CVE-2025-21926: linux kernel — Fix

Description

In the Linux kernel, the following vulnerability has been resolved: net: gso: fix ownership in __udp_gso_segment In __udp_gso_segment the skb destructor is removed before segmenting the skb but the socket reference is kept as-is. This is an issue if the original skb is later orphaned as we can hit the following bug: kernel BUG at ./include/linux/skbuff.h:3312! (skb_orphan) RIP: 0010:ip_rcv_core+0x8b2/0xca0 Call Trace: ip_rcv+0xab/0x6e0 __netif_receive_skb_one_core+0x168/0x1b0 process_backlog+0x384/0x1100 __napi_poll.constprop.0+0xa1/0x370 net_rx_action+0x925/0xe50 The above can happen following a sequence of events when using OpenVSwitch, when an OVS_ACTION_ATTR_USERSPACE action precedes an OVS_ACTION_ATTR_OUTPUT action: 1. OVS_ACTION_ATTR_USERSPACE is handled (in do_execute_actions): the skb goes through queue_gso_packets and then __udp_gso_segment, where its destructor is removed. 2. The segments' data are copied and sent to userspace. 3. OVS_ACTION_ATTR_OUTPUT is handled (in do_execute_actions) and the same original skb is sent to its path. 4. If it later hits skb_orphan, we hit the bug. Fix this by also removing the reference to the socket in __udp_gso_segment.

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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

Affected Products

Vendor	Product	Versions
linux	linux_kernel	4.18 — 5.4.291
linux	linux_kernel	5.5 — 5.10.235
linux	linux_kernel	5.11 — 5.15.179
linux	linux_kernel	5.16 — 6.1.131
linux	linux_kernel	6.2 — 6.6.83
linux	linux_kernel	6.7 — 6.12.19
linux	linux_kernel	6.13 — 6.13.7
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/01a83237644d6822bc7df2c5564fc81b0df84358 https://git.kernel.org/stable/c/084819b0d8b1bd433b90142371eb9450d657f8ca https://git.kernel.org/stable/c/455217ac9db0cf9349b3933664355e907bb1a569 https://git.kernel.org/stable/c/9f28205ddb76e86cac418332e952241d85fed0dc https://git.kernel.org/stable/c/a2d1cca955ed34873e524cc2e6e885450d262f05 https://git.kernel.org/stable/c/c32da44cc9298eaa6109e3fc2c2b4e07cc4bf11b https://git.kernel.org/stable/c/e8db70537878e1bb3fd83e5abcc6feefc0587828 https://git.kernel.org/stable/c/ee01b2f2d7d0010787c2343463965bbc283a497f

Other References

https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html

Frequently Asked Questions

What is CVE-2025-21926? +

In the Linux kernel, the following vulnerability has been resolved: net: gso: fix ownership in __udp_gso_segment In __udp_gso_segment the skb destructor is removed before segmenting the skb but the socket reference is kept as-is. This is an issue if the original skb is later orphaned as we can hit the following bug: kernel BUG at ./include/linux/skbuff.h:3312! (skb_orphan) RIP: 0010:ip_rcv_core+0x8b2/0xca0 Call Trace: ip_rcv+0xab/0x6e0 __netif_receive_skb_one_core+0x168/0x1b0 process_backlog+0x384/0x1100 __napi_poll.constprop.0+0xa1/0x370 net_rx_action+0x925/0xe50 The above can happen following a sequence of events when using OpenVSwitch, when an OVS_ACTION_ATTR_USERSPACE action precedes an OVS_ACTION_ATTR_OUTPUT action: 1. OVS_ACTION_ATTR_USERSPACE is handled (in do_execute_actions): the skb goes through queue_gso_packets and then __udp_gso_segment, where its destructor is removed. 2. The segments' data are copied and sent to userspace. 3. OVS_ACTION_ATTR_OUTPUT is handled (in do_execute_actions) and the same original skb is sent to its path. 4. If it later hits skb_orphan, we hit the bug. Fix this by also removing the reference to the socket in __udp_gso_segment. It has a CVSS v3.1 base score of 5.5 (MEDIUM).

How severe is CVE-2025-21926? +

CVE-2025-21926 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.

What products are affected by CVE-2025-21926? +

CVE-2025-21926 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-2025-21926? +

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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