CVE-2018-6557: The MOTD update script in the base-files package in Ubuntu 18.04 LTS before 10.1ubuntu2.2, and Ubuntu 18.10 be

Routine

HIGH 7.0WATCHLISTDOWNGRADEMITIGATE

CVE-2018-6557 is a high-severity flaw (CVSS 7.0) affecting base-files, ubuntu linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The MOTD update script in the base-files package in Ubuntu 18.04 LTS before 10.1ubuntu2.2, and Ubuntu 18.10 before 10.1ubuntu6 incorrectly handled temporary files. A local attacker could use this issue to cause a denial of service, or possibly escalate privileges if kernel symlink restrictions were disabled.

Why this priority

High severity
On your watchlist

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	7.0 (High)
Attack vector	Local
Attack complexity	High
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.4% (top 69%)
CISA exploited list	No
Weakness	CWE-59
Published	2018-08-21
Last modified	2026-06-17

Publisher (CNA): Canonical Ltd. · Vendor: base-files project · canonical

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

Am I affected?

Timeline

2018-08-21 16:29 UTCPublished CVE record published
2026-06-17 02:02 UTCUpdated Record last modified

base-files project base-files DOWNGRADE

Affected: 10.1ubuntu2.2

Fixed in: no fixed release known

Safe to downgrade to: a release before 10.1ubuntu2.2

1. Check installed version

apt-cache policy base-files || rpm -q base-files || base-files --version

2. No fixed release: DOWNGRADE to a release before 10.1ubuntu2.2 (Debian / Ubuntu)

apt-cache madison base-files sudo apt install base-files=<VERSION_BEFORE_10.1ubuntu2.2> sudo apt-mark hold base-files

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list base-files sudo dnf downgrade base-files-<VERSION_BEFORE_10.1ubuntu2.2> sudo dnf versionlock add base-files

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.

canonical ubuntu linux MITIGATE

Affected: 18.04 · 18.10

Fixed in: no fixed release known

Safe to downgrade to: a release before 18.04

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-2018-6557?

base-files: downgrade or apply the listed mitigation; ubuntu linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2018-6557 being exploited?

CVE-2018-6557 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-2018-6557 affect?

CVE-2018-6557 affects base-files, ubuntu linux. Severity is high (CVSS 7.0). The MOTD update script in the base-files package in Ubuntu 18.04 LTS before 10.1ubuntu2.2, and Ubuntu 18.10 before 10.1ubuntu6 incorrectly handled temporary files. A local attacker could use this issue to cause a denial of service, or possi

How urgent is CVE-2018-6557?

Priority 37/100. High severity; On your watchlist

Software pages

Ubuntu vulnerabilities

References

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