CVE-2025-39770 (GCVE-0-2025-39770)
Vulnerability from cvelistv5 – Published: 2025-09-11 16:56 – Updated: 2026-09-08 08:42
VLAI
EPSS
VEX
Title
net: gso: Forbid IPv6 TSO with extensions on devices with only IPV6_CSUM
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
Severity
7.5 (High)
Assigner
References
9 references
Impacted products
9 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Linux | Linux |
Affected:
a84978a9cda68f0afe3f01d476c68db21526baf1 , < a0478d7e888028f85fa7785ea838ce0ca09398e2
(git)
Affected: c69bc67c1cb211aa390bea6e512bb01b1241fefb , < 2156d9e9f2e483c8c3906c0ea57ea312c1424235 (git) Affected: 04c20a9356f283da623903e81e7c6d5df7e4dc3c , < 041e2f945f82fdbd6fff577b79c33469430297aa (git) Affected: 04c20a9356f283da623903e81e7c6d5df7e4dc3c , < 794ddbb7b63b6828c75967b9bcd43b086716e7a1 (git) Affected: 04c20a9356f283da623903e81e7c6d5df7e4dc3c , < 864e3396976ef41de6cc7bc366276bf4e084fff2 (git) Affected: bcefc3cd7f592a70fcbbbfd7ad1fbc69172ea78b (git) Affected: 477b35d94a21530046fe91589960732fcf2b29ed (git) Affected: a27a5c40ee4cbe00294e2c76160de5f2589061ba (git) Affected: 9f605135a5c0fe614c2b15197b9ced1e217eca59 (git) Affected: 705350fbd6ed4b5d89ee045fa57a0594a72b17d7 (git) Affected: 6.1.116 , < 6.1.149 (semver) Affected: 6.6.60 , < 6.6.103 (semver) Affected: 4.19.323 , < 4.20 (semver) Affected: 5.4.285 , < 5.5 (semver) Affected: 5.10.229 , < 5.11 (semver) Affected: 5.15.171 , < 5.16 (semver) Affected: 6.11.7 , < 6.12 (semver) |
guessed | |
| Linux | Linux |
Affected:
6.12
Unaffected: 0 , < 6.12 (semver) Unaffected: 6.1.149 , ≤ 6.1.* (semver) Unaffected: 6.6.103 , ≤ 6.6.* (semver) Unaffected: 6.12.44 , ≤ 6.12.* (semver) Unaffected: 6.16.4 , ≤ 6.16.* (semver) Unaffected: 6.17 , ≤ * (original_commit_for_fix) |
guessed | |
| Siemens | SIMATIC CN 4100 |
Affected:
0 , < V5.0
(custom)
|
guessed | |
| Siemens | SIMATIC S7-1500 CPU 1518-4 PN/DP MFP |
Affected:
V3.1.5 , < *
(custom)
|
guessed | |
| Siemens | SIMATIC S7-1500 CPU 1518-4 PN/DP MFP |
Affected:
V3.1.6 , < *
(custom)
|
guessed | |
| Siemens | SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP |
Affected:
V3.1.5 , < *
(custom)
|
guessed | |
| Siemens | SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP |
Affected:
V3.1.6 , < *
(custom)
|
guessed | |
| Siemens | SIPLUS S7-1500 CPU 1518-4 PN/DP MFP |
Affected:
V3.1.5 , < *
(custom)
|
guessed | |
| Siemens | SIPLUS S7-1500 CPU 1518-4 PN/DP MFP |
Affected:
V3.1.6 , < *
(custom)
|
guessed |
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"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: gso: Forbid IPv6 TSO with extensions on devices with only IPV6_CSUM\n\nWhen performing Generic Segmentation Offload (GSO) on an IPv6 packet that\ncontains extension headers, the kernel incorrectly requests checksum offload\nif the egress device only advertises NETIF_F_IPV6_CSUM feature, which has\na strict contract: it supports checksum offload only for plain TCP or UDP\nover IPv6 and explicitly does not support packets with extension headers.\nThe current GSO logic violates this contract by failing to disable the feature\nfor packets with extension headers, such as those used in GREoIPv6 tunnels.\n\nThis violation results in the device being asked to perform an operation\nit cannot support, leading to a `skb_warn_bad_offload` warning and a collapse\nof network throughput. While device TSO/USO is correctly bypassed in favor\nof software GSO for these packets, the GSO stack must be explicitly told not\nto request checksum offload.\n\nMask NETIF_F_IPV6_CSUM, NETIF_F_TSO6 and NETIF_F_GSO_UDP_L4\nin gso_features_check if the IPv6 header contains extension headers to compute\nchecksum in software.\n\nThe exception is a BIG TCP extension, which, as stated in commit\n68e068cabd2c6c53 (\"net: reenable NETIF_F_IPV6_CSUM offload for BIG TCP packets\"):\n\"The feature is only enabled on devices that support BIG TCP TSO.\nThe header is only present for PF_PACKET taps like tcpdump,\nand not transmitted by physical devices.\"\n\nkernel log output (truncated):\nWARNING: CPU: 1 PID: 5273 at net/core/dev.c:3535 skb_warn_bad_offload+0x81/0x140\n...\nCall Trace:\n \u003cTASK\u003e\n skb_checksum_help+0x12a/0x1f0\n validate_xmit_skb+0x1a3/0x2d0\n validate_xmit_skb_list+0x4f/0x80\n sch_direct_xmit+0x1a2/0x380\n __dev_xmit_skb+0x242/0x670\n __dev_queue_xmit+0x3fc/0x7f0\n ip6_finish_output2+0x25e/0x5d0\n ip6_finish_output+0x1fc/0x3f0\n ip6_tnl_xmit+0x608/0xc00 [ip6_tunnel]\n ip6gre_tunnel_xmit+0x1c0/0x390 [ip6_gre]\n dev_hard_start_xmit+0x63/0x1c0\n __dev_queue_xmit+0x6d0/0x7f0\n ip6_finish_output2+0x214/0x5d0\n ip6_finish_output+0x1fc/0x3f0\n ip6_xmit+0x2ca/0x6f0\n ip6_finish_output+0x1fc/0x3f0\n ip6_xmit+0x2ca/0x6f0\n inet6_csk_xmit+0xeb/0x150\n __tcp_transmit_skb+0x555/0xa80\n tcp_write_xmit+0x32a/0xe90\n tcp_sendmsg_locked+0x437/0x1110\n tcp_sendmsg+0x2f/0x50\n...\nskb linear: 00000000: e4 3d 1a 7d ec 30 e4 3d 1a 7e 5d 90 86 dd 60 0e\nskb linear: 00000010: 00 0a 1b 34 3c 40 20 11 00 00 00 00 00 00 00 00\nskb linear: 00000020: 00 00 00 00 00 12 20 11 00 00 00 00 00 00 00 00\nskb linear: 00000030: 00 00 00 00 00 11 2f 00 04 01 04 01 01 00 00 00\nskb linear: 00000040: 86 dd 60 0e 00 0a 1b 00 06 40 20 23 00 00 00 00\nskb linear: 00000050: 00 00 00 00 00 00 00 00 00 12 20 23 00 00 00 00\nskb linear: 00000060: 00 00 00 00 00 00 00 00 00 11 bf 96 14 51 13 f9\nskb linear: 00000070: ae 27 a0 a8 2b e3 80 18 00 40 5b 6f 00 00 01 01\nskb linear: 00000080: 08 0a 42 d4 50 d5 4b 70 f8 1a"
}
],
"metrics": [
{
"cvssV3_1": {
"baseScore": 7.5,
"baseSeverity": "HIGH",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"version": "3.1"
},
"scenarios": [
{
"lang": "en",
"value": "AV:N - The defect is in the generic packet-transmit path (`net/core/dev.c`), and the reproducer is a remote TCP peer whose connection to a service egressing over an ip6gre/ip6ip6 tunnel makes the kernel build a GSO skb carrying the default encap-limit destination-options header, dropping every reply and emitting a WARN. No local access is needed to drive the trigger.\nAC:L - The failure is fully deterministic \u2014 there is no race, timing window, or memory-layout dependency; `skb_csum_hwoffload_help()` unconditionally routes any GSO IPv6 skb with an extension header into `skb_checksum_help()`, which warns and drops on every single packet. The NIC feature set (`IPV6_CSUM` + `TSO6`, no `HW_CSUM`) is the common case across dozens of mainstream drivers.\nPR:N - The remote client needs no credentials \u2014 merely establishing a connection and pulling more than one MSS of data from a service behind an IPv6 tunnel is sufficient. Locally the bar is likewise nil: `ipv6_set_opt_hdr()` at `net/ipv6/ipv6_sockglue.c:312` exempts `IPV6_RTHDR` from its `CAP_NET_RAW` check, so any unprivileged process can attach an SRH to a TCPv6 socket and hit the same path.\nUI:N - The attacker\u0027s own traffic drives the transmit path directly; no administrator or victim needs to open a file, mount anything, or take any action.\nS:U - The WARN, the packet drop, and any resulting panic all occur inside the kernel\u0027s own security authority on the same host, crossing no VM, IOMMU, container, or sandbox boundary.\nC:N - The skb is discarded via `kfree_skb()` with no out-of-bounds access and no kernel memory read primitive; the attacker learns nothing, as `skb_dump()` output goes only to the target\u0027s ring buffer, which they cannot read.\nI:N - No data is modified \u2014 the packet is rejected before reaching the device rather than being transmitted with a bad checksum, and there is no out-of-bounds or freed-memory write anywhere on the path.\nA:H - `skb_warn_bad_offload()` fires a `WARN(1)` that taints the kernel and becomes a full panic under `panic_on_warn`, and `validate_xmit_skb()` then destroys the skb, so every qualifying packet is silently discarded \u2014 a total collapse of throughput and loss of connectivity for the affected tunnel or interface, sustained for as long as the attacker keeps sending."
}
]
}
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: gso: Forbid IPv6 TSO with extensions on devices with only IPV6_CSUM\n\nWhen performing Generic Segmentation Offload (GSO) on an IPv6 packet that\ncontains extension headers, the kernel incorrectly requests checksum offload\nif the egress device only advertises NETIF_F_IPV6_CSUM feature, which has\na strict contract: it supports checksum offload only for plain TCP or UDP\nover IPv6 and explicitly does not support packets with extension headers.\nThe current GSO logic violates this contract by failing to disable the feature\nfor packets with extension headers, such as those used in GREoIPv6 tunnels.\n\nThis violation results in the device being asked to perform an operation\nit cannot support, leading to a `skb_warn_bad_offload` warning and a collapse\nof network throughput. While device TSO/USO is correctly bypassed in favor\nof software GSO for these packets, the GSO stack must be explicitly told not\nto request checksum offload.\n\nMask NETIF_F_IPV6_CSUM, NETIF_F_TSO6 and NETIF_F_GSO_UDP_L4\nin gso_features_check if the IPv6 header contains extension headers to compute\nchecksum in software.\n\nThe exception is a BIG TCP extension, which, as stated in commit\n68e068cabd2c6c53 (\"net: reenable NETIF_F_IPV6_CSUM offload for BIG TCP packets\"):\n\"The feature is only enabled on devices that support BIG TCP TSO.\nThe header is only present for PF_PACKET taps like tcpdump,\nand not transmitted by physical devices.\"\n\nkernel log output (truncated):\nWARNING: CPU: 1 PID: 5273 at net/core/dev.c:3535 skb_warn_bad_offload+0x81/0x140\n...\nCall Trace:\n \u003cTASK\u003e\n skb_checksum_help+0x12a/0x1f0\n validate_xmit_skb+0x1a3/0x2d0\n validate_xmit_skb_list+0x4f/0x80\n sch_direct_xmit+0x1a2/0x380\n __dev_xmit_skb+0x242/0x670\n __dev_queue_xmit+0x3fc/0x7f0\n ip6_finish_output2+0x25e/0x5d0\n ip6_finish_output+0x1fc/0x3f0\n ip6_tnl_xmit+0x608/0xc00 [ip6_tunnel]\n ip6gre_tunnel_xmit+0x1c0/0x390 [ip6_gre]\n dev_hard_start_xmit+0x63/0x1c0\n __dev_queue_xmit+0x6d0/0x7f0\n ip6_finish_output2+0x214/0x5d0\n ip6_finish_output+0x1fc/0x3f0\n ip6_xmit+0x2ca/0x6f0\n ip6_finish_output+0x1fc/0x3f0\n ip6_xmit+0x2ca/0x6f0\n inet6_csk_xmit+0xeb/0x150\n __tcp_transmit_skb+0x555/0xa80\n tcp_write_xmit+0x32a/0xe90\n tcp_sendmsg_locked+0x437/0x1110\n tcp_sendmsg+0x2f/0x50\n...\nskb linear: 00000000: e4 3d 1a 7d ec 30 e4 3d 1a 7e 5d 90 86 dd 60 0e\nskb linear: 00000010: 00 0a 1b 34 3c 40 20 11 00 00 00 00 00 00 00 00\nskb linear: 00000020: 00 00 00 00 00 12 20 11 00 00 00 00 00 00 00 00\nskb linear: 00000030: 00 00 00 00 00 11 2f 00 04 01 04 01 01 00 00 00\nskb linear: 00000040: 86 dd 60 0e 00 0a 1b 00 06 40 20 23 00 00 00 00\nskb linear: 00000050: 00 00 00 00 00 00 00 00 00 12 20 23 00 00 00 00\nskb linear: 00000060: 00 00 00 00 00 00 00 00 00 11 bf 96 14 51 13 f9\nskb linear: 00000070: ae 27 a0 a8 2b e3 80 18 00 40 5b 6f 00 00 01 01\nskb linear: 00000080: 08 0a 42 d4 50 d5 4b 70 f8 1a"
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"source": "SUSE CSAF VEX",
"status": "interim",
"title": "SUSE CVE CVE-2025-39770",
"url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2025-39770.json",
"version": "48"
}
}
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.
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