CVE-2026-89775
Vulnérabilité critique dans Linux (Linux)
Description
In the Linux kernel, the following vulnerability has been resolved: KVM: arm64: Handle negative S1 walk levels in VNCR TLB size evaluation Computing the effects of a TLB invalidation involves looking at the size of the mapping cached by the TLB. For S1 mappings such as VNCR, this is deducted from the combination of the base granule size and the mapping level. However, this implies that the S1 MMU is *on*. When the MMU is off, we indicate this with the level being set to a "creative" value of -127 (S1_MMU_DISABLED). This ends-up being misinterpreted by pgshift_level_to_ttl() as it doesn't handle negative levels at all (the level is immediately cast to a u8 and only the bottom two bits considered), leading to an invalidation size of 0. Not helpful. Tidy-up pgshift_level_to_ttl() to handle these negative levels, and ttl_to_size() to always return SZ_1G when no valid TTL is present. This allows the removal of open-coded checks for similar situations. Note that the check for a negative value not explicitely checking for S1_MMU_DISABLED is deliberate, so that actual negative levels introduced with LVA2 and D128 can take the same path if we ever support them.
Gravité et risque d'exploitation
CVE-2026-89775 obtient un score CVSS de 9.3/10, soit une gravité critique. Selon le modèle EPSS, la probabilité qu'elle soit exploitée dans les 30 prochains jours est de 0.23 %, ce qui la place devant 12.9 % des CVE référencées.
Que faire ?
- Vérifiez si Linux (versions <6.16, 6.18.51, 7270cc9157f474dfc46750a34c9d7defc686b2eb, <=*, 6.16, <=7.2.*, <=6.18.*, 7.2.5, <1c9fca34b9625a67a7f1a03c8604f3df760c6c49, <be54a70067c7dbe1381157e8a238fa4b16ea9c05, 0, <8053393680d4fa3eb962667d2be95dd39f0940e5, 7.3) est présent sur votre parc.
- Appliquez le correctif ou la version corrigée indiqués dans les références de l'éditeur.
- À défaut de correctif, limitez l'exposition (filtrage réseau, désactivation du composant).
- Automatisez la détection : les agents CVE Heimdall (gratuits, open source) corrèlent l'inventaire de vos serveurs avec la base CVE.