CVE-2026-31788 (GCVE-0-2026-31788)

Vulnerability from cvelistv5 – Published: 2026-03-25 10:25 – Updated: 2026-04-02 14:44
VLAI?
Title
xen/privcmd: restrict usage in unprivileged domU
Summary
In the Linux kernel, the following vulnerability has been resolved: xen/privcmd: restrict usage in unprivileged domU The Xen privcmd driver allows to issue arbitrary hypercalls from user space processes. This is normally no problem, as access is usually limited to root and the hypervisor will deny any hypercalls affecting other domains. In case the guest is booted using secure boot, however, the privcmd driver would be enabling a root user process to modify e.g. kernel memory contents, thus breaking the secure boot feature. The only known case where an unprivileged domU is really needing to use the privcmd driver is the case when it is acting as the device model for another guest. In this case all hypercalls issued via the privcmd driver will target that other guest. Fortunately the privcmd driver can already be locked down to allow only hypercalls targeting a specific domain, but this mode can be activated from user land only today. The target domain can be obtained from Xenstore, so when not running in dom0 restrict the privcmd driver to that target domain from the beginning, resolving the potential problem of breaking secure boot. This is XSA-482 --- V2: - defer reading from Xenstore if Xenstore isn't ready yet (Jan Beulich) - wait in open() if target domain isn't known yet - issue message in case no target domain found (Jan Beulich)
Severity ?
8.2 (High)
CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 1c5de1939c204bde9cce87f4eb3d26e9f9eb732b , < 87a803edb2ded911cb587c53bff179d2a2ed2a28 (git)
Affected: 1c5de1939c204bde9cce87f4eb3d26e9f9eb732b , < 1879319d790f7d57622cdc22807b60ea78b56b6d (git)
Affected: 1c5de1939c204bde9cce87f4eb3d26e9f9eb732b , < 78432d8f0372c71c518096395537fa12be7ff24e (git)
Affected: 1c5de1939c204bde9cce87f4eb3d26e9f9eb732b , < 389bae9a4409934e8b8d4dbdaaf02a3ae71cf8e4 (git)
Affected: 1c5de1939c204bde9cce87f4eb3d26e9f9eb732b , < cbede2e833da1893afbea9b3ff29b5dda23a4a91 (git)
Affected: 1c5de1939c204bde9cce87f4eb3d26e9f9eb732b , < 453b8fb68f3641fea970db88b7d9a153ed2a37e8 (git)
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    Linux Linux Affected: 2.6.37
Unaffected: 0 , < 2.6.37 (semver)
Unaffected: 6.1.167 , ≤ 6.1.* (semver)
Unaffected: 6.6.130 , ≤ 6.6.* (semver)
Unaffected: 6.12.78 , ≤ 6.12.* (semver)
Unaffected: 6.18.20 , ≤ 6.18.* (semver)
Unaffected: 6.19.10 , ≤ 6.19.* (semver)
Unaffected: 7.0-rc6 , ≤ * (original_commit_for_fix)
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Esto normalmente no es un problema, ya que el acceso suele estar limitado a root y el hipervisor denegar\u00e1 cualquier hiperllamada que afecte a otros dominios.\\n\\nEn caso de que el invitado se inicie usando arranque seguro, sin embargo, el controlador privcmd estar\u00eda permitiendo que un proceso de usuario root modifique, por ejemplo, el contenido de la memoria del kernel, rompiendo as\u00ed la caracter\u00edstica de arranque seguro.\\n\\nEl \u00fanico caso conocido en el que un domU no privilegiado realmente necesita usar el controlador privcmd es el caso en el que act\u00faa como modelo de dispositivo para otro invitado. En este caso, todas las hiperllamadas emitidas a trav\u00e9s del controlador privcmd se dirigir\u00e1n a ese otro invitado.\\n\\nAfortunadamente, el controlador privcmd ya puede ser bloqueado para permitir solo hiperllamadas dirigidas a un dominio espec\u00edfico, pero este modo solo puede activarse desde el espacio de usuario hoy.\\n\\nEl dominio objetivo puede obtenerse de Xenstore, por lo que cuando no se ejecute en dom0, restrinja el controlador privcmd a ese dominio objetivo desde el principio, resolviendo el problema potencial de romper el arranque seguro.\\n\\nEsto es XSA-482\\n\\n---\\nV2:\\n- aplazar la lectura de Xenstore si Xenstore a\u00fan no est\u00e1 listo (Jan Beulich)\\n- esperar en open() si el dominio objetivo a\u00fan no se conoce\\n- emitir mensaje en caso de no encontrar dominio objetivo (Jan Beulich)\"}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H\",\"baseScore\":8.2,\"baseSeverity\":\"HIGH\",\"attackVector\":\"LOCAL\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"HIGH\",\"userInteraction\":\"NONE\",\"scope\":\"CHANGED\",\"confidentialityImpact\":\"HIGH\",\"integrityImpact\":\"HIGH\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":1.5,\"impactScore\":6.0}]},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/1879319d790f7d57622cdc22807b60ea78b56b6d\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/389bae9a4409934e8b8d4dbdaaf02a3ae71cf8e4\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/453b8fb68f3641fea970db88b7d9a153ed2a37e8\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/78432d8f0372c71c518096395537fa12be7ff24e\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/87a803edb2ded911cb587c53bff179d2a2ed2a28\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/cbede2e833da1893afbea9b3ff29b5dda23a4a91\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"http://www.openwall.com/lists/oss-security/2026/03/24/2\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\"},{\"url\":\"http://www.openwall.com/lists/oss-security/2026/03/24/3\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\"},{\"url\":\"http://www.openwall.com/lists/oss-security/2026/03/24/4\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\"},{\"url\":\"http://www.openwall.com/lists/oss-security/2026/03/24/5\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\"},{\"url\":\"http://www.openwall.com/lists/oss-security/2026/03/26/4\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\"},{\"url\":\"http://xenbits.xen.org/xsa/advisory-482.html\",\"source\":\"af854a3a-2127-422b-91ae-364da2661108\"}]}}"
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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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