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Fencer Vulns
high 7.5

CVE-2025-39770 json

net: gso: Forbid IPv6 TSO with extensions on devices with only IPV6_CSUM

published 2025-09-11 13 mo ago modified 2026-10-19 20 d ago also EUVD-2025-28942

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 31%
public exploits
0
none known

Summary

In the Linux kernel, the following vulnerability has been resolved:

net: gso: Forbid IPv6 TSO with extensions on devices with only IPV6_CSUM

When performing Generic Segmentation Offload (GSO) on an IPv6 packet that contains extension headers, the kernel incorrectly requests checksum offload if the egress device only advertises NETIF_F_IPV6_CSUM feature, which has a strict contract: it supports checksum offload only for plain TCP or UDP over IPv6 and explicitly does not support packets with extension headers. The current GSO logic violates this contract by failing to disable the feature for packets with extension headers, such as those used in GREoIPv6 tunnels.

This violation results in the device being asked to perform an operation it cannot support, leading to a `skb_warn_bad_offload` warning and a collapse of network throughput. While device TSO/USO is correctly bypassed in favor of software GSO for these packets, the GSO stack must be explicitly told not to request checksum offload.

Mask NETIF_F_IPV6_CSUM, NETIF_F_TSO6 and NETIF_F_GSO_UDP_L4 in gso_features_check if the IPv6 header contains extension headers to compute checksum in software.

The exception is a BIG TCP extension, which, as stated in commit 68e068cabd2c6c53 ("net: reenable NETIF_F_IPV6_CSUM offload for BIG TCP packets"): "The feature is only enabled on devices that support BIG TCP TSO. The header is only present for PF_PACKET taps like tcpdump, and not transmitted by physical devices."

kernel log output (truncated): WARNING: CPU: 1 PID: 5273 at net/core/dev.c:3535 skb_warn_bad_offload+0x81/0x140 ... Call Trace: <TASK> skb_checksum_help+0x12a/0x1f0 validate_xmit_skb+0x1a3/0x2d0 validate_xmit_skb_list+0x4f/0x80 sch_direct_xmit+0x1a2/0x380 __dev_xmit_skb+0x242/0x670 __dev_queue_xmit+0x3fc/0x7f0 ip6_finish_output2+0x25e/0x5d0 ip6_finish_output+0x1fc/0x3f0 ip6_tnl_xmit+0x608/0xc00 [ip6_tunnel] ip6gre_tunnel_xmit+0x1c0/0x390 [ip6_gre] dev_hard_start_xmit+0x63/0x1c0 __dev_queue_xmit+0x6d0/0x7f0 ip6_finish_output2+0x214/0x5d0 ip6_finish_output+0x1fc/0x3f0 ip6_xmit+0x2ca/0x6f0 ip6_finish_output+0x1fc/0x3f0 ip6_xmit+0x2ca/0x6f0 inet6_csk_xmit+0xeb/0x150 __tcp_transmit_skb+0x555/0xa80 tcp_write_xmit+0x32a/0xe90 tcp_sendmsg_locked+0x437/0x1110 tcp_sendmsg+0x2f/0x50 ... skb linear: 00000000: e4 3d 1a 7d ec 30 e4 3d 1a 7e 5d 90 86 dd 60 0e skb linear: 00000010: 00 0a 1b 34 3c 40 20 11 00 00 00 00 00 00 00 00 skb linear: 00000020: 00 00 00 00 00 12 20 11 00 00 00 00 00 00 00 00 skb linear: 00000030: 00 00 00 00 00 11 2f 00 04 01 04 01 01 00 00 00 skb linear: 00000040: 86 dd 60 0e 00 0a 1b 00 06 40 20 23 00 00 00 00 skb linear: 00000050: 00 00 00 00 00 00 00 00 00 12 20 23 00 00 00 00 skb linear: 00000060: 00 00 00 00 00 00 00 00 00 11 bf 96 14 51 13 f9 skb linear: 00000070: ae 27 a0 a8 2b e3 80 18 00 40 5b 6f 00 00 01 01 skb linear: 00000080: 08 0a 42 d4 50 d5 4b 70 f8 1a

Patch / fix

  • Linux Linux 4.20, 5.5, 5.11, 5.16, 6.1.149, 6.6.103, 6.12, 6.12.44, 6.16.4, 6.17
  • Siemens SIMATIC CN 4100 V5.0
  • linux Debian 12 6.1.153-1
  • linux Debian 13 6.12.48-1
  • linux Debian 14 6.16.5-1

debian advisories DEBIAN-CVE-2025-39770

  • linux Ubuntu 24.04 LTS 6.8.0-100.100
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1046.49
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1047.50
  • linux-gke Ubuntu 24.04 LTS 6.8.0-1043.48
  • linux-ibm Ubuntu 24.04 LTS 6.8.0-1044.44
  • linux-azure Ubuntu 24.04 LTS 6.8.0-1046.52
  • linux-gkeop Ubuntu 24.04 LTS 6.8.0-1030.33
  • linux-raspi Ubuntu 24.04 LTS 6.8.0-1047.51

ubuntu advisories UBUNTU-CVE-2025-39770

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel RHEL 10.0 6.12.0-55.33.1.el10_0
  • rv RHEL 10.0 6.12.0-55.33.1.el10_0
  • perf RHEL 10.0 6.12.0-55.33.1.el10_0
  • rtla RHEL 10.0 6.12.0-55.33.1.el10_0
  • libperf RHEL 10.0 6.12.0-55.33.1.el10_0
  • kernel-rt RHEL 10.0 6.12.0-55.33.1.el10_0
  • kernel-64k RHEL 10.0 6.12.0-55.33.1.el10_0
  • kernel-core RHEL 10.0 6.12.0-55.33.1.el10_0

red hat advisories RHSA-2025:15782

  • kernel-rt Linux Micro 6.2 6.12.0-160000.6.1
  • kernel-64kb SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.6.1
  • kernel-source SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.6.1
  • kernel-default SLES 16.0, SLE High Availability Extension 16.0, Linux Micro 6.2 +1 more 6.12.0-160000.6.1
  • kernel-default-base SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 6.12.0-160000.6.1.160000.2.4
  • kernel-syms SLES 16.0, Linux Micro Extras 6.2, SLES for SAP applications 16.0 6.12.0-160000.6.1
  • kernel-obs-qa SLES for SAP applications 16.0, SLES 16.0 6.12.0-160000.6.1
  • kernel-kvmsmall SLES for SAP applications 16.0, SLES 16.0 6.12.0-160000.6.1

suse advisories SUSE-SU-2025:21074-1SUSE-SU-2025:21139-1SUSE-SU-2026:20560-1SUSE-SU-2025:21179-1SUSE-SU-2025:20870-1SUSE-SU-2025:20898-1

  • kernel-rt openSUSE Leap 16.0 6.12.0-160000.6.1
  • dtb-aarch64 openSUSE Leap 16.0 6.12.0-160000.6.1
  • kernel-64kb openSUSE Leap 16.0 6.12.0-160000.6.1
  • kernel-syms openSUSE Leap 16.0 6.12.0-160000.6.1
  • kernel-obs-qa openSUSE Leap 16.0 6.12.0-160000.6.1
  • kernel-source openSUSE Leap 16.0 6.12.0-160000.6.1
  • kernel-default openSUSE Leap 16.0 6.12.0-160000.6.1
  • kernel-kvmsmall openSUSE Leap 16.0 6.12.0-160000.6.1

opensuse advisories openSUSE-SU-2025:20081-1

  • kernel-abi-stablelists AlmaLinux 10 6.12.0-55.33.1.el10_0

almalinux advisories ALSA-2025:15782

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2025-39770 updated cvss 5.7

kernel: net: gso: Forbid IPv6 TSO with extensions on devices with only IPV6_CSUM

  • Red Hat Enterprise Linux AppStream (v. 10) rv 6.12.0-55.33.1.el10_0, perf 6.12.0-55.33.1.el10_0, rtla 6.12.0-55.33.1.el10_0, python3-perf 6.12.0-55.33.1.el10_0, kernel-devel-matched 6.12.0-55.33.1.el10_0, kernel-64k-devel-matched 6.12.0-55.33.1.el10_0, +7 more Red Hat Enterprise Linux BaseOS (v. 10) kernel 6.12.0-55.33.1.el10_0, kernel-64k 6.12.0-55.33.1.el10_0, kernel-core 6.12.0-55.33.1.el10_0, kernel-tools 6.12.0-55.33.1.el10_0, kernel-modules 6.12.0-55.33.1.el10_0, kernel-64k-core 6.12.0-55.33.1.el10_0, +27 more Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) libperf 6.12.0-55.33.1.el10_0, kernel-debuginfo-common-s390x 6.12.0-55.33.1.el10_0, kernel-debuginfo-common-x86_64 6.12.0-55.33.1.el10_0, kernel-debuginfo-common-aarch64 6.12.0-55.33.1.el10_0, kernel-debuginfo-common-ppc64le 6.12.0-55.33.1.el10_0 Red Hat Enterprise Linux Real Time (v. 10) kernel-rt 6.12.0-55.33.1.el10_0, kernel-rt-64k 6.12.0-55.33.1.el10_0, kernel-rt-core 6.12.0-55.33.1.el10_0, kernel-rt-modules 6.12.0-55.33.1.el10_0, kernel-rt-64k-core 6.12.0-55.33.1.el10_0, kernel-rt-debug-core 6.12.0-55.33.1.el10_0, +14 more Red Hat Enterprise Linux Real Time for NFV (v. 10) kernel-rt 6.12.0-55.33.1.el10_0, kernel-rt-kvm 6.12.0-55.33.1.el10_0, kernel-rt-core 6.12.0-55.33.1.el10_0, kernel-rt-modules 6.12.0-55.33.1.el10_0, kernel-rt-debug-kvm 6.12.0-55.33.1.el10_0, kernel-rt-debug-core 6.12.0-55.33.1.el10_0, +6 more
    fixed: vendor fix RHSA-2025:15782
  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

cisa ICSA-26-295-11 updated cvss 7.5

Siemens SIMATIC S7-1500 CPU 1518(F)-4 PN/DP MFP

  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) >= 3.1.7 Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) >= 3.1.7 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) >= 3.1.7 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) >= 3.1.7 Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) >= 3.1.7
    affected: mitigation, no fix available

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

cisa ICSA-26-209-04 updated cvss 5.5

Siemens SIMATIC S7-1500 CPU 1518(F)-4 PN/DP MFP

  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) >= 3.1.6 Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) >= 3.1.6 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) >= 3.1.6 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) >= 3.1.6 Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) >= 3.1.6
    affected: mitigation, no fix available

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

cisa ICSA-25-162-05 updated cvss 5.5

Siemens SIMATIC S7-1500 CPU family

  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) >= 3.1.5 Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) >= 3.1.5 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) >= 3.1.5 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) >= 3.1.5 Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) >= 3.1.5
    affected: mitigation, no fix available

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

Exploit prediction

0.38% chance of exploitation in the next 30 days, higher than 31% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Linux Linux
  • Siemens SIMATIC CN 4100
  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP
  • Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP
  • Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP

Classification

Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.