CVE-2017-18205: In builtin.c in zsh before 5.4, when sh compatibility mode is used, there is a NULL pointer dereference during

Q: How do I fix CVE-2017-18205?

zsh: upgrade to 5.4. Exact commands for each OS are on this page.

Q: Is CVE-2017-18205 being exploited?

CVE-2017-18205 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-2017-18205 affect?

CVE-2017-18205 affects zsh. Severity is high (CVSS 8.1). In builtin.c in zsh before 5.4, when sh compatibility mode is used, there is a NULL pointer dereference during processing of the cd command with no argument if HOME is not set.

Q: How urgent is CVE-2017-18205?

Priority 54/100. High severity; Remotely exploitable, no login, no user action

This month

HIGH 8.1REMOTEUPGRADE

CVE-2017-18205 is a high-severity flaw (CVSS 8.1) affecting zsh. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

In builtin.c in zsh before 5.4, when sh compatibility mode is used, there is a NULL pointer dereference during processing of the cd command with no argument if HOME is not set.

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	8.1 (High)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	2.0% (top 19%)
CISA exploited list	No
Weakness	CWE-476
Published	2018-02-27
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: zsh project

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 01:12 UTCUpdated Record last modified

zsh project zsh UPGRADE

Affected: < 5.4

Fixed in: 5.4

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 5.4 (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.

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-2017-18205?

zsh: upgrade to 5.4. Exact commands for each OS are on this page.

Is CVE-2017-18205 being exploited?

CVE-2017-18205 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-2017-18205 affect?

CVE-2017-18205 affects zsh. Severity is high (CVSS 8.1). In builtin.c in zsh before 5.4, when sh compatibility mode is used, there is a NULL pointer dereference during processing of the cd command with no argument if HOME is not set.

How urgent is CVE-2017-18205?

Priority 54/100. High severity; Remotely exploitable, no login, no user action

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References

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