{"id":"CVE-2026-13478","summary":"Out-of-bounds read in Zephyr ext2 block-bitmap validation from a crafted s_blocks_count","details":"The Zephyr ext2 filesystem driver validates the on-disk block bitmap in ext2_init_fs() (subsys/fs/ext2/ext2_impl.c) by passing fs_blocks = s_blocks_count - s_first_data_block to ext2_bitmap_count_set(). That helper (subsys/fs/ext2/ext2_bitmap.c) treats its argument as a number of bits and reads one bitmap byte per eight bits, but the bitmap buffer (BGROUP_BLOCK_BITMAP) is a single fetched block of only fs-\u003eblock_size bytes (capacity fs-\u003eblock_size * 8 bits). s_blocks_count and s_first_data_block are taken verbatim from the superblock and were never bounded against this single-group capacity; ext2_verify_disk_superblock() checks the magic, revision, and block-size shift but not the block count.\n\nA crafted ext2 image with an oversized s_blocks_count (up to ~4 billion, against a maximum 4096-byte block / 32768-bit bitmap) makes ext2_bitmap_count_set() scan roughly 512 MB of memory past the bitmap block — a large out-of-bounds read of the static block slab and adjacent memory.\n\nThe defect is reached during mount: ext2_init_fs() is invoked from ext2_mount() (subsys/fs/ext2/ext2_ops.c), the registered .mount operation. Any path that mounts an attacker-supplied ext2 image (removable media, a disk/flash partition, or a downloaded image) triggers it. The kernel-privileged parser operates on attacker-controlled data, so the bug is exploitable wherever untrusted ext2 media can be mounted.\n\nImpact is an out-of-bounds read only: the resulting bit count is compared internally and the mount is rejected, so no attacker-controlled bytes are returned (not a useful information leak). The ~512 MB over-read will almost certainly cross an unmapped or MPU-protected boundary and fault, crashing the system — a denial of service triggered by mounting a single malformed image. The fix rejects any image whose fs_blocks exceeds fs-\u003eblock_size * 8 before the scan.","aliases":["GHSA-gj29-7f7m-4c29"],"modified":"2026-08-28T14:32:48.540559Z","published":"2026-08-25T16:05:39.217Z","database_specific":{"cna_assigner":"zephyr","cwe_ids":["CWE-125"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/13xxx/CVE-2026-13478.json"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/13xxx/CVE-2026-13478.json"},{"type":"ADVISORY","url":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-gj29-7f7m-4c29"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-13478"},{"type":"FIX","url":"https://github.com/zephyrproject-rtos/zephyr/commit/9c0f869da07009d9d4bca7a99e995f9b8cea7da2"},{"type":"PACKAGE","url":"https://github.com/zephyrproject-rtos/zephyr"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/zephyrproject-rtos/zephyr","events":[{"introduced":"a6eef0ba3755f2530c5ce93524e5ac4f5be30194"},{"fixed":"9c0f869da07009d9d4bca7a99e995f9b8cea7da2"}],"database_specific":{"extracted_events":[{"introduced":"3.5.0"},{"fixed":"4.4.2"}],"source":["AFFECTED_FIELD","REFERENCES"]}}],"versions":["v4.4.0","v4.4.0-rc3","v4.4.0-rc2","v4.4.0-rc1","v4.3.0","v4.3.0-rc3","v4.3.0-rc2","v4.3.0-rc1","v4.2.0","v4.2.0-rc3","v4.2.0-rc2","v4.2.0-rc1","v4.1.0","v4.1.0-rc3","v4.1.0-rc2","v4.1.0-rc1","v4.0.0","v4.0.0-rc3","v4.0.0-rc2","v4.0.0-rc1","v3.7.0","v3.7.0-rc3","v3.7.0-rc2","v3.7.0-rc1","v3.6.0","v3.6.0-rc3","v3.6.0-rc2","v3.6.0-rc1","zephyr-v3.5.0","v3.5.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-13478.json","vanir_signatures_modified":"2026-08-28T14:32:48Z","vanir_signatures":[{"source":"https://github.com/zephyrproject-rtos/zephyr/commit/9c0f869da07009d9d4bca7a99e995f9b8cea7da2","target":{"file":"subsys/fs/ext2/ext2_impl.c"},"deprecated":false,"digest":{"line_hashes":["237063317660053419602987038656785327412","289860565528130145462671730229321039800","21575920350590289610715143231250589447"],"threshold":0.9},"id":"CVE-2026-13478-71ff6495","signature_type":"Line","signature_version":"v1"},{"signature_version":"v1","source":"https://github.com/zephyrproject-rtos/zephyr/commit/9c0f869da07009d9d4bca7a99e995f9b8cea7da2","target":{"file":"subsys/fs/ext2/ext2_impl.c","function":"ext2_init_fs"},"deprecated":false,"digest":{"function_hash":"229993982260619983220957148204655967385","length":1122},"id":"CVE-2026-13478-ebdbdfe5","signature_type":"Function"}]}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"}]}