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CVE-2026-53383· NVD / CVE Program· CNA Linux

ksmbd: reject non-VALID session in compound request branch

Noroxi assessment

Priority: Monitor (action score 30/100)

  • 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: 0.66% (FIRST EPSS); higher than 51.1% of all records.
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: Linux Linux 06e1f05a1dbe8bbd054c0927b17fc0a61cc8bef7, 25ff12b82a376ff5c4583102a63d2456a6b9ebb9, 5.15.211.
  • Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to Linux Linux 06e1f05a1dbe8bbd054c0927b17fc0a61cc8bef7, 25ff12b82a376ff5c4583102a63d2456a6b9ebb9, 5.15.211 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: ksmbd: reject non-VALID session in compound request branch smb2_check_user_session() takes a shortcut for any operation that is not the first in a COMPOUND request: it reuses work->sess (the session bound by the first operation) and validates only the SessionId, then returns "valid". It never re-checks work->sess->state == SMB2_SESSION_VALID, and a SessionId of 0xFFFFFFFFFFFFFFFF (ULLONG_MAX, the MS-SMB2 related-operation value) skips even the id comparison. The standalone path (ksmbd_session_lookup_all() plus the SESSION_SETUP state machine) does enforce the VALID state; the compound branch bypasses all of it. A SESSION_SETUP carrying only an NTLM Type-1 (NtLmNegotiate) blob publishes a fresh SMB2_SESSION_IN_PROGRESS session whose sess->user is still NULL (->user is assigned later, by ntlm_authenticate()). Used as operation 1 of a COMPOUND with operation 2 = TREE_CONNECT (related, SessionId=ULLONG_MAX, \\host\IPC$), the tree-connect then runs on that IN_PROGRESS session and reaches ksmbd_ipc_tree_connect_request(), which dereferences user_name(sess->user) with sess->user == NULL (transport_ipc.c:687/701/704) -> remote NULL-pointer dereference and a kernel Oops that wedges the ksmbd worker for all clients. Reject any non-first compound operation that lands on a session which is not SMB2_SESSION_VALID, mirroring the validity the standalone lookup path enforces. SESSION_SETUP itself legitimately runs on an IN_PROGRESS session, but it is never carried as a non-first compound operation, so multi-leg authentication is unaffected by this check.

HighCVSS 7.5 · v3.1—No exploit Fix available
Published
Jul 19, 2026
Updated
Aug 17, 2026
EPSS
0.6% · 51th percentile

Report tools

JSON

Action score

30

Monitor

Low priority for now.

CVSS
30 / 40 · 7.5 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.6%

CNA vs NVD score

NVD
—
CNA · Linux
7.5
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.

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  • 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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When you'll hear from us

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  • when exploit code appears or is weaponized
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  • when EPSS rises 20 points in a week

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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.

VendorProduct
linuxlinux kernel

Affected versions

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

  • linux linux kernel5.15.121 and later · before 5.15.211
  • linux linux kernel6.1.36 and later · before 6.1.177
  • linux linux kernel6.3.10 and later · before 6.4
  • linux linux kernel6.4.1 and later · before 6.6.144
  • linux linux kernel6.7 and later · before 6.12.95
  • linux linux kernel6.13 and later · before 6.18.37
  • linux linux kernel6.19 and later · before 7.0.14
  • linux linux kernel7.1 and later · before 7.1.2
  • linux linux kernel6.4

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

    • d1066c1b3663401cd23c0d6e60cdae750ce00c0f, 6.4affected
    • eb947403518ea3d93f6d89264bb1f5416bb0c7d0 and later · before 25ff12b82a376ff5c4583102a63d2456a6b9ebb9affected · git
    • 854156d12caa9d36de1cf5f084591c7686cc8a9d and later · before fc578523a72cb8b329d32070b95898e81613cc3faffected · git
    • 5005bcb4219156f1bf7587b185080ec1da08518e and later · before d2bbbb6c55812220fee5d801c275cc267ea3cbebaffected · git
    • 5005bcb4219156f1bf7587b185080ec1da08518e and later · before 8f0302fb691537d33ec8f668565257ea9d340ffeaffected · git
    • 5005bcb4219156f1bf7587b185080ec1da08518e and later · before 7cad3ceaf679c55bc9946685dacafce78ce6b51aaffected · git
    • 5005bcb4219156f1bf7587b185080ec1da08518e and later · before 06e1f05a1dbe8bbd054c0927b17fc0a61cc8bef7affected · git
    • 5005bcb4219156f1bf7587b185080ec1da08518e and later · before 5f983b864d3d473ac533b2f4f44a1bbe5dcbccf4affected · git
    • 5005bcb4219156f1bf7587b185080ec1da08518e and later · before 609ca17d869d04ba249e32cdcbf13c0b1c66f43caffected · git
    • 5.15.121 and later · before 5.15.211affected · semver

Package-level exposure

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

EcosystemPackageAffected rangeFix
Debian:12linuxbefore 6.1.177-16.1.177-1
Debian:13linuxbefore 6.12.95-16.12.95-1
Debian:14linuxbefore 7.0.14-17.0.14-1
openSUSE:Tumbleweedkernel-sourcebefore 7.1.4-1.17.1.4-1.1

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2022-0847A flaw was found in the way the "flags" member of the new pipe buffer structure was lacking proper initialization in copy_page_to_iter_pipe KEV
    89Now
  • CVE-2021-22555Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACEKEV
    85Now
  • CVE-2016-5195Race condition in mm/gup.c in the Linux kernel 2.x through 4.x before 4.8.3 allows local users to gain privileges by leveraging incorrect haKEV
    83Now

Published before and after this one in the same product

  • ← EarlierCVE-2026-53380Jul 19, 2026 · media: rzv2h-ivc: Fix concurrent buffer list access
    31Monitor
  • ← EarlierCVE-2026-53382Jul 19, 2026 · media: vidtv: fix NULL pointer dereference in vidtv_mux_push_si
    22Monitor
  • Later →CVE-2026-53385Jul 19, 2026 · vc_screen: fix null-ptr-deref in vcs_notifier() during concurrent vcs_write
    22Monitor

Remediation

Which version to upgrade to

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

Product / packageFixed versionSource
Linux Linux06e1f05a1dbe8bbd054c0927b17fc0a61cc8bef7Vendor (CNA)
Linux Linux25ff12b82a376ff5c4583102a63d2456a6b9ebb9Vendor (CNA)
Linux Linux5.15.211Vendor (CNA)
Linux Linux5f983b864d3d473ac533b2f4f44a1bbe5dcbccf4Vendor (CNA)
Linux Linux6.1.177Vendor (CNA)
Linux Linux6.4Vendor (CNA)
Linux Linux609ca17d869d04ba249e32cdcbf13c0b1c66f43cVendor (CNA)
Linux Linux7cad3ceaf679c55bc9946685dacafce78ce6b51aVendor (CNA)
Linux Linux8f0302fb691537d33ec8f668565257ea9d340ffeVendor (CNA)
Linux Linuxd2bbbb6c55812220fee5d801c275cc267ea3cbebVendor (CNA)
Linux Linuxfc578523a72cb8b329d32070b95898e81613cc3fVendor (CNA)
debian:linux6.1.177-1 · Debian:12Package registry (OSV)
opensuse:kernel-source7.1.4-1.1 · openSUSE:TumbleweedPackage 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.

No nightly-computed relations.

Chain candidates

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

—

Bug bounty scope

No known public program.

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

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

All national notices →

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
none
Integrity
none
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
None
Integrity impact
None
Availability impact
High

Weakness class (CWE)

CWE-476 · NULL Pointer Dereference

CVSS vector

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

nvd-secondary

Attack context

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

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

  1. Fix✗ → ✓

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

References

Show all references (7 more)

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

All records