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CVE-2025-39770 is an incorrect checksum-offload handling vulnerability in the Linux kernel networking stack. When Generic Segmentation Offload (GSO) processes an IPv6 packet containing extension headers, it can request checksum offload from an egress device advertising only NETIF_F_IPV6_CSUM. That feature supports plain TCP or UDP over IPv6, but not packets with extension headers. Although hardware TSO/USO is bypassed in favor of software segmentation, the incompatible checksum-offload request remains enabled. Traffic such as GRE-over-IPv6 can consequently trigger skb_warn_bad_offload warnings and collapse network throughput. The correction updates gso_features_check to mask incompatible offload features while preserving the BIG TCP extension-header exception.
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A Linux kernel networking flaw incorrectly requests unsupported checksum offloading for IPv6 packets containing extension headers, including traffic in GRE-over-IPv6 tunnels. It can severely degrade network throughput and availability. The reference assigns a CVSS v3 score of 5.5 and recommends updating Echo linux packages to version 6.1.153-1 or later.
A vulnerability referenced by the Red Hat kernel advisory; no technical details are provided in the supplied content.
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Cross-references every affected SKU, including bundled OEM variants.
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