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Public proof of conceptFix available

CVE-2026-4408

A public proof of concept exists; no exploitation attested.

  • Published2026-05-28
  • WeaknessCWE-78

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

A flaw was found in Samba. A remote attacker can exploit a misconfiguration in Samba file servers and classic domain controllers that use the "check password script" feature. If this script is configured with the %u substitution character, the client-controlled username is passed without proper escaping of shell meta-characters. This vulnerability allows an attacker to achieve remote command execution on the affected system. This issue primarily affects non-standard configurations where the "check password script" is used with %u and the samba-dcerpcd service is started as a system service.

Timeline

dates in UTC
  1. 2026-05-2809:16CVE publishedNVD
  2. 2026-10-2319:23First public proof of conceptPoC-in-GitHub

Observed activity

isMalicious corpus · updated 2026-10-23 18:48 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2026-4408?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2026-4408?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD
Redhat enterprise linux
BranchAffectedFixed in
6.0= 6.0no fix published
7.0= 7.0no fix published
9.0= 9.0no fix published
Redhat openshift container platform
BranchAffectedFixed in
4.0= 4.0no fix published
Samba
BranchAffectedFixed in
4.x≥ 4.1.0, < 4.21.04.21.0

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Vendor advisories

  • RHSA-2026:59831 Red Hat Product Security1 product fixed

    Red Hat Security Advisory: OpenShift Container Platform 4.12.97 bug fix and security update

Full record on NVD

Fix

  1. Vendor fix Red Hat Product Security RHSA-2026:59831 · 1 productFor OpenShift Container Platform 4.12 see the following documentation, which will be updated shortly for this release, for important instructions on how to upgrade your cluster and fully apply this asynchronous errata update: https://docs.redhat.com/en/documentation/openshift_container_platform/4.…
  2. Workaround from the vendor Red Hat Product Security RHSA-2026:59831 · 1 productMitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.

Advisories and patches

Detection

read 2026-10-23 19:25 UTC
Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
1 repository, unverifiedSafeBreach-Labs/ForgottenButNotGone
PoC-in-GitHub

Sources

  • CISA-ADPSSVC decisionnone2026-05-29
  • OpenCVESSVC decisionnone—
  • CNACVSS 3.19read 2026-10-23
  • NVDCVSS 3.19.8read 2026-10-23
  • CNAweakness (CWE)CWE-78read 2026-10-23
  • FIRST EPSSEPSS score1.8 %2026-10-22
  • PoC-in-GitHubproof of concept1read 2026-10-23

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Published
2026-05-28
Last Modified
2026-10-08
NVD status
Modified

Frequently asked questions

What is CVE-2026-4408?

A flaw was found in Samba. A remote attacker can exploit a misconfiguration in Samba file servers and classic domain controllers that use the "check password script" feature. If this script is configured with the %u substitution character, the client-controlled username is passed without proper escaping of shell meta-characters. This vulnerability allows an attacker to achieve remote command execution on the affected system. This issue primarily affects non-standard configurations where the "check password script" is used with %u and the samba-dcerpcd service is started as a system service.

Is CVE-2026-4408 actively exploited?

Active exploitation of CVE-2026-4408 has not been confirmed. Its EPSS score was 1.8% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-4408?

CVE-2026-4408 has a CVSS v3 base score of 9.8 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

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