This document has come in effect in December 2011 and will be reviewed periodically (see revision sections). The last modification has been made in (approval date tbd).


Computer systems have bugs. Currently recognised best practice for bugs with security implications is to notify significant downstream users in private; leave a reasonable interval for downstreams to respond and prepare updated software packages; then make public disclosure.

We want to encourage people to report bugs they find to us. Therefore we will treat with respect the requests of discoverers, or other vendors, who report problems to us.

Scope of this process

This process primarily covers the Xen Hypervisor Project. Vulnerabilties reported against other Xen Project teams will be handled on a best effort basis by the relevant Project Lead together with the Security Response Team.

Specific process

  1. We request that anyone who discovers a vulnerability in Xen Project software reports this by email to security (at) xenproject (dot) org. (This also covers the situation where an existing published changeset is retrospectively found to be a security fix)

  2. Immediately, and in parallel:

    1. Those of us on the Hypervisor team who are aware of the problem will notify security@xenproject if disclosure wasn't made there already.

    2. If the vulnerability is not already public, security@xenproject will negotiate with discoverer regarding embargo date and disclosure schedule. See below for detailed discussion.

  3. Furthermore, also in parallel:
      1. security@xenproject will check whether the discoverer, or other people already aware of the problem, have allocated a CVE number. If not, we will acquire a CVE candidate number ourselves, and make sure that everyone who is aware of the problem is also aware of the CVE number.

      2. If we think other software systems (for example, competing hypervisor systems) are likely to be affected by the same vulnerability, we will try to make those other projects aware of the problem and include them in the advisory preparation process.

    (This may rely on the other project(s) having documented and responsive security contact points)

    1. We will prepare or check patch(es) which fix the vulnerability. This would ideally include all relevant backports. Patches will be tightly targeted on fixing the specific security vulnerability in the smallest, simplest and most reliable way. Where necessary domain specific experts within the community will be brought in to help with patch preparation.

    2. We will determine which systems/configurations/versions are vulnerable, and what the impact of the vulnerability is. Depending on the nature of the vulnerability this may involve sharing information about the vulnerability (in confidence, if the issue is embargoed) with hardware vendors and/or other software projects.

    3. We will write a Xen advisory including information from (b)-(f)

  4. Advisory pre-release:

    This occurs only if the advisory is embargoed (ie, the problem is not already public):

    As soon as our advisory is available, we will send it, including patches, to members of the Xen security pre-disclosure list. For more information about this list, see below.

    At this stage the advisory will be clearly marked with the embargo date.

  5. Advisory public release:

    At the embargo date we will publish the advisory, and push bugfix changesets to public revision control trees.

    Public advisories will be posted to xen-devel, xen-users and xen-annnounce and will be added to the Security Announcements wiki page. Copies will also be sent to the pre-disclosure list.

  6. Updates

    If new information or better patches become available, or we discover mistakes, we may issue an amended (revision 2 or later) public advisory. This will also be sent to the pre-disclosure list.

  7. Post embargo transparency:

    During an embargo period the Security Response Team may be required to make potentially controverial decisions in private, since they cannot confer with the community without breaking the embargo. The Security Response Team will attempt to make such decisions following the guidance of this document and where necessary their own best judgement. Following the embargo period any such decisions will be disclosed to the community in the interests of transparency and to help provide guidance should a similar decision be required in the future.

Embargo and disclosure schedule

If a vulnerability is not already public, we would like to notify significant distributors and operators of Xen so that they can prepare patched software in advance. This will help minimise the degree to which there are Xen users who are vulnerable but can't get patches.

As discussed, we will negotiate with discoverers about disclosure schedule. Our usual starting point for that negotiation, unless there are reasons to diverge from this, would be:

  1. One working week between notification arriving at security@xenproject and the issue of our own advisory to our predisclosure list. We will use this time to gather information and prepare our advisory, including required patches.

  2. Two working weeks between issue of our advisory to our predisclosure list and publication.

When a discoverer reports a problem to us and requests longer delays than we would consider ideal, we will honour such a request if reasonable. If a discoverer wants an accelerated disclosure compared to what we would prefer, we naturally do not have the power to insist that a discoverer waits for us to be ready and will honour the date specified by the discoverer.

Naturally, if a vulnerability is being exploited in the wild we will make immediately public release of the advisory and patch(es) and expect others to do likewise.

Pre-disclosure list

The Xen Project operates a pre-disclosure list. This list contains the email addresses (ideally, role addresses) of the security response teams for significant Xen operators and distributors.

This includes:

This includes both corporations and community institutions.

Here "provider", "vendor", and "distributor" is meant to include anyone who is making a genuine service, available to the public, whether for a fee or gratis. For projects providing a service for a fee, the rule of thumb of "genuine" is that you are offering services which people are purchasing. For gratis projects, the rule of thumb for "genuine" is measured in terms of the amount of time committed to providing the service. For instance, a software project which has 2-3 active developers, each of whom spend 3-4 hours per week doing development, is very likely to be accepted; whereas a project with a single developer who spends a few hours a month will most likey be rejected.

For organizational users, a rule of thumb is that "large scale" means an installed base of 300,000 or more Xen guests.

The list of entities on the pre-disclosure list is public. (Just the list of projects and organisations, not the actual email addresses.)

If there is an embargo, the pre-disclosure list will receive copies of the advisory and patches, with a clearly marked embargo date, as soon as they are available. The pre-disclosure list will also receive copies of public advisories when they are first issued or updated

Handling of embargoed information

Organizations on the pre-disclosure list are expected to maintain the confidentiality of the vulnerability up to the embargo date which security@xenproject have agreed with the discoverer, and are committing to ensuring that any members/employees of that organisation who come into contact with confidential information will do so as well..

Specifically, prior to the embargo date, pre-disclosure list members should not make available, even to their own customers and partners:

without prior consultation with security@xenproject.

List members are allowed to make available to their users only the following:

List members may, if (and only if) the Security Team grants permission, deploy fixed versions during the embargo. Permission for deployment, and any restrictions, will be stated in the embargoed advisory text.

The Security Team will normally permit such deployment, even for systems where VMs are managed or used by non-members of the predisclosure list. The Security Team will impose deployment restrictions only insofar as it is necessary to prevent the exposure of technicalities (for example, differences in behaviour) which present a significant risk of rediscovery of the vulnerability. Such situations are expected to be rare.

Where the list member is a service provider who intends to take disruptive action such as rebooting as part of deploying a fix: the list member's communications to its users about the service disruption may mention that the disruption is to correct a security issue, and relate it to the public information about the issue (as listed above). This applies whether the deployment occurs during the embargo (with permission - see above) or is planned for after the end of the embargo.

NOTE: Prior v2.2 of this policy (25 June 2014) it was permitted to also make available the allocated CVE number. This is no longer permitted in accordance with MITRE policy.

Information-sharing amongst predisclosure list members

Predisclosure list members are allowed to share fixes to embargoed issues, analysis, etc., with the security teams of other list members. Technical measures must be taken to prevents non-list-member organisations, or unauthorised staff in list-member organisations, from obtaining the embargoed materials.

The Xen Project provides the mailing list xen-security-issues-discuss@lists.xenproject<dot>org for this purpose. List members are encouraged to use it but may share with other list members' security teams via other channels.

The -discuss list's distribution is identical to that of the primary predisclosure list xen-security-issues. Recipient organisations who do not wish to receive all of the traffic on -discuss should use recipient-side email filtering based on the provided List-Id.

The -discuss list is moderated by the Xen Project Security Team. Announcements of private availability of fixed versions, and technical messages about embargoed advisories, will be approved. Messages dealing with policy matters will be rejected with a reference to the Security Team contact address and/or public Xen mailing lists.

Predisclosure list membership application process

Organisations who meet the criteria should contact predisclosure-applications@xenproject<dot>org (which is a public mailing list) if they wish to receive pre-disclosure of advisories.

You must include in the e-mail:

Your application will be determined by the Xen Project Security Team, and their decision posted to the list. The Security Team has no discretion to accept applications which do not provide all of the information required above.

If you are dissatisfied with the Security Team's decision you may appeal it via the Xen Project's governance processes.

Organisations should not request subscription via the mailing list web interface. Any such subscription requests will be rejected and ignored.

A role address (such as should be used for each organisation, rather than one or more individual's direct email address. This helps to ensure that changes of personnel do not end up effectively dropping an organisation from the list.

Organizations on the pre-disclosure list:

This is a list of organisations on the pre-disclosure list (not email addresses or internal business groups).

Change History