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Unity Linux 20.1050e Security Update: kernel (UTSA-2026-005185)

high Nessus Plugin ID 296938

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-2026-005185 advisory.

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

 pfifo_tail_enqueue: Drop new packet when sch->limit == 0

 Expected behaviour:
 In case we reach scheduler's limit, pfifo_tail_enqueue() will drop a packet in scheduler's queue and decrease scheduler's qlen by one.
 Then, pfifo_tail_enqueue() enqueue new packet and increase scheduler's qlen by one. Finally, pfifo_tail_enqueue() return `NET_XMIT_CN` status code.

 Weird behaviour:
 In case we set `sch->limit == 0` and trigger pfifo_tail_enqueue() on a scheduler that has no packet, the 'drop a packet' step will do nothing.
 This means the scheduler's qlen still has value equal 0.
 Then, we continue to enqueue new packet and increase scheduler's qlen by one. In summary, we can leverage pfifo_tail_enqueue() to increase qlen by one and return `NET_XMIT_CN` status code.

 The problem is:
 Let's say we have two qdiscs: Qdisc_A and Qdisc_B.
 - Qdisc_A's type must have '->graft()' function to create parent/child relationship.
 Let's say Qdisc_A's type is `hfsc`. Enqueue packet to this qdisc will trigger `hfsc_enqueue`.
 - Qdisc_B's type is pfifo_head_drop. Enqueue packet to this qdisc will trigger `pfifo_tail_enqueue`.
 - Qdisc_B is configured to have `sch->limit == 0`.
 - Qdisc_A is configured to route the enqueued's packet to Qdisc_B.

 Enqueue packet through Qdisc_A will lead to:
 - hfsc_enqueue(Qdisc_A) -> pfifo_tail_enqueue(Qdisc_B)
 - Qdisc_B->q.qlen += 1
 - pfifo_tail_enqueue() return `NET_XMIT_CN`
 - hfsc_enqueue() check for `NET_XMIT_SUCCESS` and see `NET_XMIT_CN` => hfsc_enqueue() don't increase qlen of Qdisc_A.

 The whole process lead to a situation where Qdisc_A->q.qlen == 0 and Qdisc_B->q.qlen == 1.
 Replace 'hfsc' with other type (for example: 'drr') still lead to the same problem.
 This violate the design where parent's qlen should equal to the sum of its childrens'qlen.

 Bug impact: This issue can be used for user->kernel privilege escalation when it is reachable.

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?3bfb8ef8

http://www.nessus.org/u?d8147ebf

https://nvd.nist.gov/vuln/detail/CVE-2025-21702

Plugin Details

Severity: High

ID: 296938

File Name: unity_linux_UTSA-2026-005185.nasl

Version: 1.1

Type: local

Published: 1/27/2026

Updated: 1/27/2026

Supported Sensors: Nessus

Risk Information

VPR

Risk Factor: High

Score: 7.4

CVSS v2

Risk Factor: Medium

Base Score: 6

Temporal Score: 4.4

Vector: CVSS2#AV:L/AC:H/Au:S/C:C/I:C/A:C

CVSS Score Source: CVE-2025-21702

CVSS v3

Risk Factor: High

Base Score: 7

Temporal Score: 6.1

Vector: CVSS:3.0/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/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: 1/28/2026

Vulnerability Publication Date: 2/18/2025

Reference Information

CVE: CVE-2025-21702