CVE-2026-46243: linux linux kernel (public PoC)

What it is

In the Linux kernel, the following vulnerability has been resolved: smb: client: reject userspace cifs.spnego descriptions cifs.spnego key descriptions contain authority-bearing fields such as pid, uid, creduid, and upcall_target that cifs.upcall treats as kernel-originating inputs. However, userspace can also create keys of this type through request_key(2) or add_key(2), allowing those fields to be supplied without CIFS origin. Only accept cifs.spnego descriptions while CIFS is using its private spnego_cred to request the key.

Weakness	CWE-20 CWE-825
CVSS vector	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N (source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67)
ATT&CK tactics	Initial Access

Exploitation evidence

First exploit evidence seen: 2026-06-01 (earliest date across the sources below).

Exploited in the wild

No source on this site lists in-the-wild exploitation yet (CISA KEV, VulnCheck KEV).

Public exploit code

GitHub proof-of-concept repositories

5 public repositories from 5 accounts, first seen 2026-06-01. Most starred: MrForkBomb/CIFSwitch-Checker-CVE-2026-46243 (2 stars), view repository.

Verify before running: public PoCs can be malicious. Read the code and only run it in an isolated lab. A PoC means exploit code is public, not that this CVE is exploited in the wild.

Sources: nomi-sec/PoC-in-GitHub.

How to fix it

Fixed versions

linux linux kernel: upgrade to 5.10.258 or later (affected from 2.6.24.1)
linux linux kernel: upgrade to 5.15.209 or later (affected from 5.11)
linux linux kernel: upgrade to 6.1.175 or later (affected from 5.16)
linux linux kernel: upgrade to 6.6.142 or later (affected from 6.2)
linux linux kernel: upgrade to 6.12.92 or later (affected from 6.7)
linux linux kernel: upgrade to 6.18.34 or later (affected from 6.13)
linux linux kernel: upgrade to 7.0.11 or later (affected from 6.19)

Derived from the NVD CPE configuration (versionEndExcluding / versionEndIncluding). Always confirm with the vendor advisory.

Vendor advisories and patches

MITRE ATT&CK mitigations for this chain

M1048 Application Isolation and Sandboxing (for T1190) : Application isolation will limit what other processes and system features the exploited target can access.
M1037 Filter Network Traffic (for T1190) : Restrict outbound network traffic from public-facing servers to prevent unauthorized connections from initiating communications with attacker-controlled infrastructure. While this may not prevent the initial exploitation, it limits the attacker's ability to verify and control the compromised server post-exploit, reduci
M1030 Network Segmentation (for T1190) : Segment externally facing servers and services from the rest of the network with a DMZ or on separate hosting infrastructure.
M1016 Vulnerability Scanning (for T1190) : Regularly scan externally facing systems for vulnerabilities and establish procedures to rapidly patch systems when critical vulnerabilities are discovered through scanning and through public disclosure.
M1026 Privileged Account Management (for T1190) : Use least privilege for service accounts will limit what permissions the exploited process gets on the rest of the system.
M1050 Exploit Protection (for T1190) : Web Application Firewalls may be used to limit exposure of applications to prevent exploit traffic from reaching the application.
M1035 Limit Access to Resource Over Network (for T1190) : Ensure that all publicly exposed services are actually intended to be so, and restrict access to any that should only be available internally.
M1051 Update Software (for T1190) : Update software regularly by employing patch management for externally exposed applications.

Detection Generic guidance

Initial Access: Alert on unusual requests to the affected service (odd paths, oversized payloads, exploit strings) in WAF, reverse-proxy and application logs.

Response checklist Generic guidance

Inventory: find every instance of the affected product and version (include internet-facing and forgotten ones).
Patch or mitigate per the vendor advisory; if you cannot patch, remove internet exposure or apply the vendor workaround.
Assume compromise if the system was exposed before patching: hunt for the indicators in the advisory and review logs back to the disclosure date.
Rotate credentials and secrets stored on or used by the affected system if compromise cannot be ruled out.