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Unity Linux 20.1050e Security Update: kernel (UTSA-2026-007263)
medium Nessus Plugin ID 306981
Synopsis
The Unity Linux host is missing one or more security updates.Description
The Unity Linux 20 host has a package installed that is affected by a vulnerability as referenced in the UTSA-2026-007263 advisory.In the Linux kernel, the following vulnerability has been resolved:
inet: inet_defrag: prevent sk release while still in use
ip_local_out() and other functions can pass skb->sk as function argument.
If the skb is a fragment and reassembly happens before such function call returns, the sk must not be released.
This affects skb fragments reassembled via netfilter or similar modules, e.g. openvswitch or ct_act.c, when run as part of tx pipeline.
Eric Dumazet made an initial analysis of this bug. Quoting Eric:
Calling ip_defrag() in output path is also implying skb_orphan(), which is buggy because output path relies on sk not disappearing.
A relevant old patch about the issue was :
8282f27449bf (inet: frag: Always orphan skbs inside ip_defrag())
[..]
net/ipv4/ip_output.c depends on skb->sk being set, and probably to an inet socket, not an arbitrary one.
If we orphan the packet in ipvlan, then downstream things like FQ packet scheduler will not work properly.
We need to change ip_defrag() to only use skb_orphan() when really needed, ie whenever frag_list is going to be used.
Eric suggested to stash sk in fragment queue and made an initial patch.
However there is a problem with this:
If skb is refragmented again right after, ip_do_fragment() will copy head->sk to the new fragments, and sets up destructor to sock_wfree.
IOW, we have no choice but to fix up sk_wmem accouting to reflect the fully reassembled skb, else wmem will underflow.
This change moves the orphan down into the core, to last possible moment.
As ip_defrag_offset is aliased with sk_buff->sk member, we must move the offset into the FRAG_CB, else skb->sk gets clobbered.
This allows to delay the orphaning long enough to learn if the skb has to be queued or if the skb is completing the reasm queue.
In the former case, things work as before, skb is orphaned. This is safe because skb gets queued/stolen and won't continue past reasm engine.
In the latter case, we will steal the skb->sk reference, reattach it to the head skb, and fix up wmem accouting when inet_frag inflates truesize.
Tenable has extracted the preceding description block directly from the Unity Linux security advisory.
Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.
Solution
Update the affected kernel package.See Also
http://www.nessus.org/u?4bbd6f99
Plugin Details
Severity: Medium
ID: 306981
File Name: unity_linux_UTSA-2026-007263.nasl
Version: 1.1
Type: Local
Published: 4/17/2026
Updated: 4/17/2026
Supported Sensors: Nessus
Risk Information
VPR
Risk Factor: Medium
Score: 4.4
CVSS v2
Risk Factor: Medium
Base Score: 4.6
Temporal Score: 3.4
Vector: CVSS2#AV:L/AC:L/Au:S/C:N/I:N/A:C
CVSS Score Source: CVE-2024-26921
CVSS v3
Risk Factor: Medium
Base Score: 5.5
Temporal Score: 4.8
Vector: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C
Vulnerability Information
Required KB Items: Host/local_checks_enabled, Host/cpu, Host/UOS-Server/release, Host/UOS-Server/rpm-list
Exploit Ease: No known exploits are available
Patch Publication Date: 4/17/2026
Vulnerability Publication Date: 4/18/2024
Reference Information
CVE: CVE-2024-26921