Re: [oss-security] Xen Security Advisory 355 v2 - stack corruption from XSA-346 change

[Mauro Matteo Cascella <mcascell@redhat.com>]

Hello,

Has a CVE been assigned for this issue?

Regards,

On Tue, Nov 24, 2020 at 1:06 PM Xen.org security team <security@xen.org> wrote:
>
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA256
>
>                     Xen Security Advisory XSA-355
>                               version 2
>
>                  stack corruption from XSA-346 change
>
> UPDATES IN VERSION 2
> ====================
>
> Added metadata file.
>
> Public release.
>
> ISSUE DESCRIPTION
> =================
>
> One of the two changes for XSA-346 introduced an on-stack array.  The
> check for guarding against overrunning this array was off by one,
> allowing for corruption of the first stack slot immediately following
> this array.
>
> IMPACT
> ======
>
> A malicious or buggy HVM or PVH guest can cause Xen to crash, resulting
> in a Denial of Service (DoS) to the entire host.  Privilege escalation
> as well as information leaks cannot be excluded.
>
> VULNERABLE SYSTEMS
> ==================
>
> All Xen versions which have the patches for XSA-346 applied are
> vulnerable.
>
> Only x86 HVM and PVH guests can leverage the vulnerability.  Arm guests
> and x86 PV guests cannot leverage the vulnerability.
>
> Only x86 HVM and PVH guests which have physical devices passed through
> to them can leverage the vulnerability.
>
> MITIGATION
> ==========
>
> Not passing through physical devices to untrusted guests will avoid
> the vulnerability.
>
> CREDITS
> =======
>
> This issue was discovered by Jan Beulich of SUSE.
>
> RESOLUTION
> ==========
>
> Applying the attached patch resolves this issue.
>
> Note that patches for released versions are generally prepared to
> apply to the stable branches, and may not apply cleanly to the most
> recent release tarball.  Downstreams are encouraged to update to the
> tip of the stable branch before applying these patches.
>
> xsa355.patch           xen-unstable - Xen 4.10.x
>
> $ sha256sum xsa355*
> a93bfc376897e7cffd095d395f1a66476adb9503d7d80a59b7861e64c2675323  xsa355.meta
> dae633c11cf2eff3e304737265e18ab09213e8e4640458080a944ae7a40819a4  xsa355.patch
> $
>
> NOTE CONCERNING SHORT EMBARGO
> =============================
>
> This issue is likely to be re-discovered as the changes for XSA-346
> are deployed more widely, since the issue is also triggerable without
> any malice or bugginess.
>
> DEPLOYMENT DURING EMBARGO
> =========================
>
> Deployment of the patches and/or mitigations described above (or
> others which are substantially similar) is permitted during the
> embargo, even on public-facing systems with untrusted guest users and
> administrators.
>
> But: Distribution of updated software is prohibited (except to other
> members of the predisclosure list).
>
> Predisclosure list members who wish to deploy significantly different
> patches and/or mitigations, please contact the Xen Project Security
> Team.
>
> (Note: this during-embargo deployment notice is retained in
> post-embargo publicly released Xen Project advisories, even though it
> is then no longer applicable.  This is to enable the community to have
> oversight of the Xen Project Security Team's decisionmaking.)
>
> For more information about permissible uses of embargoed information,
> consult the Xen Project community's agreed Security Policy:
>   http://www.xenproject.org/security-policy.html
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-- 
Mauro Matteo Cascella
Red Hat Product Security
PGP-Key ID: BB3410B0