alpine 3.8
format weakness #12


Weakness Breakdown


A format string exploit occurs when the data of an input string is evaluated as a command by the program. This class of attacks is very similar to buffer overflows since an attacker could execute code, read the stack or cause new behaviors that compromise security. Learn more about format string attacks on OWASP attack index.

Warning code(s):

If format strings can be influenced by an attacker, they can be exploited, and note that sprintf variations do not always 0-terminate.

File Name:



The highlighted line of code below is the trigger point of this particular Alpine 3.8 format weakness.

           ret = avail-1;

      step = MIN (ret, avail-1);
      d->size -= step;
      d->buf += step;

      if (ret != avail-1)
        return ret;

      /* probably glibc 2.0.x truncated output, probe for actual size */
      alloc = MAX (128, ret);
      /* no space to write anything, just probe for size */
      alloc = 128;

      alloc *= 2;
      p = __GMP_ALLOCATE_FUNC_TYPE (alloc, char);
      va_copy (ap, orig_ap);
      ret = vsnprintf (p, alloc, fmt, ap);
      (*__gmp_free_func) (p, alloc);
  while (ret == alloc-1 || ret == -1);

  return ret;

static int
gmp_snprintf_memory (struct gmp_snprintf_t *d, const char *str, size_t len)
  size_t n;

  ASSERT (d->size >= 0);

  if (d->size > 1)
      n = MIN (d->size-1, len);
      memcpy (d->buf, str, n);
      d->buf += n;
      d->size -= n;
  return len;

static int 

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