smb: client: fix krb5 mount with username option

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Summary

CVECVE-2026-31392
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-03 16:16:37 UTC
Updated2026-04-27 14:16:35 UTC
DescriptionIn 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 ```

Risk And Classification

Primary CVSS: v3.1 8.1 HIGH from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

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

EPSS: 0.000320000 probability, percentile 0.092090000 (date 2026-04-27)

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary8.1HIGHCVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:L
3.1CNADECLARED8.1HIGHCVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:L

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
High
User Interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
Low

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 4ff67b720c02c36e54d55b88c2931879b7db1cd2 fd4547830720647d4af02ee50f883c4b1cca06e4 git Not specified
CNA Linux Linux affected 4ff67b720c02c36e54d55b88c2931879b7db1cd2 9229709ec8bf85ae7ca53aeee9aa14814cdc1bd2 git Not specified
CNA Linux Linux affected 4ff67b720c02c36e54d55b88c2931879b7db1cd2 d33cbf0bf8979d779900da9be2505d68d9d8da25 git Not specified
CNA Linux Linux affected 4ff67b720c02c36e54d55b88c2931879b7db1cd2 9ee803bfdba0cf739038dbdabdd4c02582c8f2b2 git Not specified
CNA Linux Linux affected 4ff67b720c02c36e54d55b88c2931879b7db1cd2 6e9ff1eb7feedcf46ff2d0503759960ab58e7775 git Not specified
CNA Linux Linux affected 4ff67b720c02c36e54d55b88c2931879b7db1cd2 12b4c5d98cd7ca46d5035a57bcd995df614c14e1 git Not specified
CNA Linux Linux affected 223c7f082d2836ac719b3b228bdcfab35e5e5330 git Not specified
CNA Linux Linux affected 88720224330a655ab6268e20109b65b11cfd7f6a git Not specified
CNA Linux Linux affected 2.6.36 Not specified
CNA Linux Linux unaffected 2.6.36 semver Not specified
CNA Linux Linux unaffected 6.1.167 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.130 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.78 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.20 6.18.* semver Not specified
CNA Linux Linux unaffected 6.19.10 6.19.* semver Not specified
CNA Linux Linux unaffected 7.0 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/fd4547830720647d4af02ee50f883c4b1cca06e4 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/d33cbf0bf8979d779900da9be2505d68d9d8da25 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/6e9ff1eb7feedcf46ff2d0503759960ab58e7775 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/12b4c5d98cd7ca46d5035a57bcd995df614c14e1 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/9ee803bfdba0cf739038dbdabdd4c02582c8f2b2 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/9229709ec8bf85ae7ca53aeee9aa14814cdc1bd2 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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