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Unity Linux 20.1070a Security Update: kernel (UTSA-2025-401373)
high Nessus Plugin ID 266993
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-2025-401373 advisory.In the Linux kernel, the following vulnerability has been resolved:
sched: sch_cake: fix bulk flow accounting logic for host fairness
In sch_cake, we keep track of the count of active bulk flows per host, when running in dst/src host fairness mode, which is used as the round-robin weight when iterating through flows. The count of active bulk flows is updated whenever a flow changes state.
This has a peculiar interaction with the hash collision handling: when a hash collision occurs (after the set-associative hashing), the state of the hash bucket is simply updated to match the new packet that collided, and if host fairness is enabled, that also means assigning new per-host state to the flow. For this reason, the bulk flow counters of the host(s) assigned to the flow are decremented, before new state is assigned (and the counters, which may not belong to the same host anymore, are incremented again).
Back when this code was introduced, the host fairness mode was always enabled, so the decrement was unconditional. When the configuration flags were introduced the *increment* was made conditional, but the *decrement* was not. Which of course can lead to a spurious decrement (and associated wrap-around to U16_MAX).
AFAICT, when host fairness is disabled, the decrement and wrap-around happens as soon as a hash collision occurs (which is not that common in itself, due to the set-associative hashing). However, in most cases this is harmless, as the value is only used when host fairness mode is enabled. So in order to trigger an array overflow, sch_cake has to first be configured with host fairness disabled, and while running in this mode, a hash collision has to occur to cause the overflow. Then, the qdisc has to be reconfigured to enable host fairness, which leads to the array out-of-bounds because the wrapped-around value is retained and used as an array index. It seems that syzbot managed to trigger this, which is quite impressive in its own right.
This patch fixes the issue by introducing the same conditional check on decrement as is used on increment.
The original bug predates the upstreaming of cake, but the commit listed in the Fixes tag touched that code, meaning that this patch won't apply before that.
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
Plugin Details
Severity: High
ID: 266993
File Name: unity_linux_UTSA-2025-401373.nasl
Version: 1.2
Type: local
Published: 10/7/2025
Updated: 10/15/2025
Supported Sensors: Nessus
Risk Information
VPR
Risk Factor: Medium
Score: 6.0
CVSS v2
Risk Factor: Medium
Base Score: 6.2
Temporal Score: 4.6
Vector: CVSS2#AV:L/AC:L/Au:S/C:C/I:N/A:C
CVSS Score Source: CVE-2024-46828
CVSS v3
Risk Factor: High
Base Score: 7.1
Temporal Score: 6.2
Vector: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/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: 7/8/2025
Vulnerability Publication Date: 9/27/2024
Reference Information
CVE: CVE-2024-46828