Dear Qubes Community, We have published [Qubes Security Bulletin (QSB) 106: Information disclosure through uninitialized memory in libxl](https://github.com/QubesOS/qubes-secpack/blob/4080eab216be36055bcaa6ae855e0023dec5a305/QSBs/qsb-106-2024.txt). The text of this QSB and its accompanying cryptographic signatures are reproduced below, followed by a general explanation of this announcement and authentication instructions.
## Qubes Security Bulletin 106
```
---===[ Qubes Security Bulletin 106 ]===---
2024-11-12
Information disclosure through uninitialized memory in libxl
(XSA-464)
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 2024-11-12, the Xen Project published XSA-464, "libxl leaks data to PVH
guests via ACPI tables" (CVE-2024-45819) [3]:
| PVH guests have their ACPI tables constructed by the toolstack. The
| construction involves building the tables in local memory, which are
| then copied into guest memory. While actually used parts of the local
| memory are filled in correctly, excess space that is being allocated is
| left with its prior contents.
Qubes calls libxl via libvirtd. The memory that is not fully initialized
is allocated via malloc. So the prior content that is leaked to a PVH
qube might be anything that has been previously allocated and then freed
in the libvirtd process.
Impact
-------
The leaked memory usually doesn't contain important secrets [4] but can
reveal various information about other qubes and the host system that is
otherwise not available to a malicious qube. In particular the following
information might be present in libvirtd's memory:
about other qubes:
- Name
- UUID
- kernel version
- kernel cmdline
- IP/MAC addresses of virtual network devices (but not from physical
devices) [5]
- Assigned PCI devices
about the host system:
- Total system memory
- Available PCI devices
- DMI/SYSBIOS information (serial number as reported by firmware, RAM
DIMM product number, etc.)
The list not complete (for example doesn't list less interesting qube
settings like assigned audio qube), but should cover all important
categories.
Note that a malicious qube has very little control about what
information gets leaked in the uninitialized memory that is exposed to
it [6]. Additionally the leak happens only once per start of a qube. So
for a decent change of being leaked interesting information a malicious
qube has to wait a long time for a significant number of normal starts.
Alternatively it can also try to provoke starts of disposable qubes it
can control (for example via qubes.VMShell) or shut itself down and hope
for it being started again by the user or a qrexec call (both methods
easily noticed by a user as unusual activity).
Affected systems
-----------------
All supported version of Qubes are affected.
Only qubes in PVH virt mode are affected (in default setup, every qube
except sys-net and sys-usb).
Patching
---------
The following packages contain security updates that address the
vulnerabilities described in this bulletin:
For Qubes 4.2, in dom0:
- Xen packages, version 4.17.5-4
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-464.html
[4] The leaked memory could reveal the ASLR secret of the libvirtd
process. But this is only useful when the attacker has knowledge of
a memory vulnerability in libvirtd/libxl that is reachable in Qubes
OS. Additionally in a unusual setup a user could have included a
secret in some of the leaked information of other qubes.
[5] Unless the user actively configures something else for a qube, it's
IP addresses is based on it's qid/dispid (number from 0 .. 10000)
and the MAC addresses is the same for all qubes.
[6] When starting a disposable qube via qrexec it could try to time the
start to it's favor.
--
The Qubes Security Team
https://www.qubes-os.org/security/
```
**Source:**
[qsb-106-2024.txt](https://github.com/QubesOS/qubes-secpack/blob/4080eab216be36055bcaa6ae855e0023dec5a305/QSBs/qsb-106-2024.txt)
## [Marek Marczykowski-Górecki](/team/#marek-marczykowski-górecki)'s PGP
signature
```
-----BEGIN PGP SIGNATURE-----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=Fvqs
-----END PGP SIGNATURE-----
```
**Source:**
[qsb-106-2024.txt.sig.marmarek](https://github.com/QubesOS/qubes-secpack/blob/4080eab216be36055bcaa6ae855e0023dec5a305/QSBs/qsb-106-2024.txt.sig.marmarek)
## [Simon Gaiser (aka HW42)](/team/#simon-gaiser-aka-hw42)'s PGP signature
```
-----BEGIN PGP SIGNATURE-----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=c20Y
-----END PGP SIGNATURE-----
```
**Source:**
[qsb-106-2024.txt.sig.simon](https://github.com/QubesOS/qubes-secpack/blob/4080eab216be36055bcaa6ae855e0023dec5a305/QSBs/qsb-106-2024.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](/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)](/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](/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](/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](/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](/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](/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-106), the commands are:
```
$ gpg --verify qsb-106-2024.txt.sig.marmarek qsb-106-2024.txt
$ gpg --verify qsb-106-2024.txt.sig.simon qsb-106-2024.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-106 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/2024/11/12/qsb-106/
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signature.asc
Description: PGP signature
