Information

Advisory

XSA-352

Public release

2020-12-15 12:00

Updated

2020-12-15 12:19

Version

3

CVE(s)

CVE-2020-29486

Title

oxenstored: node ownership can be changed by unprivileged clients

Filesadvisory-352.txt (signed advisory file)
xsa352.meta
xsa352.patchAdvisory

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256

        Xen Security Advisory CVE-2020-29486 / XSA-352
                           version 3

oxenstored: node ownership can be changed by unprivileged clients

UPDATES IN VERSION 3

Public release.

ISSUE DESCRIPTION

Nodes in xenstore have an ownership. In oxenstored, a owner could give a node away. But node ownership has quota implications.

Any guest can run another guest out of quota, or create an unbounded number of nodes owned by dom0, thus running xenstored out of memory

IMPACT

A malicious guest administrator can cause denial of service, against a specific guest or against the whole host.

VULNERABLE SYSTEMS

All systems using oxenstored are vulnerable. Building and using oxenstored is the default in the upstream Xen distribution, if the Ocaml compiler is available.

Systems using C xenstored are not vulnerable.

MITIGATION

There are no mitigations.

Changing to use of C xenstored would avoid this vulnerability. However, given the other vulnerabilities in both versions of xenstored being reported at this time, changing xenstored implementation is not a recommended approach to mitigation of individual issues.

CREDITS

This issue was discovered by Edwin Török of Citrix.

RESOLUTION

Applying the appropriate 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.

xsa352.patch xen-unstable - 4.10

$ sha256sum xsa352* a3b2b2bd4c6b49c472df23f88fb9a5e204d2ba3cd0c3901f8ed057566ef98c85 xsa352.meta 6f9798e20282d4e06f0a8a1abd0d147649e20b33c21559d5a1ea0b1a73a2a4e4 xsa352.patch $

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 -----BEGIN PGP SIGNATURE-----

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Xenproject.org Security Team