Created vim tracking bugs for this issue:

Affects: fedora-all [bug 2014662]

marking hosted services affected (low) / delegated solely for presence of affected code.

Flaw summary:

In vim's undo.c, u_save_line() looks like:

u_save_line(undoline_T *ul, linenr_T lnum)
{
    char_u *line = ml_get(lnum);

    if (curbuf->b_ml.ml_line_len == 0)
    {
	ul->ul_len = 1;
	ul->ul_line = vim_strsave((char_u *)"");
    }
    else
    {
	// This uses the length in the memline, thus text properties are
	// included.
	ul->ul_len = curbuf->b_ml.ml_line_len;
	ul->ul_line = vim_memsave(line, ul->ul_len);
    }
    return ul->ul_line == NULL ? FAIL : OK;
}

This flaw involves the line ul->ul_line = vim_memsave(line, ul->ul_len); . Specifically, ul->ul_len can be an incorrect length of `line` if `lnum` is out of range. This causes an out-of-bounds read in vim_memsave() -> mch_memmove() because although the new allocation size is ok, the memory read operation can be an out-of-bounds read of memory pointed to by `p` in:

vim_memsave(char_u *p, size_t len)
{
    char_u *ret = alloc(len);

    if (ret != NULL)
	mch_memmove(ret, p, len);
    return ret;
}

because the `len` parameter (ul->ul_len) doesn't match the proper `len` for `lnum`.

This does not reproduce, nor does it affect versions of vim shipped in any Red Hat Enterprise Linux version because the vulnerable code was introduced in a newer version of vim than those shipped.