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Tue, 10 Nov 2026 08:48:16 +0000 (UTC) Received: from redhat.com (headnet04.pony-001.prod.iad2.dc.redhat.com [10.2.32.116]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 998771961755; Tue, 10 Nov 2026 08:48:14 +0000 (UTC) Date: Tue, 10 Nov 2026 08:48:11 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Eric Blake Cc: Stefan Hajnoczi , qemu-devel@nongnu.org, qemu-stable@nongnu.org, qemu-block@nongnu.org, Pierrick Bouvier Subject: Re: [PATCH v2 1/3] docs: Mention security considerations for NBD Message-ID: References: <20261107225834.778738-5-eblake@redhat.com> <20261107225834.778738-6-eblake@redhat.com> <20261109155847.GD429574@shajnocz.csb> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/2.4.3 (2026-10-09) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, MARKETING_PARTNERS=0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org X-Spam-Status: No, score=-7.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MARKETING_PARTNERS,SPF_HELO_PASS,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Mon, Nov 09, 2026 at 02:48:18PM -0600, Eric Blake wrote: > On Mon, Nov 09, 2026 at 08:58:47AM -0700, Stefan Hajnoczi wrote: > > On Sat, Nov 07, 2026 at 04:54:36PM -0600, Eric Blake wrote: > > > +Proper hardening of network connections can prevent the use of > > > +untrusted clients, and is therefore a factor when considering whether > > > +a malicious network partner that intentionally violates the > > > +communication protocol to trigger a QEMU bug can be treated as a lower > > > +priority bug. > > > > IMO there is no such thing as a trusted client - QEMU needs to validate > > all inputs. When a client is authorized to use a resource (e.g. an NBD > > export) it can still be rogue and trigger a Denial of Service that > > affects the guest or other clients. > > > > > Did you add this because there was no CVE assigned yet? Maybe you can > > remove this since a CVE has been assigned? > > I've got at least one other bug pending that I'm about to lift > confidentiality on, in the same boat where TLS prevents untrusted > client behavior, but where I don't have a CVE number yet. But I agree > that since we don't fully control even a trusted client process, ANY > flaw in the client that allows the client to start sending > non-compliant data over the wire can then be escalated further into an > attack on QEMU, despite QEMU minimizing the risk of such attacks by > first filtering out obvious untrusted clients. > > I'm trying to figure out the best balance of wording for that. In the > CVSS scoring system [1], you are arguing (and I agree) that the CVSS-B > base score is unchanged by whether or not TLS was in use (we don't > control the remote client; if the remote client can send non-compliant > bytes over the wire, QEMU will assert). However, the environmental > metrics of CVSS-BE cover Attack Complexity (AC) and Attack > Requirements (AR) that consider how hard it is to get the client to be > non-compliant in the first place. Once attack chaining is involved, > the risk to QEMU is less than if the attacker does not first have to > compromise a trusted client into sending non-compliant bytes. > > [1] https://nvd.nist.gov/vuln-metrics/cvss/v3-calculator > > Maybe the solution is as simple as rewording "trusted client" into > "authenticated client", to emphasize that while any client misbehavior > that can crash QEMU is still likely to be a CVE, the authentication > aspect affects the Environmental analysis which in turn reduces the > overall CVSS-BE rating of the attack. Yes, using 'authenticated client' is a better term, as that is more of a clear "fact", where as "trusted client" can mean many different things in different people & scenarios With regards, Daniel -- |: https://berrange.com ~~ https://hachyderm.io/@berrange :| |: https://libvirt.org ~~ https://entangle-photo.org :| |: https://pixelfed.art/berrange ~~ https://fstop138.berrange.com :|