A newly found out native privilege escalation vulnerability dubbed ‘CIFSwitch’ within the Linux kernel may permit attackers to forge CIFS authentication key descriptions, abuse the kernel’s key request mechanism, and achieve root privileges.
The problem affects a couple of Linux distributions that send prone mixtures of the kernel CIFS and cifs-utils (variations 6.14 and better, even supposing some older variants also are affected).
CIFS (Not unusual Web Document Gadget) is a networking protocol that permits get admission to to recordsdata, folders, and gadgets throughout an area community. Linux makes use of it to mount, learn, and write knowledge from faraway techniques.
If a CIFS community proportion makes use of Kerberos for authentication, the Linux kernel asks a helper program in person area to accomplish authentication, with the cifs-utils choice of user-space equipment serving because the middleman.
“The kernel requests a cifs.spnego-type key, and the traditional keyutils/request-key config runs cifs.upcall as root to fetch or construct the Kerberos/SPNEGO subject material,” explains Asim Viladi Oglu Manizada, a SpaceX safety engineer who found out and named the CIFSwitch privilege escalation vulnerability in Linux.
The researcher says that the issue is composed of the Linux kernel’s CIFS subsystem failing to ensure that cifs.spnego key requests originate from the kernel’s CIFS shopper.
Consequently, an unprivileged person can create a cast cifs.spnego request and cause the traditional authentication workflow.
A cifs.spnego key request is utilized by the Linux keyring subsystem to procure authentication knowledge wanted through the CIFS/SMB shopper when connecting to a community proportion the use of Kerberos/SPNEGO authentication.
The flaw permits the root-privileged cifs.upcall helper to agree with attacker-controlled fields that it assumes have been generated through the kernel.
By way of abusing those fields to power a namespace swap after which triggering a Identify Carrier Transfer (NSS) search for prior to privileges are dropped, an area attacker can load a malicious NSS module and reach root code execution.
Manizada has printed an intensive technical document explaining the reason for the problem and the way it may be leveraged to reach root privileges.
Have an effect on, fixes, and the exploit
Manizada says that CIFSwitch used to be offered 19 years in the past, in 2007. He provides that it’s “non-universal” and exploiting it depends upon a number of elements, reminiscent of a prone kernel model.
Different necessities come with a prone cifs-utils model, the provision of person namespaces, and SELinux/AppArmor insurance policies that do not block the assault.
Some distributions Manizada confirms as prone with their default configurations are:
- Linux Mint 21.3 / 22.3
- CentOS Circulation 9
- Rocky Linux 9
- AlmaLinux 9
- Kali Linux 2021.4–2026.1
- SLES 15 SP7
The researcher famous that quite a lot of Ubuntu, Debian, Pop!_OS, openSUSE, Oracle Linux, and Amazon Linux variations may additionally be prone if ‘cifs-utils’ is put in.
Then again, there also are variations reminiscent of Ubuntu 26.04, Fedora 40-44, CentOS Circulation 10, Rocky Linux 10, SLES 16, AlmaLinux 10, and openSUSE Soar 16, the place the default SELinux/AppArmor settings save you exploitation of CIFSwitch.
Additionally, Amazon Linux 2 and Kali Linux 2019.4 and 2020.4 don’t seem to be affected in any respect, as their cifs-utils variations lack the namespace-switch capability.
CIFSwitch has been mounted through a kernel patch that provides validation of cifs.spnego request origins (upstream devote 3da1fdf), however the precise kernel variations that send that patch range in line with distribution.
The researcher recommends that customers disable or blacklist the CIFS module if unused, take away the cifs-utils bundle if useless, and disable unprivileged person namespaces.
Manizada printed a proof-of-concept (PoC) exploit for CIFSwitch, which will assist organizations validate the effectiveness of the implemented patches and mitigations.
CIFSwitch is the newest in a sequence of privilege-elevation flaws impacting Linux techniques that have been just lately disclosed, together with ‘Replica Fail,’ ‘Grimy Frag,’ ‘Fragnesia,’ ‘DirtyDecrypt,’ and ‘PinTheft.’
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