CVE-2026-68123
Received Received - Intake

Openvswitch GSO Truncation Underflow Vulnerability

Publication date: 2026-08-10

Last updated on: 2026-08-10

Assigner: kernel.org

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.

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Meta Information

Published
2026-08-10
Last Modified
2026-08-10
Generated
2026-08-10
AI Q&A
2026-08-10
EPSS Evaluated
N/A
NVD
CVE-2026-68123
EUVD
EUVD-2026-55504

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
openvswitch openvswitch *

Helpful Resources

Exploitability

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KEV
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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability in the Linux kernel involves a flaw in Open vSwitch (OVS) where the GSO userspace truncation underflow occurs. The issue arises when OVS_ACTION_ATTR_TRUNC stores a delta from the original skb length, which is then incorrectly reused for smaller segments of a GSO skb. This can lead to a situation where the segment's cutlen exceeds the skb length, causing an underflow in the length passed to skb_zerocopy().

Detection Guidance

This vulnerability is specific to the Linux kernel's Open vSwitch (OVS) implementation. Detection requires checking if your system is running a vulnerable kernel version with OVS enabled. Use commands like 'uname -a' to check the kernel version and 'lsmod | grep openvswitch' to verify if OVS modules are loaded.

Impact Analysis

This vulnerability could allow an attacker to cause a denial of service or potentially execute arbitrary code by exploiting the underflow in skb_zerocopy(). Systems using Open vSwitch with GSO (Generic Segmentation Offload) enabled may be affected, leading to crashes or instability.

Mitigation Strategies

Apply the latest kernel update that includes the fix for this OVS truncation underflow issue. If immediate patching is not possible, consider disabling OVS or restricting its use until the update is applied.

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