CVE-2018-7548: In subst.c in zsh through 5.4.2, there is a NULL pointer dereference when using ${(PA)...} on an empty array r

Q: How do I fix CVE-2018-7548?

zsh: upgrade to newer than 5.4.2; ubuntu linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Q: Is CVE-2018-7548 being exploited?

CVE-2018-7548 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2018-7548 affect?

CVE-2018-7548 affects zsh, ubuntu linux. Severity is critical (CVSS 9.8). In subst.c in zsh through 5.4.2, there is a NULL pointer dereference when using ${(PA)...} on an empty array result.

Q: How urgent is CVE-2018-7548?

Priority 66/100. Critical severity; Remotely exploitable, no login, no user action; On your watchlist

This week

CRITICAL 9.8REMOTEWATCHLISTUPGRADEMITIGATE

CVE-2018-7548 is a critical-severity flaw (CVSS 9.8) affecting zsh, ubuntu linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

In subst.c in zsh through 5.4.2, there is a NULL pointer dereference when using ${(PA)...} on an empty array result.

Why this priority

Critical severity
Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	2.5% (top 15%)
CISA exploited list	No
Weakness	CWE-476
Published	2018-02-27
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: canonical · zsh

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

Am I affected?

Timeline

2018-02-27 22:29 UTCPublished CVE record published
2026-06-17 02:03 UTCUpdated Record last modified

zsh zsh UPGRADE

Affected: <= 5.4.2

Fixed in: newer than 5.4.2

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy zsh || rpm -q zsh || zsh --version

2. UPGRADE to newer than 5.4.2 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade zsh

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade zsh

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

canonical ubuntu linux MITIGATE

Affected: 17.10

Fixed in: no fixed release known

Safe to downgrade to: a release before 17.10

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-2018-7548?

zsh: upgrade to newer than 5.4.2; ubuntu linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2018-7548 being exploited?

CVE-2018-7548 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-2018-7548 affect?

CVE-2018-7548 affects zsh, ubuntu linux. Severity is critical (CVSS 9.8). In subst.c in zsh through 5.4.2, there is a NULL pointer dereference when using ${(PA)...} on an empty array result.

How urgent is CVE-2018-7548?

Priority 66/100. Critical severity; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Ubuntu vulnerabilities

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References

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