In the Linux kernel, the following vulnerability has been resolved:
tcp: ipv6: clamp default adverting MSS to avoid GSO_BY_FRAGS (0xFFFF)
When MTU is large, ip6_default_advmss() can return IPV6_MAXPLEN (65535). This is interpreted by TCP as mss_clamp, allowing the MSS to reach 65535.
However, 0xFFFF is also used as a magic value GSO_BY_FRAGS in the kernel. If a TCP packet with gso_size=0xFFFF is passed to skb_segment(), it will be mistakenly treated as GSO_BY_FRAGS, leading to a NULL pointer dereference because local TCP packets do not use frag_list.
Fix this by returning min(IPV6_MAXPLEN, GSO_BY_FRAGS - 1) (65534) from ip6_default_advmss() when MTU is large.
Also update the stale comment in ip6_default_advmss() which suggested that IPV6_MAXPLEN is returned to mean "any MSS".
CVSS Details
- CVSS 3.1 Base Score: 7.5
- CVSS 3.1 Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)
Covered by Rapid7
| Product | Vendor Advisory | Solution File | Added | Published |
|---|---|---|---|---|
| Amazon_linux_2023 | — | Upgrade kernel-tools-debuginfoUpgrade kernel-tools-develUpgrade kernel-modules-extraUpgrade python3-perfUpgrade bpftool-debuginfoUpgrade kernel-debuginfoUpgrade perf-debuginfoUpgrade perfUpgrade kernel-headersUpgrade bpftoolUpgrade python3-perf-debuginfoUpgrade kernelUpgrade kernel-debuginfo-common-aarch64Upgrade kernel-toolsUpgrade kernel-modules-extra-commonUpgrade kernel-livepatch-6.1.180-225.360Upgrade kernel-debuginfo-common-x86_64Upgrade kernel-devel | Sep 1, 2026 | Aug 15, 2026 |
| Debian | — | Upgrade linux | Aug 16, 2026 | Aug 16, 2026 |
| Redhat_linux | — | No solution exists | Aug 21, 2026 | Aug 15, 2026 |
| Vmware Photon_os | — | Use 'tdnf update' to upgrade all packages to the latest version. | Aug 21, 2026 | Aug 15, 2026 |
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