{"id":"CVE-2026-43067","state":"PUBLISHED","title":"ext4: handle wraparound when searching for blocks for indirect mapped blocks","description":"In the Linux kernel, the following vulnerability has been resolved:\n\next4: handle wraparound when searching for blocks for indirect mapped blocks\n\nCommit 4865c768b563 (\"ext4: always allocate blocks only from groups\ninode can use\") restricts what blocks will be allocated for indirect\nblock based files to block numbers that fit within 32-bit block\nnumbers.\n\nHowever, when using a review bot running on the latest Gemini LLM to\ncheck this commit when backporting into an LTS based kernel, it raised\nthis concern:\n\n   If ac->ac_g_ex.fe_group is >= ngroups (for instance, if the goal\n   group was populated via stream allocation from s_mb_last_groups),\n   then start will be >= ngroups.\n\n   Does this allow allocating blocks beyond the 32-bit limit for\n   indirect block mapped files? The commit message mentions that\n   ext4_mb_scan_groups_linear() takes care to not select unsupported\n   groups. However, its loop uses group = *start, and the very first\n   iteration will call ext4_mb_scan_group() with this unsupported\n   group because next_linear_group() is only called at the end of the\n   iteration.\n\nAfter reviewing the code paths involved and considering the LLM\nreview, I determined that this can happen when there is a file system\nwhere some files/directories are extent-mapped and others are\nindirect-block mapped.  To address this, add a safety clamp in\next4_mb_scan_groups().","publishedAt":"2026-05-05T15:23:26.717Z","updatedAt":"2026-10-19T19:06:12.380Z","severity":{"score":9.8,"label":"Critical","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"9d89b9d55e25cb340c5b4b769876edc551b7a9ff","status":"affected","lessThan":"f89bba144938921a2249237ad04a0183ff3f8930","versionType":"git"},{"version":"1b0edd6022a3f44ce87fea9959a9310f4628fbea","status":"affected","lessThan":"83170a05908b6cf2fb3235d3065bf613ff866f3c","versionType":"git"},{"version":"9eea2f57d11b30049ff996ac3eff6e0dc8089e5f","status":"affected","lessThan":"4bec4a498ce86314d470ae6144120461f2138c29","versionType":"git"},{"version":"34c803edc0b3365a42efcf9815acab63b4cf54e0","status":"affected","lessThan":"12624c5b724a81e14e532972b40d863b0de3b7d1","versionType":"git"},{"version":"321ed8d559c951e71ad2d2d69a4cf0445644e865","status":"affected","lessThan":"2a368ccddfc492a0aa951e2caef2985f20e96503","versionType":"git"},{"version":"4865c768b563deff1b6a6384e74a62f143427b42","status":"affected","lessThan":"bb81702370fad22c06ca12b6e1648754dbc37e0f","versionType":"git"},{"version":"16fce6b6c0b247258c6c217fce5a48abf50f6964","status":"affected","versionType":"git"},{"version":"5.15.203","status":"affected","lessThan":"5.16","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/ext4/mballoc.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"6.1.167","status":"affected","lessThan":"6.1.168","versionType":"semver"},{"version":"6.6.130","status":"affected","lessThan":"6.6.134","versionType":"semver"},{"version":"6.12.77","status":"affected","lessThan":"6.12.80","versionType":"semver"},{"version":"6.18.14","status":"affected","lessThan":"6.18.21","versionType":"semver"},{"version":"6.19.4","status":"affected","lessThan":"6.19.11","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/ext4/mballoc.c"]}],"references":["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"],"weaknesses":["CWE-822"],"ingestedAt":"2026-10-29T20:11:57.932Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/43xxx/CVE-2026-43067.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-43067","state":"PUBLISHED","datePublished":"2026-05-05T15:23:26.717Z","dateUpdated":"2026-10-19T19:06:12.380Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-05-01T14:12:55.981Z"},"containers":{"cna":{"title":"ext4: handle wraparound when searching for blocks for indirect mapped blocks","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\next4: handle wraparound when searching for blocks for indirect mapped blocks\n\nCommit 4865c768b563 (\"ext4: always allocate blocks only from groups\ninode can use\") restricts what blocks will be allocated for indirect\nblock based files to block numbers that fit within 32-bit block\nnumbers.\n\nHowever, when using a review bot running on the latest Gemini LLM to\ncheck this commit when backporting into an LTS based kernel, it raised\nthis concern:\n\n   If ac->ac_g_ex.fe_group is >= ngroups (for instance, if the goal\n   group was populated via stream allocation from s_mb_last_groups),\n   then start will be >= ngroups.\n\n   Does this allow allocating blocks beyond the 32-bit limit for\n   indirect block mapped files? The commit message mentions that\n   ext4_mb_scan_groups_linear() takes care to not select unsupported\n   groups. However, its loop uses group = *start, and the very first\n   iteration will call ext4_mb_scan_group() with this unsupported\n   group because next_linear_group() is only called at the end of the\n   iteration.\n\nAfter reviewing the code paths involved and considering the LLM\nreview, I determined that this can happen when there is a file system\nwhere some files/directories are extent-mapped and others are\nindirect-block mapped.  To address this, add a safety clamp in\next4_mb_scan_groups()."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"9d89b9d55e25cb340c5b4b769876edc551b7a9ff","status":"affected","lessThan":"f89bba144938921a2249237ad04a0183ff3f8930","versionType":"git"},{"version":"1b0edd6022a3f44ce87fea9959a9310f4628fbea","status":"affected","lessThan":"83170a05908b6cf2fb3235d3065bf613ff866f3c","versionType":"git"},{"version":"9eea2f57d11b30049ff996ac3eff6e0dc8089e5f","status":"affected","lessThan":"4bec4a498ce86314d470ae6144120461f2138c29","versionType":"git"},{"version":"34c803edc0b3365a42efcf9815acab63b4cf54e0","status":"affected","lessThan":"12624c5b724a81e14e532972b40d863b0de3b7d1","versionType":"git"},{"version":"321ed8d559c951e71ad2d2d69a4cf0445644e865","status":"affected","lessThan":"2a368ccddfc492a0aa951e2caef2985f20e96503","versionType":"git"},{"version":"4865c768b563deff1b6a6384e74a62f143427b42","status":"affected","lessThan":"bb81702370fad22c06ca12b6e1648754dbc37e0f","versionType":"git"},{"version":"16fce6b6c0b247258c6c217fce5a48abf50f6964","status":"affected","versionType":"git"},{"version":"5.15.203","status":"affected","lessThan":"5.16","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/ext4/mballoc.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"6.1.167","status":"affected","lessThan":"6.1.168","versionType":"semver"},{"version":"6.6.130","status":"affected","lessThan":"6.6.134","versionType":"semver"},{"version":"6.12.77","status":"affected","lessThan":"6.12.80","versionType":"semver"},{"version":"6.18.14","status":"affected","lessThan":"6.18.21","versionType":"semver"},{"version":"6.19.4","status":"affected","lessThan":"6.19.11","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/ext4/mballoc.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/f89bba144938921a2249237ad04a0183ff3f8930"},{"url":"https://git.kernel.org/stable/c/83170a05908b6cf2fb3235d3065bf613ff866f3c"},{"url":"https://git.kernel.org/stable/c/4bec4a498ce86314d470ae6144120461f2138c29"},{"url":"https://git.kernel.org/stable/c/12624c5b724a81e14e532972b40d863b0de3b7d1"},{"url":"https://git.kernel.org/stable/c/2a368ccddfc492a0aa951e2caef2985f20e96503"},{"url":"https://git.kernel.org/stable/c/bb81702370fad22c06ca12b6e1648754dbc37e0f"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","baseScore":9.8,"baseSeverity":"CRITICAL"},"scenarios":[{"lang":"en","value":"AV:N - In a reasonable high-impact deployment, a writable ext4 filesystem can be exported by in-kernel NFS or ksmbd, whose WRITE handlers enter the same VFS/ext4 allocation path. Local writes also reach it, but network is the highest defensible vector for an exported writable share.\nAC:L - Once the affected large mixed-format ext4 filesystem state exists, triggering is a normal file allocation/write path with no race or probabilistic memory condition. The attacker can drive stream allocation and indirect-file allocation through repeated writes.\nPR:N - A writable anonymous or guest NFS/SMB export can reach the vulnerable write path without local credentials or kernel capabilities. Even locally, only ordinary write permission to an affected file is needed, not administrative privilege.\nUI:N - No victim action is required after the vulnerable filesystem/share is available. The attacker triggers allocation directly by writing data.\nS:U - The impact remains within the kernel/filesystem security authority. This is not a VM escape, IOMMU bypass, or cross-authority sandbox escape.\nC:H - The bug can allocate a physical block above the 32-bit indirect-block limit and then store it through a 32-bit indirect pointer, wrapping the file mapping to another on-disk block. That can expose arbitrary file data from the same filesystem through the attacker's file.\nI:H - The wrapped indirect pointer can make attacker writes target blocks that were not actually allocated to the file. This can overwrite other file data or corrupt the filesystem.\nA:H - Filesystem corruption can make data unavailable and can force ext4 errors or read-only/remediation states. Repeated writes can reliably recreate the corruption on an affected deployment."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-05T12:25:42.475Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.1.167","versionEndExcluding":"6.1.168"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.6.130","versionEndExcluding":"6.6.134"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.12.77","versionEndExcluding":"6.12.80"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.18.14","versionEndExcluding":"6.18.21"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.19.4","versionEndExcluding":"6.19.11"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.15.203"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-43067","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T15:14:16.994971Z"}}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-822","lang":"en","type":"CWE","description":"CWE-822 Untrusted Pointer Dereference"}]}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-19T19:06:12.380Z"}}]}}}