Very nice work Diego!
Is there a POC showing the overflow, as that would make writing unit tests easier?
Also is this vulnerability in the same class as other printf vulnerabilities, where it requires a developer to pass untrusted input as the format string to print?
Thank you! Linted
On Tue, Oct 24, 2023, 7:16 AM Diego Dias diego.dias@kernkonzept.com wrote:
Dear uclibc-ng developers,
We have run a static analysis tool (Klocwork) in uclibc and one of its checkers (ABV.GENERAL) indicates a potential buffer overflow in uclibc-ng/src/master/libc/stdio/_vfprintf.c:1045
The problem occurs as an out-of-bounds access to array 'argtype', which is a member of 'ppfs_t'. This array has length 'MAX_ARGS'. According to the static analysis tool, the array can be accessed using index 'n' of value '-1' and '9..254' in the conditional shown below:
// File: uclibc-ng/src/master/libc/stdio/_vfprintf.c:1045 if (_is_equal_or_bigger_arg(ppfs->argtype[n], argtype[i])) { ppfs->argtype[n] = argtype[i]; }
Triggering an out-of-bounds access for 'n=-1' is relatively simply when using printf or similar functions (e.g. vfprintf). Such out-of-bounds access occurs when positional arguments are specified, as in the following statement:
printf("%1$s", "Hello world!");
Although Klocwork claims that the array might be accessed using indexes '9..254', we were not able to trigger an out-of-bounds access for indexes in this range.
Kind regards, Diego Dias
-- Diego M. Dias, Systems Verification Engineer at Kernkonzept, diego.dias@kernkonzept.com Phone: +49 351 41883231
Kernkonzept GmbH at Dresden, Germany, HRB 31129, CEO Dr.-Ing. Michael Hohmuth
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