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NVD / CVE Program· CNA Linux

CVE-2026-31712: ksmbd: require minimum ACE size in smb_check_perm_dacl()

HighCVSS 8.3 · v3.1—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 33/100)

  • 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: 0.32% (FIRST EPSS).
  • Anyone who can reach it over the internet can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: Linux Linux 151b1799861fde38087c08f613abc2843ef597b0, 282cbbb476b9f35793452bc461934af4c7eca169, 325d4ac11f526cb8964cff14548ccf02d8c756d8.

Low priority for now. Upgrade to Linux Linux 151b1799861fde38087c08f613abc2843ef597b0, 282cbbb476b9f35793452bc461934af4c7eca169, 325d4ac11f526cb8964cff14548ccf02d8c756d8 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: require minimum ACE size in smb_check_perm_dacl() Both ACE-walk loops in smb_check_perm_dacl() only guard against an under-sized remaining buffer, not against an ACE whose declared `ace->size` is smaller than the struct it claims to describe: if (offsetof(struct smb_ace, access_req) > aces_size) break; ace_size = le16_to_cpu(ace->size); if (ace_size > aces_size) break; The first check only requires the 4-byte ACE header to be in bounds; it does not require access_req (4 bytes at offset 4) to be readable. An attacker who has set a crafted DACL on a file they own can declare ace->size == 4 with aces_size == 4, pass both checks, and then granted |= le32_to_cpu(ace->access_req); /* upper loop */ compare_sids(&sid, &ace->sid); /* lower loop */ reads access_req at offset 4 (OOB by up to 4 bytes) and ace->sid at offset 8 (OOB by up to CIFS_SID_BASE_SIZE + SID_MAX_SUB_AUTHORITIES * 4 bytes). Tighten both loops to require ace_size >= offsetof(struct smb_ace, sid) + CIFS_SID_BASE_SIZE which is the smallest valid on-wire ACE layout (4-byte header + 4-byte access_req + 8-byte sid base with zero sub-auths). Also reject ACEs whose sid.num_subauth exceeds SID_MAX_SUB_AUTHORITIES before letting compare_sids() dereference sub_auth[] entries. parse_sec_desc() already enforces an equivalent check (lines 441-448); smb_check_perm_dacl() simply grew weaker validation over time. Reachability: authenticated SMB client with permission to set an ACL on a file. On a subsequent CREATE against that file, the kernel walks the stored DACL via smb_check_perm_dacl() and triggers the OOB read. Not pre-auth, and the OOB read is not reflected to the attacker, but KASAN reports and kernel state corruption are possible.

Published
May 1, 2026
Updated
Nov 11, 2026
EPSS
0.3% · 25th percentile

Report tools

JSON

Action score

33

Monitor

Low priority for now.

CVSS
33 / 40 · 8.3 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.3%

CNA vs NVD score

NVD
—
CNA · Linux
8.3
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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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

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

    • 5.15affected
    • 6.1.176 and later · up to and including 6.1.*not affected · semver
    • 6.6.140 and later · up to and including 6.6.*not affected · semver
    • 6.12.84 and later · up to and including 6.12.*not affected · semver
    • 6.18.25 and later · up to and including 6.18.*not affected · semver
    • 7.0.2 and later · up to and including 7.0.*not affected · semver
    • 7.1 and laternot affected · original_commit_for_fix
    • before 5.15not affected · semver
    • 5.15.210 and later · up to and including 5.15.*not affected · semver
    • e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 and later · before 282cbbb476b9f35793452bc461934af4c7eca169affected · git

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 and later · before 6.12.84
  • linux linux kernel6.13 and later · before 6.18.25
  • linux linux kernel6.19 and later · before 7.0.2

Package-level exposure

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

EcosystemPackageAffected rangeFix
Debian:12linuxbefore 6.1.176-16.1.176-1
Debian:13linuxbefore 6.12.85-16.12.85-1
Debian:14linuxbefore 7.0.3-17.0.3-1
openSUSE:Tumbleweedkernel-sourcebefore 7.0.7-1.17.0.7-1.1

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-31431crypto: algif_aead - Revert to operating out-of-placeKEV
    90Now
  • 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

Published before and after this one in the same product

  • ← EarlierCVE-2026-31710May 1, 2026 · smb: client: fix dir separator in SMB1 UNIX mounts
    22Monitor
  • ← EarlierCVE-2026-31711May 1, 2026 · smb: server: fix active_num_conn leak on transport allocation failure
    30Monitor
  • Later →CVE-2026-31714May 1, 2026 · f2fs: fix to avoid memory leak in f2fs_rename()
    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 Linux151b1799861fde38087c08f613abc2843ef597b0Vendor (CNA)
Linux Linux282cbbb476b9f35793452bc461934af4c7eca169Vendor (CNA)
Linux Linux325d4ac11f526cb8964cff14548ccf02d8c756d8Vendor (CNA)
Linux Linux90089584b2e25c4510b7b987387b4405f0673eceVendor (CNA)
Linux Linux95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4cVendor (CNA)
Linux Linuxd07b26f39246a82399661936dd0c853983cfade7Vendor (CNA)
Linux Linuxf20adc4ef7428bc485ee83fd1a592252fb87718bVendor (CNA)
debian:linux6.1.176-1 · Debian:12Package registry (OSV)
opensuse:kernel-source7.0.7-1.1 · 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.

Not on record for this CVE: EPSS history · patch commit or PR link · researcher credit · variant or chain candidate · public bounty program.

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
low · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
Low
Availability impact
High

Weakness class (CWE)

CWE-787 · Out-of-bounds Write

CVSS vector

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

References

Show all references (7 more)

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

All records