We have just published Qubes Security Bulletin (QSB) 083: Retbleed: Arbitrary speculative code execution with return instructions (XSA-407). 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-083 in the qubes-secpack:


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             ---===[ Qubes Security Bulletin 083 ]===---



                Arbitrary speculative code execution
                 with return instructions (XSA-407)

User action required

Users must install the following specific packages in order to address
the issues discussed in this bulletin:

  For Qubes 4.0, in dom0:
  - Xen packages, version 4.8.5-43

  For Qubes 4.1, in dom0:
  - Xen packages, version 4.14.5-6

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. [1] Once available, the packages are to be installed
via the Qubes Update tool or its command-line equivalents. [2]

Dom0 must be restarted afterward in order for the updates to take

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.


On 2022-07-12, the Xen Project published XSA-407, "Retbleed -
arbitrary speculative code execution with return instructions" [3]:

| Researchers at ETH Zurich have discovered Retbleed, allowing for
| arbitrary speculative execution in a victim context.
| For more details, see:
|   https://comsec.ethz.ch/retbleed
| ETH Zurich have allocated CVE-2022-29900 for AMD and CVE-2022-29901 for
| Intel.
| Despite the similar preconditions, these are very different
| microarchitectural behaviours between vendors.
| On AMD CPUs, Retbleed is one specific instance of a more general
| microarchitectural behaviour called Branch Type Confusion.  AMD have
| assigned CVE-2022-23816 (Retbleed) and CVE-2022-23825 (Branch Type
| Confusion).
| For more details, see:
|   https://www.amd.com/en/corporate/product-security/bulletin/amd-sb-1037
| On Intel CPUs, Retbleed is not a new vulnerability; it is only
| applicable to software which did not follow Intel's original
| Spectre-v2 guidance.  Intel are using the ETH Zurich allocated
| CVE-2022-29901.
| For more details, see:
|   https://www.intel.com/content/www/us/en/security-center/advisory/intel-sa-00702.html
|   https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/advisory-guidance/return-stack-buffer-underflow.html
| ARM have indicated existing guidance on Spectre-v2 is sufficient.


This is yet another speculative execution issue, which allows an
attacker to infer content of memory they shouldn't have access to. This
includes one VM extracting secrets from another. Any VM can perform this
attack on an affected hardware.

AMD systems based on Zen 1 - Zen 2 microarchitectures are affected.
Specifically those are AMD Ryzen processors with model names 1xxx - 4xxx
and some 5xxxU [4]. Zen 3 microarchitecture (AMD Ryzen 5xxx or newer)
are not affected.

Pre-existing Xen mitigations on Intel machines are effective to prevent
this issue, so Intel systems are not affected.


See the original Xen Security Advisory.


[1] https://www.qubes-os.org/doc/testing/
[2] https://www.qubes-os.org/doc/how-to-update/
[3] https://xenbits.xen.org/xsa/advisory-407.html
[4] Unlike other 5xxxU models, Ryzen 3 5300U, Ryzen 5 5500U and
    Ryzen 7 5700U are Zen 2, not Zen 3. See

The Qubes Security Team