CVE-2026-31517

Description

In the Linux kernel, the following vulnerability has been resolved: xfrm: iptfs: fix skb_put() panic on non-linear skb during reassembly In iptfs_reassem_cont(), IP-TFS attempts to append data to the new inner packet 'newskb' that is being reassembled. First a zero-copy approach is tried if it succeeds then newskb becomes non-linear. When a subsequent fragment in the same datagram does not meet the fast-path conditions, a memory copy is performed. It calls skb_put() to append the data and as newskb is non-linear it triggers SKB_LINEAR_ASSERT check. Oops: invalid opcode: 0000 [#1] SMP NOPTI [...] RIP: 0010:skb_put+0x3c/0x40 [...] Call Trace: <IRQ> iptfs_reassem_cont+0x1ab/0x5e0 [xfrm_iptfs] iptfs_input_ordered+0x2af/0x380 [xfrm_iptfs] iptfs_input+0x122/0x3e0 [xfrm_iptfs] xfrm_input+0x91e/0x1a50 xfrm4_esp_rcv+0x3a/0x110 ip_protocol_deliver_rcu+0x1d7/0x1f0 ip_local_deliver_finish+0xbe/0x1e0 __netif_receive_skb_core.constprop.0+0xb56/0x1120 __netif_receive_skb_list_core+0x133/0x2b0 netif_receive_skb_list_internal+0x1ff/0x3f0 napi_complete_done+0x81/0x220 virtnet_poll+0x9d6/0x116e [virtio_net] __napi_poll.constprop.0+0x2b/0x270 net_rx_action+0x162/0x360 handle_softirqs+0xdc/0x510 __irq_exit_rcu+0xe7/0x110 irq_exit_rcu+0xe/0x20 common_interrupt+0x85/0xa0 </IRQ> <TASK> Fix this by checking if the skb is non-linear. If it is, linearize it by calling skb_linearize(). As the initial allocation of newskb originally reserved enough tailroom for the entire reassembled packet we do not need to check if we have enough tailroom or extend it.

CVSS v3.1 Score

5.5

MEDIUM

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS — Exploit Prediction

0.0001

Probability of exploitation

0.02%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-401 CWE-401

Affected Products

Vendor	Product	Versions
linux	linux_kernel	6.14.1 — 6.18.21
linux	linux_kernel	6.19 — 6.19.11
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All

References

Advisories & Patches

https://git.kernel.org/stable/c/0b352f83cabfefdaafa806d6471f0eca117dc7d5 https://git.kernel.org/stable/c/33a7b36268933c75bdc355e5531951e0ea9f1951 https://git.kernel.org/stable/c/7fdfe8f6efeb0e1200e22a903f2471539f54522b

Frequently Asked Questions

What is CVE-2026-31517? +

In the Linux kernel, the following vulnerability has been resolved: xfrm: iptfs: fix skb_put() panic on non-linear skb during reassembly In iptfs_reassem_cont(), IP-TFS attempts to append data to the new inner packet 'newskb' that is being reassembled. First a zero-copy approach is tried if it succeeds then newskb becomes non-linear. When a subsequent fragment in the same datagram does not meet the fast-path conditions, a memory copy is performed. It calls skb_put() to append the data and as newskb is non-linear it triggers SKB_LINEAR_ASSERT check. Oops: invalid opcode: 0000 [#1] SMP NOPTI [...] RIP: 0010:skb_put+0x3c/0x40 [...] Call Trace: <IRQ> iptfs_reassem_cont+0x1ab/0x5e0 [xfrm_iptfs] iptfs_input_ordered+0x2af/0x380 [xfrm_iptfs] iptfs_input+0x122/0x3e0 [xfrm_iptfs] xfrm_input+0x91e/0x1a50 xfrm4_esp_rcv+0x3a/0x110 ip_protocol_deliver_rcu+0x1d7/0x1f0 ip_local_deliver_finish+0xbe/0x1e0 __netif_receive_skb_core.constprop.0+0xb56/0x1120 __netif_receive_skb_list_core+0x133/0x2b0 netif_receive_skb_list_internal+0x1ff/0x3f0 napi_complete_done+0x81/0x220 virtnet_poll+0x9d6/0x116e [virtio_net] __napi_poll.constprop.0+0x2b/0x270 net_rx_action+0x162/0x360 handle_softirqs+0xdc/0x510 __irq_exit_rcu+0xe7/0x110 irq_exit_rcu+0xe/0x20 common_interrupt+0x85/0xa0 </IRQ> <TASK> Fix this by checking if the skb is non-linear. If it is, linearize it by calling skb_linearize(). As the initial allocation of newskb originally reserved enough tailroom for the entire reassembled packet we do not need to check if we have enough tailroom or extend it. It has a CVSS v3.1 base score of 5.5 (MEDIUM).

How severe is CVE-2026-31517? +

CVE-2026-31517 has a CVSS v3.1 score of 5.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0001, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-31517? +

CVE-2026-31517 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-31517? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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