8.6

CVE-2026-31611: ksmbd: require 3 sub-authorities before reading sub_auth[2]

Modified
AliasesUBUNTU-CVE-2026-31611DEBIAN-CVE-2026-31611CGA-23cw-8qcf-9xgw
Published 24-04-2026Last modified 15-10-2026

Vulnerability summary

CVE-2026-31611 is a high (CVSS 8.6) vulnerability in linux. EPSS estimates a 0.38% chance of exploitation in the next 30 days, higher than 31.5% of scored vulnerabilities.

Priority
Prioritisesevere

Severe, CVSS 8.6 (CVE.org); no exploitation reported by the 5 checked sources; EPSS 0% (FIRST, 03-11-2026)

Source freshness unavailable

How is this decided?
CVSS score
8.6/10
010
High · v3.1 (CVE.org)
EPSS score
0.38%
0%100%
Low · -0.15 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 20 · Related 21
OPENSUSE-SU-2026:10703-1USN-8488-1USN-8488-2USN-8507-1USN-8567-1USN-8569-1

Timeline

  1. 24-04-2026
    PublishedVulnerability first disclosed.
  2. 15-10-2026
    Last modifiedVulnerability information updated.

Description

In the Linux kernel, the following vulnerability has been resolved: ksmbd: require 3 sub-authorities before reading sub_auth[2] parse_dacl() compares each ACE SID against sid_unix_NFS_mode and on match reads sid.sub_auth[2] as the file mode. If sid_unix_NFS_mode is the prefix S-1-5-88-3 with num_subauth = 2 then compare_sids() compares only min(num_subauth, 2) sub-authorities so a client SID with num_subauth = 2 and sub_auth = {88, 3} will match. If num_subauth = 2 and the ACE is placed at the very end of the security descriptor, sub_auth[2] will be 4 bytes past end_of_acl. The out-of-band bytes will then be masked to the low 9 bits and applied as the file's POSIX mode, probably not something that is good to have happen. Fix this up by forcing the SID to actually carry a third sub-authority before reading it at all.

CVSS metrics

6 scores · 5 sources · 2 versions

EPSS trend

Probability

0.38%

Chance of exploitation in the next 30 days

Percentile

32%

Versus all other CVEs

30-day change

Decrease -0.15 pp

From 0.52% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

No weakness data has been published for this record.

Affected systems

Version check

Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.

Ubuntu146 products
  • linuxAll versions (No fix recorded) | < 6.8.0-136.136 | < 7.0.0-27.27
  • linux-allwinner-5.19All versions (No fix recorded)
  • linux-awsAll versions (No fix recorded) | < 6.8.0-1061.64 | < 7.0.0-1008.8
  • linux-aws-5.0All versions (No fix recorded)
  • linux-aws-5.11All versions (No fix recorded)
Chainguard8 products
  • linux-aws-6.18< 6.18.31-r0
  • linux-azure-6.18< 6.18.31-r0
  • linux-gcp-6.18< 6.18.31-r0
  • linux-qemu-6.12< 6.12.85-r0
  • linux-qemu-6.18< 6.18.31-r0
Linux2 products
  • linux≥ e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, < cf2148b880fb7c0fcd727202dbc4fd5d6998b9c2 | ≥ e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, < b5b5d5936a50497fb151c0b122899a6894721c2b | ≥ e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, < 08f9e6d899b5c834bbcc239eae1bed58d9b15d2c | ≥ e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, < d2454f4a002d08560a60f214f392e6491cf11560 | ≥ e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, < 46bbcd3ebfb3549c8da1838fc4493e79bd3241e7 | ≥ e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, < 9401f86a224f37b50e6a3ccf1d46a70d5ef8af0a | ≥ e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9, < 53370cf9090777774e07fd9a8ebce67c6cc333ab | 5.15
  • linux_kernel≥ 5.15, < 6.6.136 | ≥ 6.7, < 6.12.83 | ≥ 6.13, < 6.18.24 | ≥ 6.19, < 6.19.14 | ≥ 7.0, < 7.0.1
Debian1 product
  • linux< 6.1.176-1 | < 6.12.85-1 | < 6.19.14-1

4 vendors · 157 products

References

34 links
Show all 34 references