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Unity Linux 20.1070a Security Update: kernel (UTSA-2025-990367)
high Nessus Plugin ID 272642
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-2025-990367 advisory.In the Linux kernel, the following vulnerability has been resolved:
exec: Fix ToCToU between perm check and set-uid/gid usage
When opening a file for exec via do_filp_open(), permission checking is done against the file's metadata at that moment, and on success, a file pointer is passed back. Much later in the execve() code path, the file metadata (specifically mode, uid, and gid) is used to determine if/how to set the uid and gid. However, those values may have changed since the permissions check, meaning the execution may gain unintended privileges.
For example, if a file could change permissions from executable and not set-id:
---------x 1 root root 16048 Aug 7 13:16 target
to set-id and non-executable:
---S------ 1 root root 16048 Aug 7 13:16 target
it is possible to gain root privileges when execution should have been disallowed.
While this race condition is rare in real-world scenarios, it has been observed (and proven exploitable) when package managers are updating the setuid bits of installed programs. Such files start with being world-executable but then are adjusted to be group-exec with a set-uid bit. For example, chmod o-x,u+s target makes target executable only by uid root and gid cdrom, while also becoming setuid-root:
-rwxr-xr-x 1 root cdrom 16048 Aug 7 13:16 target
becomes:
-rwsr-xr-- 1 root cdrom 16048 Aug 7 13:16 target
But racing the chmod means users without group cdrom membership can get the permission to execute target just before the chmod, and when the chmod finishes, the exec reaches brpm_fill_uid(), and performs the setuid to root, violating the expressed authorization of only cdrom group members can setuid to root.
Re-check that we still have execute permissions in case the metadata has changed. It would be better to keep a copy from the perm-check time, but until we can do that refactoring, the least-bad option is to do a full inode_permission() call (under inode lock). It is understood that this is safe against dead-locks, but hardly optimal.
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: 272642
File Name: unity_linux_UTSA-2025-990367.nasl
Version: 1.1
Type: local
Published: 11/5/2025
Updated: 11/5/2025
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-2024-43882
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: 11/5/2025
Vulnerability Publication Date: 4/9/2024
Reference Information
CVE: CVE-2024-43882