Dear Qubes Community,
We have published [Qubes Security Bulletin 096: BTC/SRSO fixes not fully
effective
(XSA-446)](https://github.com/QubesOS/qubes-secpack/blob/main/QSBs/qsb-096-2023.txt).
The text of this QSB and its accompanying cryptographic signatures are
reproduced below. For an explanation of this announcement and instructions for
authenticating this QSB, please see the end of this announcement.
## Qubes Security Bulletin 096
```
---===[ Qubes Security Bulletin 096 ]===---
2023-11-14
BTC/SRSO fixes not fully effective (XSA-446)
User action
------------
Continue to update normally [1] in order to receive the security updates
described in the "Patching" section below. No other user action is
required in response to this QSB.
Summary
--------
On 2023-11-14, the Xen Project published XSA-446, "x86: BTC/SRSO fixes
not fully effective" [3]:
| The fixes for XSA-422 (Branch Type Confusion) and XSA-434 (Speculative
| Return Stack Overflow) are not IRQ-safe. It was believed that the
| mitigations always operated in contexts with IRQs disabled.
|
| However, the original XSA-254 fix for Meltdown (XPTI) deliberately
| left interrupts enabled on two entry paths; one unconditionally, and
| one conditionally on whether XPTI was active.
|
| As BTC/SRSO and Meltdown affect different CPU vendors, the mitigations
| are not active together by default. Therefore, there is race
| condition whereby a malicious PV guest can bypass BTC/SRSO protections
| and launch a BTC/SRSO attack against Xen.
Impact
-------
The impact is the same as it was in QSB-086 [4]:
| On Qubes OS installations with affected CPUs, a VM running in PV mode
| may be capable of inferring the memory contents of other running VMs,
| including dom0. In the default Qubes OS configuration, only the
| stubdomains for HVMs are in a position to exploit this vulnerability
| in order to attack other VMs. (Dom0 also runs in PV mode, but it is
| fully trusted.)
Affected systems
-----------------
Only x86 AMD and Hygon systems are vulnerable.
Patching
---------
The following packages contain security updates that address the
vulnerabilities described in this bulletin:
For Qubes 4.1, in dom0:
- Xen packages, version 4.14.6-4
For Qubes 4.2, in dom0:
- Xen packages, version 4.17.2-5
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. [2] Once available, the packages are to be installed
via the Qubes Update tool or its command-line equivalents. [1]
Dom0 must be restarted afterward in order for the updates to take
effect.
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://www.qubes-os.org/doc/how-to-update/
[2] https://www.qubes-os.org/doc/testing/
[3] https://xenbits.xen.org/xsa/advisory-446.html
[4] https://www.qubes-os.org/news/2022/11/08/qsb-086/
--
The Qubes Security Team
https://www.qubes-os.org/security/
```
*Source*:
<https://github.com/QubesOS/qubes-secpack/blob/main/QSBs/qsb-096-2023.txt>
## [Marek
Marczykowski-Górecki](https://www.qubes-os.org/team/#marek-marczykowski-górecki)'s
PGP signature
```
-----BEGIN PGP SIGNATURE-----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=nzwT
-----END PGP SIGNATURE-----
```
*Source*:
<https://github.com/QubesOS/qubes-secpack/blob/main/QSBs/qsb-096-2023.txt.sig.marmarek>
## [Simon Gaiser (aka
HW42)](https://www.qubes-os.org/team/#simon-gaiser-aka-hw42)'s PGP signature
```
-----BEGIN PGP SIGNATURE-----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=ANw6
-----END PGP SIGNATURE-----
```
*Source*:
<https://github.com/QubesOS/qubes-secpack/blob/main/QSBs/qsb-096-2023.txt.sig.simon>
## What is the purpose of this announcement?
The purpose of this announcement is to inform the Qubes community that a new
Qubes security bulletin (QSB) has been published.
## What is a Qubes security bulletin (QSB)?
A Qubes security bulletin (QSB) is a security announcement issued by the [Qubes
security team](https://www.qubes-os.org/security/#qubes-security-team). A QSB
typically provides a summary and impact analysis of one or more
recently-discovered software vulnerabilities, including details about patching
to address them. For a list of all QSBs, see [Qubes security bulletins
(QSBs)](https://www.qubes-os.org/security/qsb/).
## Why should I care about QSBs?
QSBs tell you what actions you must take in order to protect yourself from
recently-discovered security vulnerabilities. In most cases, security
vulnerabilities are addressed by [updating
normally](https://www.qubes-os.org/doc/how-to-update/). However, in some cases,
special user action is required. In all cases, the required actions are
detailed in QSBs.
## What are the PGP signatures that accompany QSBs?
A [PGP](https://en.wikipedia.org/wiki/Pretty_Good_Privacy) signature is a
cryptographic [digital
signature](https://en.wikipedia.org/wiki/Digital_signature) made in accordance
with the [OpenPGP](https://en.wikipedia.org/wiki/Pretty_Good_Privacy#OpenPGP)
standard. PGP signatures can be cryptographically verified with programs like
[GNU Privacy Guard (GPG)](https://gnupg.org/). The Qubes security team
cryptographically signs all QSBs so that Qubes users have a reliable way to
check whether QSBs are genuine. The only way to be certain that a QSB is
authentic is by verifying its PGP signatures.
## Why should I care whether a QSB is authentic?
A forged QSB could deceive you into taking actions that adversely affect the
security of your Qubes OS system, such as installing malware or making
configuration changes that render your system vulnerable to attack. Falsified
QSBs could sow fear, uncertainty, and doubt about the security of Qubes OS or
the status of the Qubes OS Project.
## How do I verify the PGP signatures on a QSB?
The following command-line instructions assume a Linux system with `git` and
`gpg` installed. (For Windows and Mac options, see [OpenPGP
software](https://www.qubes-os.org/security/verifying-signatures/#openpgp-software).)
1. Obtain the Qubes Master Signing Key (QMSK), e.g.:
```shell_session
$ gpg --fetch-keys
https://keys.qubes-os.org/keys/qubes-master-signing-key.asc
gpg: directory '/home/user/.gnupg' created
gpg: keybox '/home/user/.gnupg/pubring.kbx' created
gpg: requesting key from
'https://keys.qubes-os.org/keys/qubes-master-signing-key.asc'
gpg: /home/user/.gnupg/trustdb.gpg: trustdb created
gpg: key DDFA1A3E36879494: public key "Qubes Master Signing Key" imported
gpg: Total number processed: 1
gpg: imported: 1
```
(For more ways to obtain the QMSK, see [How to import and authenticate the
Qubes Master Signing
Key](https://www.qubes-os.org/security/verifying-signatures/#how-to-import-and-authenticate-the-qubes-master-signing-key).)
2. View the fingerprint of the PGP key you just imported. (Note: `gpg>`
indicates a prompt inside of the GnuPG program. Type what appears after it when
prompted.)
```shell_session
$ gpg --edit-key 0x427F11FD0FAA4B080123F01CDDFA1A3E36879494
gpg (GnuPG) 2.2.27; Copyright (C) 2021 Free Software Foundation, Inc.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
pub rsa4096/DDFA1A3E36879494
created: 2010-04-01 expires: never usage: SC
trust: unknown validity: unknown
[ unknown] (1). Qubes Master Signing Key
gpg> fpr
pub rsa4096/DDFA1A3E36879494 2010-04-01 Qubes Master Signing Key
Primary key fingerprint: 427F 11FD 0FAA 4B08 0123 F01C DDFA 1A3E 3687 9494
```
3. *Important*: At this point, you still don't know whether the key you just
imported is the genuine QMSK or a forgery. In order for this entire procedure
to provide meaningful security benefits, you *must* authenticate the QMSK
out-of-band. *Do not skip this step*! The standard method is to obtain the QMSK
fingerprint from *multiple independent sources in several different ways* and
check to see whether they match the key you just imported. For more
information, see [How to import and authenticate the Qubes Master Signing
Key](https://www.qubes-os.org/security/verifying-signatures/#how-to-import-and-authenticate-the-qubes-master-signing-key).
*Tip*: After you have authenticated the QMSK out-of-band to your
satisfaction, record the QMSK fingerprint in a safe place (or several) so that
you don't have to repeat this step in the future.
4. Once you are satisfied that you have the genuine QMSK, set its trust level
to 5 ("ultimate"), then quit GnuPG with `q`.
```shell_session
gpg> trust
pub rsa4096/DDFA1A3E36879494
created: 2010-04-01 expires: never usage: SC
trust: unknown validity: unknown
[ unknown] (1). Qubes Master Signing Key
Please decide how far you trust this user to correctly verify other users'
keys
(by looking at passports, checking fingerprints from different sources, etc.)
1 = I don't know or won't say
2 = I do NOT trust
3 = I trust marginally
4 = I trust fully
5 = I trust ultimately
m = back to the main menu
Your decision? 5
Do you really want to set this key to ultimate trust? (y/N) y
pub rsa4096/DDFA1A3E36879494
created: 2010-04-01 expires: never usage: SC
trust: ultimate validity: unknown
[ unknown] (1). Qubes Master Signing Key
Please note that the shown key validity is not necessarily correct
unless you restart the program.
gpg> q
```
5. Use Git to clone the qubes-secpack repo.
```shell_session
$ git clone https://github.com/QubesOS/qubes-secpack.git
Cloning into 'qubes-secpack'...
remote: Enumerating objects: 4065, done.
remote: Counting objects: 100% (1474/1474), done.
remote: Compressing objects: 100% (742/742), done.
remote: Total 4065 (delta 743), reused 1413 (delta 731), pack-reused 2591
Receiving objects: 100% (4065/4065), 1.64 MiB | 2.53 MiB/s, done.
Resolving deltas: 100% (1910/1910), done.
```
6. Import the included PGP keys. (See our [PGP key
policies](https://www.qubes-os.org/security/pack/#pgp-key-policies) for
important information about these keys.)
```shell_session
$ gpg --import qubes-secpack/keys/*/*
gpg: key 063938BA42CFA724: public key "Marek Marczykowski-Górecki (Qubes OS
signing key)" imported
gpg: qubes-secpack/keys/core-devs/retired: read error: Is a directory
gpg: no valid OpenPGP data found.
gpg: key 8C05216CE09C093C: 1 signature not checked due to a missing key
gpg: key 8C05216CE09C093C: public key "HW42 (Qubes Signing Key)" imported
gpg: key DA0434BC706E1FCF: public key "Simon Gaiser (Qubes OS signing key)"
imported
gpg: key 8CE137352A019A17: 2 signatures not checked due to missing keys
gpg: key 8CE137352A019A17: public key "Andrew David Wong (Qubes
Documentation Signing Key)" imported
gpg: key AAA743B42FBC07A9: public key "Brennan Novak (Qubes Website &
Documentation Signing)" imported
gpg: key B6A0BB95CA74A5C3: public key "Joanna Rutkowska (Qubes Documentation
Signing Key)" imported
gpg: key F32894BE9684938A: public key "Marek Marczykowski-Górecki (Qubes
Documentation Signing Key)" imported
gpg: key 6E7A27B909DAFB92: public key "Hakisho Nukama (Qubes Documentation
Signing Key)" imported
gpg: key 485C7504F27D0A72: 1 signature not checked due to a missing key
gpg: key 485C7504F27D0A72: public key "Sven Semmler (Qubes Documentation
Signing Key)" imported
gpg: key BB52274595B71262: public key "unman (Qubes Documentation Signing
Key)" imported
gpg: key DC2F3678D272F2A8: 1 signature not checked due to a missing key
gpg: key DC2F3678D272F2A8: public key "Wojtek Porczyk (Qubes OS
documentation signing key)" imported
gpg: key FD64F4F9E9720C4D: 1 signature not checked due to a missing key
gpg: key FD64F4F9E9720C4D: public key "Zrubi (Qubes Documentation Signing
Key)" imported
gpg: key DDFA1A3E36879494: "Qubes Master Signing Key" not changed
gpg: key 1848792F9E2795E9: public key "Qubes OS Release 4 Signing Key"
imported
gpg: qubes-secpack/keys/release-keys/retired: read error: Is a directory
gpg: no valid OpenPGP data found.
gpg: key D655A4F21830E06A: public key "Marek Marczykowski-Górecki (Qubes
security pack)" imported
gpg: key ACC2602F3F48CB21: public key "Qubes OS Security Team" imported
gpg: qubes-secpack/keys/security-team/retired: read error: Is a directory
gpg: no valid OpenPGP data found.
gpg: key 4AC18DE1112E1490: public key "Simon Gaiser (Qubes Security Pack
signing key)" imported
gpg: Total number processed: 17
gpg: imported: 16
gpg: unchanged: 1
gpg: marginals needed: 3 completes needed: 1 trust model: pgp
gpg: depth: 0 valid: 1 signed: 6 trust: 0-, 0q, 0n, 0m, 0f, 1u
gpg: depth: 1 valid: 6 signed: 0 trust: 6-, 0q, 0n, 0m, 0f, 0u
```
7. Verify signed Git tags.
```shell_session
$ cd qubes-secpack/
$ git tag -v `git describe`
object 266e14a6fae57c9a91362c9ac784d3a891f4d351
type commit
tag marmarek_sec_266e14a6
tagger Marek Marczykowski-Górecki 1677757924 +0100
Tag for commit 266e14a6fae57c9a91362c9ac784d3a891f4d351
gpg: Signature made Thu 02 Mar 2023 03:52:04 AM PST
gpg: using RSA key 2D1771FE4D767EDC76B089FAD655A4F21830E06A
gpg: Good signature from "Marek Marczykowski-Górecki (Qubes security pack)"
[full]
```
The exact output will differ, but the final line should always start with
`gpg: Good signature from...` followed by an appropriate key. The `[full]`
indicates full trust, which this key inherits in virtue of being validly signed
by the QMSK.
8. Verify PGP signatures, e.g.:
```shell_session
$ cd QSBs/
$ gpg --verify qsb-087-2022.txt.sig.marmarek qsb-087-2022.txt
gpg: Signature made Wed 23 Nov 2022 04:05:51 AM PST
gpg: using RSA key 2D1771FE4D767EDC76B089FAD655A4F21830E06A
gpg: Good signature from "Marek Marczykowski-Górecki (Qubes security pack)"
[full]
$ gpg --verify qsb-087-2022.txt.sig.simon qsb-087-2022.txt
gpg: Signature made Wed 23 Nov 2022 03:50:42 AM PST
gpg: using RSA key EA18E7F040C41DDAEFE9AA0F4AC18DE1112E1490
gpg: Good signature from "Simon Gaiser (Qubes Security Pack signing key)"
[full]
$ cd ../canaries/
$ gpg --verify canary-034-2023.txt.sig.marmarek canary-034-2023.txt
gpg: Signature made Thu 02 Mar 2023 03:51:48 AM PST
gpg: using RSA key 2D1771FE4D767EDC76B089FAD655A4F21830E06A
gpg: Good signature from "Marek Marczykowski-Górecki (Qubes security pack)"
[full]
$ gpg --verify canary-034-2023.txt.sig.simon canary-034-2023.txt
gpg: Signature made Thu 02 Mar 2023 01:47:52 AM PST
gpg: using RSA key EA18E7F040C41DDAEFE9AA0F4AC18DE1112E1490
gpg: Good signature from "Simon Gaiser (Qubes Security Pack signing key)"
[full]
```
Again, the exact output will differ, but the final line of output from each
`gpg --verify` command should always start with `gpg: Good signature from...`
followed by an appropriate key.
For this announcement (QSB-096), the commands are:
```
$ gpg --verify qsb-096-2023.txt.sig.marmarek qsb-096-2023.txt
$ gpg --verify qsb-096-2023.txt.sig.simon qsb-096-2023.txt
```
You can also verify the signatures directly from this announcement in addition
to or instead of verifying the files from the qubes-secpack. Simply copy and
paste the QSB-096 text into a plain text file and do the same for both
signature files. Then, perform the same authentication steps as listed above,
substituting the filenames above with the names of the files you just created.
This announcement is also available on the Qubes website:
https://www.qubes-os.org/news/2023/11/14/qsb-096/
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