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Date: Wed, 10 Aug 2022 13:34:34 -0500
From: John Helmert III <ajak@...too.org>
To: oss-security@...ts.openwall.com
Subject: Re: Apache mod_dav off-by-one
On Tue, Aug 09, 2022 at 02:50:34PM +0300, Evgeny Legerov wrote:
> Hi,
>
>
> How it happens that Apache process_if_header off-by-one, which has been
> mentioned in
>
> The Art of Software Security Assessment (page 420), still remains unpatched?
>
> What am I missing?
Has anyone reported it upstream? Has anyone requested a CVE (seems
unlikely, given the last CVE for mod_dav is one from 2013)?
Upstreams don't magically know about security issues, they need to be
reported to the upstream one way or another.
>
> The code from Apache 2.4.54:
>
> static dav_error * dav_process_if_header(request_rec *r, dav_if_header
> **p_ih)
> {
> ...
>
> while (*list) {
> /* List is the entire production (in a uri scope) */
>
> switch (*list) {
> ...
> case 'N':
> if (list[1] == 'o' && list[2] == 't') {
> if (condition != DAV_IF_COND_NORMAL) {
> return dav_new_error(r->pool, HTTP_BAD_REQUEST,
> DAV_ERR_IF_MULTIPLE_NOT, 0,
> "Invalid \"If:\" header: "
> "Multiple \"not\"
> entries "
> "for the same state.");
> }
> condition = DAV_IF_COND_NOT;
> }
> list += 2;
> break;
>
> It is not only out of bounds read, dav_fetch_next_token() will write
> NULL byte on next iteration.
So we can be more descriptive than calling the vulnerability an
"off-by-one". It's more of an OOB read/write. And if NULL is the only
thing that can be written, it seems likely that the only impact is a
DoS, if that.
>
> regards,
>
> -e
>
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