We have published Qubes Security Bulletin 092: Buffer overrun in Linux netback driver (XSA-432). 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 092
---===[ Qubes Security Bulletin 092 ]===--- 2023-08-08 Buffer overrun in Linux netback driver (XSA-432) User action required --------------------- Users must install the following specific packages in order to address the issues discussed in this bulletin: For Qubes 4.1, in dom0: - Linux kernel packages (kernel*-qubes-vm), versions 6.1.43, 6.4.8, 5.15.124 For Qubes 4.2, in dom0: - Linux kernel packages (kernel*-qubes-vm), versions 6.1.43, 6.4.8 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.  Once available, the packages are to be installed via the Qubes Update tool or its command-line equivalents.  Service qubes that provide network access (such as sys-net, sys-firewall, sys-whonix, and VPN qubes) must be restarted afterward in order for the updates to take effect. By default, all qubes use a kernel provided by dom0. However, advanced users may opt to modify a given qube so that it uses an in-qube kernel instead.  In such cases, the fixes contained in the kernel packages listed above will not apply. Instead, any fix would have to come from the upstream organization responsible for the distribution running in that qube. If and when the relevant upstream organization makes such a fix available, a normal update  should be sufficient to apply it. The Qubes security team has no control over this process, as it concerns the operations of independent organizations. Those who use in-qube kernels may wish to consider temporarily switching to a dom0-provided kernel. 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 Linux binaries. Summary -------- On 2023-08-08, the Xen Project published XSA-432, "Linux: buffer overrun in netback due to unusual packet" : | The fix for XSA-423 added logic to Linux'es netback driver to deal | with a frontend splitting a packet in a way such that not all of the | headers would come in one piece. Unfortunately the logic introduced | there didn't account for the extreme case of the entire packet being | split into as many pieces as permitted by the protocol, yet still | being smaller than the area that's specially dealt with to keep all | (possible) headers together. Such an unusual packet would therefore | trigger a buffer overrun in the driver. | | An unprivileged guest can cause Denial of Service (DoS) of the host by | sending network packets to the backend, causing the backend to crash. | | Data corruption or privilege escalation seem unlikely but have not | been ruled out. Impact ------- An attacker who manages to compromise a network-connected qube could attempt to exploit the vulnerability described in this bulletin in order to attack the service qube (such as sys-net, sys-firewall, sys-whonix, or a VPN qube) that provides network access to the compromised qube. The Qubes security team believes that such an attack is unlikely to succeed and that this vulnerability is not likely to be exploitable beyond causing a crash. However, if such an attack were successful, it would allow the attacker to execute arbitrary code in the service qube, potentially bypassing the restrictions that such service qubes normally impose. For example: - An attacker in control of sys-firewall could bypass the firewall rules that sys-firewall normally enforces for the qubes connected to it. - An attacker in control of sys-whonix could bypass Tor, emit clearnet traffic, and learn the machine's real public IP address. - An attacker in control of a VPN qube could observe and modify the network traffic of other qubes that are connected to it -- traffic that the VPN would normally protect. - An attacker in control of sys-net could gain direct access to attached PCIe devices. Credits -------- See the original Xen Security Advisory. References -----------  https://www.qubes-os.org/doc/testing/  https://www.qubes-os.org/doc/how-to-update/  https://www.qubes-os.org/doc/managing-vm-kernels/  https://xenbits.xen.org/xsa/advisory-432.html -- The Qubes Security Team https://www.qubes-os.org/security/
Marek Marczykowski-Górecki’s PGP signature
-----BEGIN PGP SIGNATURE----- iQIzBAABCAAdFiEELRdx/k12ftx2sIn61lWk8hgw4GoFAmTSVuQACgkQ1lWk8hgw 4GqonRAAnmq0gEsKrPeUY7gKA4QNPAdqJqplLiXKyuHhJzCyVcL5IJFMKa+ZNEQi QbeXqSkjaZSExGKcDcIwX4+NXIQlG1UYN5vItEJeu9cr8ftIYsM/PUOtnnEspcgD z3H060N9F2MOPUX35LcOsoboNrBj9a5a6lf9+QyiuTb2FfKBTR60K1PPBRDeyLWl W4Ocu5peAiQBtl/f2ce0fF2l3iExHa3QSICS0mkesCD25Uo7bv9LHU0otkWTe4Uy vY58DNvmXWTijKsz10dXvTr0iG3OMTF18LD4DwVp3US1AXEWbhkf1qp+wf0Ysyj+ n/6lbkuexlbrWiTWTecD1ZoStQUxAp9xWIECpWUvWbXcEP7nqhvw+ZwsJgv7hHac LOvNas3Dlk+VrqhxxMrRi2tSO+FSoi/wxQJXdwWFvsUiX/C5MtkKoDebcvoqTKWy RDE/tsw/YZON7GPoZRtGCcWuhNCHRaekeRCuod2U0inCxqvam/nnAs2+dz0c2HuZ 34yuhbs6z7zt+pYefN82AGqlGF7cUQKo3JDH7FWQc9lwmd7/aGhpYO890HNIpsPm nKLGa0Q2oTAxSLvhKXUsufp3L5Ijf/eyOLnYH6CulPeyew1Nxs9Igr6/IM8IL3Gb iztOSbJtUhWWDB2U3opqBUk8tO0391bVG3POYtDxdz+NH4PPy8Y= =Tgo/ -----END PGP SIGNATURE-----
Simon Gaiser (aka HW42)’s PGP signature
-----BEGIN PGP SIGNATURE----- iQIzBAABCgAdFiEE6hjn8EDEHdrv6aoPSsGN4REuFJAFAmTSS2kACgkQSsGN4REu FJDQdg/+MZ2uhYeY9Qtbw4oSDhEjnCkr9H/GiTuOg93fZqXMS+pQXtJ0GL9Skok2 qh/RK7jc1pKuKrcsRU2Fnd0dcmtX8Si5Je0R5zYVxmnWwMUhtfnNMmD6u9Kau4HV yWLKy2PsY3zLuzBNLgfmKw2HindKitx57tvxcGGlC1RE+yaQNDIPd1A6NwsLrsSO uNoFco+vSrTt9iJPgoeJw3RzWmobCS0zzvBgp5IY/ZJgiypxw12o2ZA8LPDEob+y atPTD6OU/fCANOIzGD0+fVrRuI/22BW2Hgq4DzJhBXzCuHBwvY0h+UcXtAjJ90bi sssUs2/vcG440SaBIJSCrGOCwjUg++MXZW6ayAjN/Ph3K+gE9sb84sHDP/UDNecX q5fxrgsj2+cIjxwG7ZT/kz2z7FwcotWYw60agwCejJgTptGL9CzgxGcZ5s+76ZpD nVUgblsjm2w1dIjYPWF5I+iZ/SOVNas3pvPBnjqQstD+chD6Ph+ESlKzEBszv8ae 5OgmNBP9JBr2TQyxQBGEieipX6i91V6nKK/7kgvCZoU3Neipd6wydraVowLj5uRY 7O/knYJNE8U9p65l2FRHTcsCS51q4tE9EUc6Vhm7iTK9q6969gIyiZy+wapc0Bs1 /cw1j2Gq+NU4oZb6Upsbie3srFpR9+faN5mUAp79zASI7TyEutA= =NDn+ -----END PGP SIGNATURE-----
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. A QSB typically provides a summary and impact analysis of one or more recently-discovered software vulnerabilities, including details about patching to address them. A list of all QSBs is available here.
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. 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 signature is a cryptographic digital signature made in accordance with the OpenPGP standard. PGP signatures can be cryptographically verified with programs like GNU Privacy Guard (GPG). 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
gpg installed. (See here for Windows and Mac options.)
Obtain the Qubes Master Signing Key (QMSK), e.g.:
$ 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
(See here for more ways to obtain the QMSK.)
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.)
$ 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
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. See here for more details and ideas for how to do that.
Tip: Record the genuine QMSK fingerprint in a safe place (or several) so that you don’t have to repeat this step in the future.
Once you are satisfied that you have the genuine QMSK, set its trust level to 5 (“ultimate”), then quit GnuPG with
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
Use Git to clone the qubes-secpack repo.
$ 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.
Import the included PGP keys. (See our PGP key policies for important information about these keys.)
$ 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
Verify signed Git tags.
$ 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.
Verify PGP signatures, e.g.:
$ 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 --verifycommand should always start with
gpg: Good signature from...followed by an appropriate key.
For this announcement (QSB-092), the commands are:
$ gpg --verify qsb-092-2023.txt.sig.marmarek qsb-092-2023.txt $ gpg --verify qsb-092-2023.txt.sig.simon qsb-092-2023.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-092 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 is a companion discussion topic for the original entry at https://www.qubes-os.org/news/2023/08/08/qsb-092/