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CVE-2023-4091: A vulnerability was discovered in Samba, where the flaw allows SMB clients to truncate files, even with read-o

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This month
MEDIUM 6.5WATCHLISTUPGRADEMITIGATEDOWNGRADE

CVE-2023-4091 is a medium-severity flaw (CVSS 6.5) affecting samba, fedora, storage. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A vulnerability was discovered in Samba, where the flaw allows SMB clients to truncate files, even with read-only permissions when the Samba VFS module "acl_xattr" is configured with "acl_xattr:ignore system acls = yes". The SMB protocol allows opening files when the client requests read-only access but then implicitly truncates the opened file to 0 bytes if the client specifies a separate OVERWRITE create disposition request. The issue arises in

Why this priority

  • On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score6.5 (Medium)
Attack vectorNetwork (remote)
Attack complexityLow
Privileges neededLow
User interactionNone
EPSS exploit chance1.3% (top 29%)
CISA exploited listNo
WeaknessCWE-276
Published2023-11-03
Last modified2026-06-17
Publisher (CNA): Red Hat, Inc. · Vendor: fedoraproject · redhat · samba

Share: LinkedIn · X · Reddit

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

samba samba UPGRADE
Affected: < 4.17.12 · >= 4.18.0 and < 4.18.8 · >= 4.19.0 and < 4.19.1
Fixed in: 4.17.12, 4.18.8, 4.19.1
Safe to downgrade to: a release before 4.18.0
1. Check installed version
apt-cache policy samba || rpm -q samba || samba --version
2. UPGRADE to 4.17.12 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade samba
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade samba
Note
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
3. If no update is available yet, DOWNGRADE to a release before 4.18.0 (Debian / Ubuntu)
apt-cache madison samba sudo apt install samba=<VERSION_BEFORE_4.18.0> sudo apt-mark hold samba
3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list samba sudo dnf downgrade samba-<VERSION_BEFORE_4.18.0> sudo dnf versionlock add samba
Downgrade risk
Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.
After downgrade
Restart the service, and keep the package held until a fixed release ships.
fedoraproject fedora MITIGATE
Affected: 39
Fixed in: no fixed release known
Safe to downgrade to: a release before 39
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
redhat storage DOWNGRADE
Affected: 3.0
Fixed in: no fixed release known
Safe to downgrade to: a release before 3.0
1. Check installed version
apt-cache policy storage || rpm -q storage || storage --version
2. No fixed release: DOWNGRADE to a release before 3.0 (Debian / Ubuntu)
apt-cache madison storage sudo apt install storage=<VERSION_BEFORE_3.0> sudo apt-mark hold storage
2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list storage sudo dnf downgrade storage-<VERSION_BEFORE_3.0> sudo dnf versionlock add storage
Downgrade risk
Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.
After downgrade
Restart the service, and keep the package held until a fixed release ships.
redhat enterprise linux MITIGATE
Affected: 8.0
Fixed in: no fixed release known
Safe to downgrade to: a release before 8.0
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
redhat enterprise linux eus MITIGATE
Affected: 9.0
Fixed in: no fixed release known
Safe to downgrade to: a release before 9.0
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2023-4091?

samba: upgrade to 4.17.12, 4.18.8, 4.19.1; fedora: mitigate or apply the listed mitigation; storage: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2023-4091 being exploited?

CVE-2023-4091 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2023-4091 affect?

CVE-2023-4091 affects samba, fedora, storage. Severity is medium (CVSS 6.5). A vulnerability was discovered in Samba, where the flaw allows SMB clients to truncate files, even with read-only permissions when the Samba VFS module "acl_xattr" is configured with "acl_xattr:ignore system acls = yes". The SMB protocol al

How urgent is CVE-2023-4091?

Priority 46/100. On your watchlist

Software pages

Samba vulnerabilities

Related CVEs

References

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