CyberSecBulletin
CVE-2026-31392NVD status: Modified

Linux: Improper Authentication

Published Updated By the CyberSecBulletin desk

CVE-2026-31392 is a high-severity improper authentication vulnerability in Linux, with a CVSS 3.1 base score of 8.1 out of 10. It can be exploited with local access to the system by an attacker with administrator privileges, without any action from a user. The record lists versions fd4547830720647d4af02ee50f883c4b1cca06e4, 9229709ec8bf85ae7ca53aeee9aa14814cdc1bd2, d33cbf0bf8979d779900da9be2505d68d9d8da25 as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.12% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update Linux to fd4547830720647d4af02ee50f883c4b1cca06e4 or 9229709ec8bf85ae7ca53aeee9aa14814cdc1bd2 or d33cbf0bf8979d779900da9be2505d68d9d8da25 or 9ee803bfdba0cf739038dbdabdd4c02582c8f2b2, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 2.6.33 or 2.6.35 or 6.1.167 or 6.6.130, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinux4ff67b720c02c36e54d55b88c2931879b7db1cd2 up to, but not including, fd4547830720647d4af02ee50f883c4b1cca06e4; 4ff67b720c02c36e54d55b88c2931879b7db1cd2 up to, but not including, 9229709ec8bf85ae7ca53aeee9aa14814cdc1bd2; 4ff67b720c02c36e54d55b88c2931879b7db1cd2 up to, but not including, d33cbf0bf8979d779900da9be2505d68d9d8da25; 4ff67b720c02c36e54d55b88c2931879b7db1cd2 up to, but not including, 9ee803bfdba0cf739038dbdabdd4c02582c8f2b2; 4ff67b720c02c36e54d55b88c2931879b7db1cd2 up to, but not including, 6e9ff1eb7feedcf46ff2d0503759960ab58e7775; 4ff67b720c02c36e54d55b88c2931879b7db1cd2 up to, but not including, 12b4c5d98cd7ca46d5035a57bcd995df614c14e1; 223c7f082d2836ac719b3b228bdcfab35e5e5330; 88720224330a655ab6268e20109b65b11cfd7f6a; and 3 more rangesfd4547830720647d4af02ee50f883c4b1cca06e4, 9229709ec8bf85ae7ca53aeee9aa14814cdc1bd2, d33cbf0bf8979d779900da9be2505d68d9d8da25, 9ee803bfdba0cf739038dbdabdd4c02582c8f2b2, 6e9ff1eb7feedcf46ff2d0503759960ab58e7775, 12b4c5d98cd7ca46d5035a57bcd995df614c14e1
LinuxLinux Kernel2.6.32.44 up to, but not including, 2.6.33; 2.6.34.12 up to, but not including, 2.6.35; 2.6.36 up to, but not including, 6.1.167; 6.2 up to, but not including, 6.6.130; 6.7 up to, but not including, 6.12.78; 6.13 up to, but not including, 6.18.20; 6.19 up to, but not including, 6.19.10; 7.02.6.33, 2.6.35, 6.1.167, 6.6.130, 6.12.78, 6.18.20

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
LocalThe attacker needs local access or must trick a user into running something.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
HighAdministrator-level access is required first.
User interaction
NoneNo action by a victim is required.
Scope
ChangedThe attack can reach beyond the vulnerable component into other systems.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
LowPerformance or availability is reduced.

Vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:L. Scored by CNA.

Official description

In the Linux kernel, the following vulnerability has been resolved: smb: client: fix krb5 mount with username option Customer reported that some of their krb5 mounts were failing against a single server as the client was trying to mount the shares with wrong credentials. It turned out the client was reusing SMB session from first mount to try mounting the other shares, even though a different username= option had been specified to the other mounts. By using username mount option along with sec=krb5 to search for principals from keytab is supported by cifs.upcall(8) since cifs-utils-4.8. So fix this by matching username mount option in match_session() even with Kerberos. For example, the second mount below should fail with -ENOKEY as there is no 'foobar' principal in keytab (/etc/krb5.keytab). The client ends up reusing SMB session from first mount to perform the second one, which is wrong. ``` $ ktutil ktutil: add_entry -password -p testuser -k 1 -e aes256-cts Password for [email protected]: ktutil: write_kt /etc/krb5.keytab ktutil: quit $ klist -ke Keytab name: FILE:/etc/krb5.keytab KVNO Principal ---- ---------------------------------------------------------------- 1 [email protected] (aes256-cts-hmac-sha1-96) $ mount.cifs //w22-root2/scratch /mnt/1 -o sec=krb5,username=testuser $ mount.cifs //w22-root2/scratch /mnt/2 -o sec=krb5,username=foobar $ mount -t cifs | grep -Po 'username=\K\w+' testuser testuser ```

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Improper Authentication

When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.

How developers prevent this class of flaw

  • Use an authentication framework or library such as the OWASP ESAPI Authentication feature.

More Improper Authentication vulnerabilities (CWE-287)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Recent Improper Authentication vulnerabilities

Spotted an error? Tell us.