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Unity Linux 20.1050e Security Update: kernel (UTSA-2026-102020)

high Nessus Plugin ID 338584

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-2026-102020 advisory.

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

 net: ipv6: fix NOREF dst use in seg6 and rpl lwtunnels

 seg6_input_core() and rpl_input() call ip6_route_input() which sets a NOREF dst on the skb, then pass it to dst_cache_set_ip6() invoking dst_hold() unconditionally.
 On PREEMPT_RT, ksoftirqd is preemptible and a higher-priority task can release the underlying pcpu_rt between the lookup and the caching through a concurrent FIB lookup on a shared nexthop.
 Simplified race sequence:

 ksoftirqd/X higher-prio task (same CPU X)
 ----------- -------------------------------- seg6_input_core(,skb)/rpl_input(skb) dst_cache_get()
 -> miss ip6_route_input(skb)
 -> ip6_pol_route(,skb,flags) [RT6_LOOKUP_F_DST_NOREF in flags]
 -> FIB lookup resolves fib6_nh [nhid=N route]
 -> rt6_make_pcpu_route() [creates pcpu_rt, refcount=1] pcpu_rt->sernum = fib6_sernum [fib6_sernum=W]
 -> cmpxchg(fib6_nh.rt6i_pcpu, NULL, pcpu_rt) [slot was empty, store succeeds]
 -> skb_dst_set_noref(skb, dst) [dst is pcpu_rt, refcount still 1]

 rt_genid_bump_ipv6()
 -> bumps fib6_sernum [fib6_sernum from W to Z] ip6_route_output()
 -> ip6_pol_route()
 -> FIB lookup resolves fib6_nh [nhid=N]
 -> rt6_get_pcpu_route() pcpu_rt->sernum != fib6_sernum [W <> Z, stale]
 -> prev = xchg(rt6i_pcpu, NULL)
 -> dst_release(prev) [prev is pcpu_rt, refcount 1->0, dead]

 dst = skb_dst(skb) [dst is the dead pcpu_rt] dst_cache_set_ip6(dst)
 -> dst_hold() on dead dst
 -> WARN / use-after-free

 For the race to occur, ksoftirqd must be preemptible (PREEMPT_RT without PREEMPT_RT_NEEDS_BH_LOCK) and a concurrent task must be able to release the pcpu_rt. Shared nexthop objects provide such a path, as two routes pointing to the same nhid share the same fib6_nh and its rt6i_pcpu entry.

 Fix seg6_input_core() and rpl_input() by calling skb_dst_force() after ip6_route_input() to force the NOREF dst into a refcounted one before caching.
 The output path is not affected as ip6_route_output() already returns a refcounted dst.

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

https://nvd.nist.gov/vuln/detail/CVE-2026-46099

http://www.nessus.org/u?7bd19d2e

http://www.nessus.org/u?d2f78dd2

Plugin Details

Severity: High

ID: 338584

File Name: unity_linux_UTSA-2026-102020.nasl

Version: 1.1

Type: Local

Published: 8/21/2026

Updated: 8/21/2026

Supported Sensors: Nessus

Risk Information

VPR

Risk Factor: Medium

Score: 4.5

Percentile: 57.6

CVSS v2

Risk Factor: High

Base Score: 7.6

Temporal Score: 5.6

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

CVSS Score Source: CVE-2026-46099

CVSS v3

Risk Factor: High

Base Score: 7.3

Temporal Score: 6.4

Vector: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:L/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: 8/17/2026

Vulnerability Publication Date: 5/27/2026

Reference Information

CVE: CVE-2026-46099