UnRTF is prone
to stack-based buffer overflows in various cmd_* functions.

> I've found a Stack-based buffer overflow in unrtf 0.21.9, which
> affects three functions including: cmd_expand, cmd_emboss and
> cmd_engrave.
>
> # convert.c
>
> static int
> cmd_expand (Word *w, int align, char has_param, int param) {
> char str[10];
> if (has_param) {
> sprintf(str, "%d", param/4); // Overflow, 9-digit negative value triggers the bug
> if (!param)
> attr_pop(ATTR_EXPAND);
> else
> attr_push(ATTR_EXPAND, str);
> }
> return FALSE;
> }
>
> Apparently writing a negative integer to the buffer can trigger the
> overflow (Minus sign needs an extra byte).
>
> * How to trigger the bug *
>
> $ echo "\expnd-400000000" > poc
> $ unrtf poc

A preliminary patch can be found in the Debian bugtracker, but it is
not yet finalized.

Could you assign (a?) CVE as needed? Does one CVE suffice here, since
same class of issue in various cmd_* functions from one reporter?
Whilest, at least in Debian, unrtf is compiled with FORTIFY_SOURCE=2
and the buffer overflows are detected, at least if any exposed
application uses unrtf to process untrusted input, this might lead to
a denial-of-service.

 [1] https://bugs.debian.org/849705

Regards,
Salvatore