CVE-2026-31392· NVD / CVE Program· CNA Linux

smb: client: fix krb5 mount with username option

Noroxi assessment

Priority: Monitor (action score 32/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.16% (FIRST EPSS).
Someone with local access to the system can trigger it. Administrator privileges are required. No user action is required. No special conditions are required; it is repeatable.
Fixed version: Linux Linux 12b4c5d98cd7ca46d5035a57bcd995df614c14e1, 2.6.33, 2.6.35.

Low priority for now. Upgrade to Linux Linux 12b4c5d98cd7ca46d5035a57bcd995df614c14e1, 2.6.33, 2.6.35 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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 testuser@ZELDA.TEST: ktutil: write_kt /etc/krb5.keytab ktutil: quit $ klist -ke Keytab name: FILE:/etc/krb5.keytab KVNO Principal ---- ---------------------------------------------------------------- 1 testuser@ZELDA.TEST (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 ```

HighCVSS 8.1 · v3.1—No exploit Fix available

Auth bypass

Published: Apr 3, 2026
Updated: Oct 19, 2026
EPSS: 0.1% · 5th percentile
CWE: CWE-287

Report tools

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Action score

Monitor

Low priority for now.

CVSS: 32 / 40 · 8.1 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.1%

CISA SSVC decision

Exploitation: none
Automatable: no
Technical impact: total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: —
CNA · Linux: 8.1; NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
linux	linux kernel	cpe:2.3:o:linux:linux_kernel

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

linux linux kernel2.6.32.44 and later · before 2.6.33
linux linux kernel2.6.34.12 and later · before 2.6.35
linux linux kernel2.6.36 and later · before 6.1.167
linux linux kernel6.2 and later · before 6.6.130
linux linux kernel6.7 and later · before 6.12.78
linux linux kernel6.13 and later · before 6.18.20
linux linux kernel6.19 and later · before 6.19.10
linux linux kernel7.0

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

Linux Linux
- 223c7f082d2836ac719b3b228bdcfab35e5e5330, 88720224330a655ab6268e20109b65b11cfd7f6a, 2.6.36affected
- 4ff67b720c02c36e54d55b88c2931879b7db1cd2 and later · before fd4547830720647d4af02ee50f883c4b1cca06e4affected · git
- 4ff67b720c02c36e54d55b88c2931879b7db1cd2 and later · before 9229709ec8bf85ae7ca53aeee9aa14814cdc1bd2affected · git
- 4ff67b720c02c36e54d55b88c2931879b7db1cd2 and later · before d33cbf0bf8979d779900da9be2505d68d9d8da25affected · git
- 4ff67b720c02c36e54d55b88c2931879b7db1cd2 and later · before 9ee803bfdba0cf739038dbdabdd4c02582c8f2b2affected · git
- 4ff67b720c02c36e54d55b88c2931879b7db1cd2 and later · before 6e9ff1eb7feedcf46ff2d0503759960ab58e7775affected · git
- 4ff67b720c02c36e54d55b88c2931879b7db1cd2 and later · before 12b4c5d98cd7ca46d5035a57bcd995df614c14e1affected · git
- 2.6.32.44 and later · before 2.6.33affected · semver
- 2.6.34.12 and later · before 2.6.35affected · semver
- before 2.6.36not affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Debian:12	linux	before 6.1.170-1	6.1.170-1
Debian:13	linux	before 6.12.85-1	6.12.85-1
Debian:14	linux	before 6.19.10-1	6.19.10-1
SUSE:Linux Micro 6.0	kernel-default	before 6.4.0-52.1	6.4.0-52.1
SUSE:Linux Micro 6.0	kernel-default-base	before 6.4.0-52.1.21.36	6.4.0-52.1.21.36
SUSE:Linux Micro 6.0	kernel-kvmsmall	before 6.4.0-52.1	6.4.0-52.1
SUSE:Linux Micro 6.0	kernel-rt	before 6.4.0-52.1	6.4.0-52.1
SUSE:Linux Micro 6.0	kernel-source	before 6.4.0-52.1	6.4.0-52.1
SUSE:Linux Micro 6.0	kernel-source-rt	before 6.4.0-52.1	6.4.0-52.1
SUSE:Linux Micro 6.1	kernel-default-base	before 6.4.0-52.1.21.34	6.4.0-52.1.21.34

Same product

linux: all records

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Published before and after this one in the same product

← EarlierCVE-2026-31389Apr 3, 2026 · spi: fix use-after-free on controller registration failure
31Monitor
← EarlierCVE-2026-31391Apr 3, 2026 · crypto: atmel-sha204a - Fix OOM ->tfm_count leak
22Monitor
Later →CVE-2026-31393Apr 3, 2026 · Bluetooth: L2CAP: Validate L2CAP_INFO_RSP payload length before access
32Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
Linux Linux	12b4c5d98cd7ca46d5035a57bcd995df614c14e1	Vendor (CNA)
Linux Linux	2.6.33	Vendor (CNA)
Linux Linux	2.6.35	Vendor (CNA)
Linux Linux	6e9ff1eb7feedcf46ff2d0503759960ab58e7775	Vendor (CNA)
Linux Linux	9229709ec8bf85ae7ca53aeee9aa14814cdc1bd2	Vendor (CNA)
Linux Linux	9ee803bfdba0cf739038dbdabdd4c02582c8f2b2	Vendor (CNA)
Linux Linux	d33cbf0bf8979d779900da9be2505d68d9d8da25	Vendor (CNA)
Linux Linux	fd4547830720647d4af02ee50f883c4b1cca06e4	Vendor (CNA)
debian:linux	6.1.170-1 · Debian:12	Package registry (OSV)
suse:kernel-default	6.4.0-52.1 · SUSE:Linux Micro 6.0	Package registry (OSV)
suse:kernel-default-base	6.4.0-52.1.21.36 · SUSE:Linux Micro 6.0	Package registry (OSV)
suse:kernel-kvmsmall	6.4.0-52.1 · SUSE:Linux Micro 6.0	Package registry (OSV)
suse:kernel-rt	6.4.0-52.1 · SUSE:Linux Micro 6.0	Package registry (OSV)
suse:kernel-source	6.4.0-52.1 · SUSE:Linux Micro 6.0	Package registry (OSV)
suse:kernel-source-rt	6.4.0-52.1 · SUSE:Linux Micro 6.0	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

CVE-2026-3177328 days apartBluetooth: SMP: derive legacy responder STK authentication from MITM state
35Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

CVE-2026-915582 days apartOS Command Injection in Rapid7 InsightConnect Sed Plugin via expression parameter.
35Monitor
CVE-2026-915382 days apartArbitrary File Read in Rapid7 InsightConnect Sed Plugin
26Monitor
CVE-2026-915482 days apartArbitrary File Write in Rapid7 InsightConnect Sed Plugin
26Monitor

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

Someone with local access to the system can trigger it.
Administrator privileges are required.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: high · data can be read
Integrity: high · data or configuration can be modified
Availability: low · the service can be disrupted

Impact can extend beyond the vulnerable component (scope changes).

Attack vector: Local
Attack complexity: Low
Privileges required: High
User interaction: None
Scope: Changed
Confidentiality impact: High
Integrity impact: High
Availability impact: Low

Weakness class (CWE)

CWE-287 · Improper Authentication

CVSS vector

CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:L

nvd-secondary

Root cause

Authentication is added route by route instead of being enforced in one place. When a route added later bypasses the shared middleware, the session check never runs for it.

The bug in code

The whole CWE-287 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1app.use("/admin", requireSession, adminRouter);2
3// Route added later skips the middleware4app.post("/admin-api/config", updateConfig);

Fixed

1const admin = express.Router();2admin.use(requireSession, requireRole("admin"));3
4admin.post("/config", updateConfig);5app.use("/admin", admin);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Attack patterns (CAPEC)

ATT&CK techniques

Change log

SSVC exploitation— → noneOct 16, 2026, 5:07 PM UTC
Fix✗ → ✓Sep 28, 2026, 10:11 PM UTC

For records you follow, these changes also arrive as notifications. →

References

git.kernel.org/stable/c/12b4c5d98cd7ca46d5035a57bcd995df614c14e1

Show all references (5 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records