What’s Vulnerable › Vulnerabilities

CVE-2026-98621: net: gue: reject invalid REMCSUM offsets

• Severity: unknown
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-18 · updated 2026-10-19

Description

In the Linux kernel, the following vulnerability has been resolved: net: gue: reject invalid REMCSUM offsets The REMCSUM option carries an absolute checksum start and checksum field offset. gue_remcsum() passes them to skb_remcsum_process(), whose partial path stores offset - start in the u16 skb->csum_offset variable. If offset is less than start, this underflows. A forwarded packet can retain CHECKSUM_PARTIAL and reach a NETIF_F_HW_CSUM driver which trusts the metadata, leading skb_copy_and_csum_dev() to write two bytes about 64 KiB beyond the destination buffer. Reject reversed tuples in validate_gue_flags(), after the existing length validation, so all GUE parsers enforce the ordering in one place.

Affected products

• Linux kernel: 4.0 — fixed in 7.3

How to fix

Upgrade to a fixed version: Linux kernel 7.3. Check the vendor advisory for mitigations.

References

• https://git.kernel.org/stable/c/1d664be4ca49d1696e85239236f4988dfc4653c3
• https://git.kernel.org/stable/c/1eeec0c51fd5598da44080ed96bbd9880021c28b
• https://git.kernel.org/stable/c/2566866fc30965d915d0b52b5c3323b362619f0e
• https://git.kernel.org/stable/c/40aeafbcbc7bc4018e8f74bbbb4d29ed8846f57f
• https://git.kernel.org/stable/c/43efb1f997e976f386aa89716f55870cd2cff9ad
• https://git.kernel.org/stable/c/4b9bc21b2396c396d88dd909caaf73d5be6ff593
• https://git.kernel.org/stable/c/97f907203321eee2cc9132d5c9eb47698fb41d35
• https://git.kernel.org/stable/c/c20f755338ca234e523dfc943719f194dfc1f903

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