We have just published Qubes Security Bulletin (QSB) #062: Stack corruption from XSA-346 change (XSA-355). The text of this QSB is reproduced below. This QSB and its accompanying signatures will always be available in the Qubes Security Pack (qubes-secpack).

View QSB #062 in the qubes-secpack:

https://github.com/QubesOS/qubes-secpack/blob/master/QSBs/qsb-062-2020.txt

Learn about the qubes-secpack, including how to obtain, verify, and read it:

https://www.qubes-os.org/security/pack/

View all past QSBs:

https://www.qubes-os.org/security/qsb/

View XSA-355 in the XSA Tracker:

https://www.qubes-os.org/security/xsa/#355



             ---===[ Qubes Security Bulletin #62 ]===---

                             2020-11-24


           Stack corruption from XSA-346 change (XSA-355)


Summary
========

On 2020-11-24, the Xen Security Team published Xen Security Advisory
355 (XSA-355) [1] with the following 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.
| 
| 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.


Patching
=========

The specific packages that resolve the problems discussed in this
bulletin are as follows:

  For Qubes 4.0:
  - Xen packages, version 4.8.5-27
  For Qubes 4.1:
  - Xen packages, version 4.14.0-8

The packages are to be installed in dom0 via the Qube Manager or via
the qubes-dom0-update command as follows:

  For updates from the stable repository (not immediately available):
  $ sudo qubes-dom0-update

  For updates from the security-testing repository:
  $ sudo qubes-dom0-update --enablerepo=qubes-dom0-security-testing

A system restart will be required afterwards.

These packages will migrate from the security-testing repository to the
current (stable) repository over the next two weeks after being tested
by the community.

If you use Anti Evil Maid, you will need to reseal your secret
passphrase to new PCR values, as PCR18+19 will change due to the new
Xen binaries.


Credits
========

See the original Xen Security Advisory.


References
===========

[1] https://xenbits.xen.org/xsa/advisory-355.html

--
The Qubes Security Team
https://www.qubes-os.org/security/