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

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-10 · updated 2026-10-19
• Weakness: CWE-191

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.

Affected products

• Linux kernel: 4.8 — fixed in 7.2

How to fix

Upgrade to a fixed version: Linux kernel 7.2. Check the vendor advisory for mitigations.

References

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

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