Linux Kernel up to 7.0-rc4 SMB Client /etc/krb5.keytab match_session weak password hash

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5.7$0-$5k0.00

Summaryinfo

A vulnerability has been found in Linux Kernel up to 7.0-rc4 and classified as critical. The affected element is the function match_session of the file /etc/krb5.keytab of the component SMB Client. This manipulation causes weak password hash. This vulnerability is handled as CVE-2026-31392. There is not any exploit available. The affected component should be upgraded.

Detailsinfo

A vulnerability classified as problematic was found in Linux Kernel up to 7.0-rc4. Affected by this vulnerability is the function match_session of the file /etc/krb5.keytab of the component SMB Client. The manipulation with an unknown input leads to a weak password hash vulnerability. The CWE definition for the vulnerability is CWE-916. The product generates a hash for a password, but it uses a scheme that does not provide a sufficient level of computational effort that would make password cracking attacks infeasible or expensive. As an impact it is known to affect confidentiality. The summary by CVE is:

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 ```

The advisory is shared at git.kernel.org. This vulnerability is known as CVE-2026-31392 since 03/09/2026. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1552 for this issue.

The vulnerability scanner Nessus provides a plugin with the ID 311783 (Debian dla-4561 : linux-config-6.1 - security update), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.1.167, 6.6.130, 6.12.78, 6.18.20, 6.19.10 or 7.0-rc5 eliminates this vulnerability. Applying the patch fd4547830720647d4af02ee50f883c4b1cca06e4/9229709ec8bf85ae7ca53aeee9aa14814cdc1bd2/d33cbf0bf8979d779900da9be2505d68d9d8da25/9ee803bfdba0cf739038dbdabdd4c02582c8f2b2/6e9ff1eb7feedcf46ff2d0503759960ab58e7775/12b4c5d98cd7ca46d5035a57bcd995df614c14e1 is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at Tenable (311783). If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Productinfo

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CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 5.8
VulDB Meta Temp Score: 5.7

VulDB Base Score: 3.5
VulDB Temp Score: 3.4
VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA Base Score: 8.1
CNA Vector (Linux): 🔒

CVSSv2info

AVACAuCIA
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💳💳💳💳💳💳
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Weak password hash
CWE: CWE-916 / CWE-326 / CWE-310
CAPEC: 🔒
ATT&CK: 🔒

Physical: Partially
Local: Yes
Remote: Partially

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 311783
Nessus Name: Debian dla-4561 : linux-config-6.1 - security update

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 6.1.167/6.6.130/6.12.78/6.18.20/6.19.10/7.0-rc5
Patch: fd4547830720647d4af02ee50f883c4b1cca06e4/9229709ec8bf85ae7ca53aeee9aa14814cdc1bd2/d33cbf0bf8979d779900da9be2505d68d9d8da25/9ee803bfdba0cf739038dbdabdd4c02582c8f2b2/6e9ff1eb7feedcf46ff2d0503759960ab58e7775/12b4c5d98cd7ca46d5035a57bcd995df614c14e1

Timelineinfo

03/09/2026 CVE reserved
04/03/2026 +24 days Advisory disclosed
04/03/2026 +0 days VulDB entry created
05/27/2026 +54 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2026-31392 (🔒)
GCVE (CVE): GCVE-0-2026-31392
GCVE (VulDB): GCVE-100-355141

Entryinfo

Created: 04/03/2026 18:11
Updated: 05/27/2026 04:55
Changes: 04/03/2026 18:11 (60), 05/04/2026 21:37 (2), 05/27/2026 04:55 (11)
Complete: 🔍
Cache ID: 216::103

If you want to get the best quality for vulnerability data then you always have to consider VulDB.

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