CVE-2026-43067

Description

In the Linux kernel, the following vulnerability has been resolved: ext4: handle wraparound when searching for blocks for indirect mapped blocks Commit 4865c768b563 ("ext4: always allocate blocks only from groups inode can use") restricts what blocks will be allocated for indirect block based files to block numbers that fit within 32-bit block numbers. However, when using a review bot running on the latest Gemini LLM to check this commit when backporting into an LTS based kernel, it raised this concern: If ac->ac_g_ex.fe_group is >= ngroups (for instance, if the goal group was populated via stream allocation from s_mb_last_groups), then start will be >= ngroups. Does this allow allocating blocks beyond the 32-bit limit for indirect block mapped files? The commit message mentions that ext4_mb_scan_groups_linear() takes care to not select unsupported groups. However, its loop uses group = *start, and the very first iteration will call ext4_mb_scan_group() with this unsupported group because next_linear_group() is only called at the end of the iteration. After reviewing the code paths involved and considering the LLM review, I determined that this can happen when there is a file system where some files/directories are extent-mapped and others are indirect-block mapped. To address this, add a safety clamp in ext4_mb_scan_groups().

Gravité et risque d'exploitation

CVE-2026-43067 obtient un score CVSS de 9.8/10, soit une gravité critique. Selon le modèle EPSS, la probabilité qu'elle soit exploitée dans les 30 prochains jours est de 0.72 %, ce qui la place devant 53.1 % des CVE référencées.

Que faire ?

• Vérifiez si Linux (versions <2a368ccddfc492a0aa951e2caef2985f20e96503, <12624c5b724a81e14e532972b40d863b0de3b7d1, 1b0edd6022a3f44ce87fea9959a9310f4628fbea, 9d89b9d55e25cb340c5b4b769876edc551b7a9ff, 34c803edc0b3365a42efcf9815acab63b4cf54e0, <6.1.168, 16fce6b6c0b247258c6c217fce5a48abf50f6964, 321ed8d559c951e71ad2d2d69a4cf0445644e865, 5.15.203, <f89bba144938921a2249237ad04a0183ff3f8930, <5.16, <83170a05908b6cf2fb3235d3065bf613ff866f3c, <6.6.134, <6.12.80, 9eea2f57d11b30049ff996ac3eff6e0dc8089e5f, 6.1.167, <bb81702370fad22c06ca12b6e1648754dbc37e0f, <4bec4a498ce86314d470ae6144120461f2138c29, 6.19.4, <6.19.11, 6.12.77, <6.18.21, 4865c768b563deff1b6a6384e74a62f143427b42, 6.6.130, 6.18.14) 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.

Références

• https://git.kernel.org/stable/c/f89bba144938921a2249237ad04a0183ff3f8930
• https://git.kernel.org/stable/c/83170a05908b6cf2fb3235d3065bf613ff866f3c
• https://git.kernel.org/stable/c/4bec4a498ce86314d470ae6144120461f2138c29
• https://git.kernel.org/stable/c/12624c5b724a81e14e532972b40d863b0de3b7d1
• https://git.kernel.org/stable/c/2a368ccddfc492a0aa951e2caef2985f20e96503
• https://git.kernel.org/stable/c/bb81702370fad22c06ca12b6e1648754dbc37e0f