---
id: "CVE-2026-98879"
kind: "vulnerability"
aliases: ["CVE-2026-98879"]
title: "Linux kernel isofs: mounting oversized block sizes crashes the kernel"
severity: "unknown"
cvss: null
epss: 0.00215
exploited: false
status: "open"
category: "infrastructure"
products: []
ecosystems: []
tags: ["infrastructure", "isofs", "linux-kernel", "self-hosted"]
not_affected_if: ["no-isofs-mounts"]
published_at: "2026-10-23T12:18:21+00:00"
first_seen_at: "2026-10-23T21:57:33+00:00"
updated_at: "2026-10-25T12:38:51+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98879", "first_seen_at": "2026-10-23T21:57:33+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-98879", "first_seen_at": "2026-10-25T12:38:51+00:00"}]
---

# Linux kernel isofs: mounting oversized block sizes crashes the kernel

In the Linux kernel's isofs driver, a block size larger than the page size is not rejected cleanly when mounting, so the kernel hits a BUG_ON during the first buffer read. The sources describe a kernel crash at mount time, and do not say that an attacker can gain code execution or read data.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- `uname -r` to see the running kernel version
- Check whether isofs is loaded or available with `lsmod | grep isofs` or `modinfo isofs`
- unknown whether the sources list affected kernel version ranges

## Fix

- Update to a kernel release that includes the upstream isofs set_blocksize fix (version unknown from sources)
- unknown whether the sources name a specific fixed kernel version

## Timeline

- 2026-10-23T21:57:33+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98879
- 2026-10-25T12:38:51+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-98879

## From the sources

In the Linux kernel, the following vulnerability has been resolved:

isofs: handle set_blocksize failures

isofs uses buffer_heads, which don't handle block size > PAGE_SIZE well.
Without this, mounting we will hit the

        BUG_ON(offset >= folio_size(folio));

in folio_set_bh on the first __bread_gfp call.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_