CVE-2024-43882

CVE Details

Release Date:

2024-08-21

Description

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.

See more information about CVE-2024-43882 from MITRE CVE dictionary and NIST NVD

CVSS Scoring

NOTE: The following CVSS v3.1 metrics and score provided are preliminary and subject to review.

Base Score:	7	CVSS Vector:	CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
Attack Vector:	Local network	Attack Complexity:	High
Privileges Required:	Low	User Interaction:	None
Scope:	Unchanged	Confidentiality Impact:	High
Integrity Impact:	High	Availability Impact:	High

Errata information

Platform	Errata	Release Date
Oracle Linux version 7 (kernel-uek)	ELSA-2024-12780	2024-10-11
Oracle Linux version 7 (kernel-uek)	ELSA-2024-12782	2024-10-14
Oracle Linux version 8 (kernel-uek)	ELSA-2024-12780	2024-10-11
Oracle Linux version 8 (kernel-uek)	ELSA-2024-12782	2024-10-14
Oracle Linux version 8 (kernel-uek)	ELSA-2024-12815	2024-11-11
Oracle Linux version 9 (kernel-uek)	ELSA-2024-12815	2024-11-11