# CVE-2026-23238: romfs: check sb_set_blocksize() return value CVE-2026-23238 is fixed in 23 products on 1 platform, first by DEBIAN-CVE-2026-23238, released March 4, 2026. It is not reported as exploited. Patch Radar priority: Routine. - Web page: https://patchblox.com/security/cve/CVE-2026-23238 - Priority: Routine - CVSS: 5.5 (Moderate) - EPSS: 0.0022 - CISA KEV: not listed - Exploited (vendor report): no - Publicly disclosed: no - Published: Mar 4, 2026 - Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-23238 ## Description In the Linux kernel, the following vulnerability has been resolved: romfs: check sb_set_blocksize() return value romfs_fill_super() ignores the return value of sb_set_blocksize(), which can fail if the requested block size is incompatible with the block device's configuration. This can be triggered by setting a loop device's block size larger than PAGE_SIZE using ioctl(LOOP_SET_BLOCK_SIZE, 32768), then mounting a romfs filesystem on that device. When sb_set_blocksize(sb, ROMBSIZE) is called with ROMBSIZE=4096 but the device has logical_block_size=32768, bdev_validate_blocksize() fails because the requested size is smaller than the device's logical block size. sb_set_blocksize() returns 0 (failure), but romfs ignores this and continues mounting. The superblock's block size remains at the device's logical block size (32768). Later, when sb_bread() attempts I/O with this oversized block size, it triggers a kernel BUG in folio_set_bh(): kernel BUG at fs/buffer.c:1582! BUG_ON(size > PAGE_SIZE); Fix by checking the return value of sb_set_blocksize() and failing the mount with -EINVAL if it returns 0. ## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Linux | bpftool amzn 2023 | 1:6.1.164-196.303.amzn2023 | [ALAS2023-2026-1491](https://patchblox.com/security/data/fix/linux/alas2023-2026-1491.md) | Mar 16, 2026 | | Linux | bpftool-debuginfo amzn 2023 | 1:6.1.164-196.303.amzn2023 | [ALAS2023-2026-1491](https://patchblox.com/security/data/fix/linux/alas2023-2026-1491.md) | Mar 16, 2026 | | Linux | kernel amzn 2023 | 1:6.1.164-196.303.amzn2023 | [ALAS2023-2026-1491](https://patchblox.com/security/data/fix/linux/alas2023-2026-1491.md) | Mar 16, 2026 | | Linux | kernel-debuginfo amzn 2023 | 1:6.1.164-196.303.amzn2023 | [ALAS2023-2026-1491](https://patchblox.com/security/data/fix/linux/alas2023-2026-1491.md) | Mar 16, 2026 | | Linux | kernel-debuginfo-common-aarch64 amzn 2023 | 1:6.1.164-196.303.amzn2023 | [ALAS2023-2026-1491](https://patchblox.com/security/data/fix/linux/alas2023-2026-1491.md) | Mar 16, 2026 | | Linux | kernel-debuginfo-common-x86_64 amzn 2023 | 1:6.1.164-196.303.amzn2023 | [ALAS2023-2026-1491](https://patchblox.com/security/data/fix/linux/alas2023-2026-1491.md) | Mar 16, 2026 | | Linux | kernel-devel amzn 2023 | 1:6.1.164-196.303.amzn2023 | [ALAS2023-2026-1491](https://patchblox.com/security/data/fix/linux/alas2023-2026-1491.md) | Mar 16, 2026 | | Linux | kernel-headers amzn 2023 | 1:6.1.164-196.303.amzn2023 | [ALAS2023-2026-1491](https://patchblox.com/security/data/fix/linux/alas2023-2026-1491.md) | Mar 16, 2026 | | Linux | kernel-libbpf amzn 2023 | 1:6.1.164-196.303.amzn2023 | [ALAS2023-2026-1491](https://patchblox.com/security/data/fix/linux/alas2023-2026-1491.md) | Mar 16, 2026 | | Linux | kernel-libbpf-debuginfo amzn 2023 | 1:6.1.164-196.303.amzn2023 | [ALAS2023-2026-1491](https://patchblox.com/security/data/fix/linux/alas2023-2026-1491.md) | Mar 16, 2026 | | Linux | kernel-libbpf-devel amzn 2023 | 1:6.1.164-196.303.amzn2023 | [ALAS2023-2026-1491](https://patchblox.com/security/data/fix/linux/alas2023-2026-1491.md) | Mar 16, 2026 | | Linux | kernel-libbpf-static amzn 2023 | 1:6.1.164-196.303.amzn2023 | [ALAS2023-2026-1491](https://patchblox.com/security/data/fix/linux/alas2023-2026-1491.md) | Mar 16, 2026 | | Linux | kernel-livepatch-6.1.164-196.303 amzn 2023 | 1:1.0-0.amzn2023 | [ALAS2023-2026-1491](https://patchblox.com/security/data/fix/linux/alas2023-2026-1491.md) | Mar 16, 2026 | | Linux | kernel-modules-extra amzn 2023 | 1:6.1.164-196.303.amzn2023 | [ALAS2023-2026-1491](https://patchblox.com/security/data/fix/linux/alas2023-2026-1491.md) | Mar 16, 2026 | | Linux | kernel-modules-extra-common amzn 2023 | 1:6.1.164-196.303.amzn2023 | [ALAS2023-2026-1491](https://patchblox.com/security/data/fix/linux/alas2023-2026-1491.md) | Mar 16, 2026 | | Linux | kernel-tools amzn 2023 | 1:6.1.164-196.303.amzn2023 | [ALAS2023-2026-1491](https://patchblox.com/security/data/fix/linux/alas2023-2026-1491.md) | Mar 16, 2026 | | Linux | kernel-tools-debuginfo amzn 2023 | 1:6.1.164-196.303.amzn2023 | [ALAS2023-2026-1491](https://patchblox.com/security/data/fix/linux/alas2023-2026-1491.md) | Mar 16, 2026 | | Linux | kernel-tools-devel amzn 2023 | 1:6.1.164-196.303.amzn2023 | [ALAS2023-2026-1491](https://patchblox.com/security/data/fix/linux/alas2023-2026-1491.md) | Mar 16, 2026 | | Linux | linux Debian 12.15 (bookworm) | 6.1.164-1 | [DEBIAN-CVE-2026-23238](https://patchblox.com/security/data/fix/linux/debian-cve-2026-23238.md) | Mar 4, 2026 | | Linux | linux Debian 13.5 (trixie) | 6.12.74-2 | [DEBIAN-CVE-2026-23238](https://patchblox.com/security/data/fix/linux/debian-cve-2026-23238.md) | Mar 4, 2026 | | Linux | linux Debian 14 | 6.18.13-1 | [DEBIAN-CVE-2026-23238](https://patchblox.com/security/data/fix/linux/debian-cve-2026-23238.md) | Mar 4, 2026 | | Linux | perf amzn 2023 | 1:6.1.164-196.303.amzn2023 | [ALAS2023-2026-1491](https://patchblox.com/security/data/fix/linux/alas2023-2026-1491.md) | Mar 16, 2026 | | Linux | perf-debuginfo amzn 2023 | 1:6.1.164-196.303.amzn2023 | [ALAS2023-2026-1491](https://patchblox.com/security/data/fix/linux/alas2023-2026-1491.md) | Mar 16, 2026 | | Linux | python3-perf amzn 2023 | 1:6.1.164-196.303.amzn2023 | [ALAS2023-2026-1491](https://patchblox.com/security/data/fix/linux/alas2023-2026-1491.md) | Mar 16, 2026 | | Linux | python3-perf-debuginfo amzn 2023 | 1:6.1.164-196.303.amzn2023 | [ALAS2023-2026-1491](https://patchblox.com/security/data/fix/linux/alas2023-2026-1491.md) | Mar 16, 2026 | --- Data as of 2026-11-09T07:25:28Z UTC. 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