QSB-122: Package verification bypass in APT (DSA-6607-1)

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 122 ---===[ Qubes Security Bulletin 122 ]===--- 2026-11-06 User action ------------ If you update Qubes OS using the Qubes Update tool, continue to update normally in order to receive the security updates described in the "Patching" section below. If you update Qubes OS using command-line tools instead of the Qubes Update tool, you must first update dom0 by itself (without any other qubes) via `qubes-dom0-update` in a dom0 terminal.

Only after dom0 has been successfully updated should you update all Debian and Whonix templates and standalones via `qubes-vm-update` in a dom0 terminal. (The Qubes Update tool automatically handles updating in the correct order.) Do not attempt to update any qube using the `apt` command directly, as this bypasses built-in Qubes OS update security measures. Use only the Qubes Update tool or its command-line equivalents in the order described above. [1] After updating dom0 and all Debian and Whonix templates and standalones, we recommend restarting all Debian and Whonix qubes to ensure the updates take effect. Summary -------- On 2026-11-04, the Debian security team published DSA 6607-1, "apt security update" (CVE-2026-109518) [3]: | Max Justicz discovered a vulnerability in the APT package manager.

APT | can merge two different package downloads after an HTTP redirect gives | them the same URI. Improper file handling when resuming an HTTP | download allows a man-in-the-middle attacker to replace a package | after verification, resulting in the execution of arbitrary code as | root. Also see "APT-2026-11-01 security update." [4] Impact ------- An attacker who controls an update mirror or who can modify network traffic can attempt to exploit this vulnerability in order to compromise Debian and Whonix qubes.

Affected systems ----------------- Qubes OS systems containing Debian and Whonix qubes are affected. Qubes OS systems containing only Fedora (or other non-APT-based) qubes are not affected. Discussion ----------- By default, the Advanced Package Tool (APT) verifies downloaded packages via signed repository metadata.

This allows for using package repositories without having to trust the server hosting them or the transport method used to download them. The vulnerability under discussion breaks this mechanism. An attacker who successfully exploits this vulnerability can manipulate the packages that APT downloads and installs, potentially leading to complete compromise of the affected qube.

A successful attack requires one or more of the following: - The attacker controls the server on which the repository is hosted (e.g., a third-party mirror). - The transport mechanism is not authenticated (e.g., plain HTTP), and the attacker can tamper with the connection to the server. - An independent vulnerability allows the attacker to achieve one of the above (e.g., exploiting a bug in the server or compromising a trusted certificate authority (CA) or a digital certificate issued by such an authority). In Qubes OS, Debian and Whonix qubes use HTTPS for APT repositories by default, which eliminates the second (man-in-the-middle) attack vector. (Users who have manually changed their configurations to use plain HTTP for any repositories are still affected. Users who have manually installed unofficial APT-based qubes besides Debian and Whonix are also affected.) Normally, we do not release Qubes security bulletins (QSBs) to address vulnerabilities that affect qubes only internally without affecting the rest of Qubes OS, since such vulnerabilities do not undermine the Qubes security model. (On the contrary, the security model is built on the assumption that such vulnerabilities are inevitable.) However, the vulnerability under discussion is somewhat special.

While it affects qubes only internally, it could allow an attacker to compromise templates, which are used as a basis for creating other qubes, such as app and service qubes. If a template is compromised, then all the qubes based on that template will also be compromised. App qubes operate directly on user data, and service qubes can affect user privacy (e.g., Whonix and VPN proxy qubes).

In Qubes OS, we take special precautions to make templates difficult to compromise. For example, we block all network connections to and from templates, with one exception: We allow templates to connect to an "update proxy" that allows the template to retrieve updates while protecting users from accidentally using templates to perform risky activities, such as browsing the web. Since the vulnerability under discussion has the potential to subvert these defenses, and since we can address it via the Qubes update system, we've decided to issue this QSB and its attendant security updates.

Patching --------- The packages below contain security updates to the Qubes update tools that address the vulnerability described in this bulletin. After these updates are applied, the Qubes update tools will update APT in a safe way. For Qubes 4.3, in dom0: - qubes-core-dom0-linux 4.3.25 - qubes-mgmt-salt-dom0-update 4.3.4 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 should be installed as described in the "User action" section above.

Credits See the Debian and APT security advisories. [3][4] References [1] https://doc.qubes-os.org/en/latest/user/how-to-guides/how-to-update.html [2] https://doc.qubes-os.org/en/latest/user/downloading-installing-upgrading/testing.html [3] https://lists.debian.org/debian-security-announce/2026/msg00526.html [4] https://lists.debian.org/deity/2026/11/msg00005.html -- The Qubes Security Team Marek Marczykowski-Górecki’s PGP signature -----BEGIN PGP SIGNATURE----- iQIzBAABCAAdFiEELRdx/k12ftx2sIn61lWk8hgw4GoFAmrtJOsACgkQ1lWk8hgw 4Gr4dA/+J3brLV8sxzHtTP/6YxiNXEaLLcq1QLQ8NMuRpo2+zzHT+L16sHYoSiv9 gPiDRJmrQhZEo4WJrjgYSn/VGqcuG4GvZduuNLQJfEw5CZ1jBzE5mmUgI92wth9M gY2UpzKMp95k+dZEMWl7RZwhs6aT5Sld9O4D4qSlpZpl06iZ6+kX7g0LpCa+Dh/P 8ACo3cjwkiRi3oQos6AIe+oM0ET2iB8cycTwArqn6xgj31HtpF8dhlSK5UiePgfV 4JoWaNthMsu3DTvGmee91jMUXYlEPbChTt8wYlRZEwO6fyYYzGooEbj265W9nB32 w8W2KNWY0ydNOwOgSNqljk8bJymZqMjErzZJJtND5M5eeIzKQJnRtEjgyNKzN5jN +ooLUOYnFDtOThC0AEflngWPbcWmFbOdWwgbL/qHM8ijhT8TS4MPkukw38R6Skb3 1/xS2hFqUgT5BFlYmnpfBudH0R4KrnG86RetA2gzX9FfCI7l/k8frGkK0NvxsBAE 8G0WbtRBtX9htCsDVVYcDIfaIol7Xvx56mQVEf65MCAFoprJX9NUihFx5QH1uV5i Pxea8r7jXEKJ6DPnHZpPAUN4Xil7ypfGamYEhayjtUBWWgB8xtzQhnuqNKF6HlSH MGp/o/wdnRuSpTFoXCNQTPHpFwX0rAzo/qm0cc8hHP8YPgI4Okg= =mtb+ Simon Gaiser (aka HW42)’s PGP signature iQIzBAABCgAdFiEE6hjn8EDEHdrv6aoPSsGN4REuFJAFAmrtL5oACgkQSsGN4REu FJBKhA//YYHZVnYZG1e3mDBIrr6E8gtKC3b3snZxDoVuikpQbvB5eWaGXfnabOKi hoJnC9whJ3iqHwcM74cZz3S63ech+uywNYQxpjR40OHwNXUSwtlRMFlmXQVhHG4L ejn5xUO373IZGzqFzmlTpYqvHYLE6XqkQRhFTXNBK2w2KeqofkYcU2EI61FWXqaw N12ojrfqYmWGpjndGguA4eax3Ss+zOjiyVKrMMh6A8hAeRNSXuV70hzcEEmPeS4B IFLIUqanVD6mp+69wwh0JGlB57FinQ3QrIWX8iWYhOWEqJ5wpB47f/vzJIMDSsk5 wnnuY0zac0AbqMkByscrzp3eF+cnrzyTZ3BPwhu+xi+6uY3VVaTB6m7b5UMnl8z3 ov/3MnsdUKKUbGgvz+TjW8q1opdAnH1WifjbqIQcMkbdoz3NLnVhJjaitnoma5eW 2CMQsvp5V8OVHYVE2frzNZlmV9xs/Q5V9WxdGyk+L2paZYykHNOGIY35wFomIwQC iQlFa4dDsHQaqosXz19rM6hwFqdmOmJDfwv9r1tddnqPKQjr9YVhX6/cLd18NTAq cYLO2b3I6KXifKXLD3oWqgNxN9b/XAAwTQRKthSNBQ/rYUK/0jwDMTcPdWGpVeWc VCcJ3Rtvn46qs8o0+7Ih6Gi0UsYMUkE1RjtPqKlatGb8YIxM5x8= 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. 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 git and gpg installed. (For Windows and Mac options, see OpenPGP software.) 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 (For more ways to obtain the QMSK, see How to import and authenticate the Qubes Master Signing Key.) 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.

For more information, see 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. Once you are satisfied that you have the genuine QMSK, set its trust level to 5 (“ultimate”), then quit GnuPG with q. gpg> trust 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 trust: ultimate validity: unknown 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: 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: 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 --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 --verify canary-034-2023.txt.sig.simon canary-034-2023.txt gpg: Signature made Thu 02 Mar 2023 01:47:52 AM PST 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-122), the commands are: $ gpg --verify qsb-122-2026.txt.sig.marmarek qsb-122-2026.txt $ gpg --verify qsb-122-2026.txt.sig.simon qsb-122-2026.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-122 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.