What is CVE-2017-18206?

CVE-2017-18206 is a critical-severity vulnerability in Zsh, classified under Improper Restriction of Operations within the Bounds of a Memory Buffer. CVSS score: 9.8/10. Published 2018-02-27.

How severe is CVE-2017-18206?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Buffer overflow in Zsh

CVE-2017-18206

In utils.c in zsh before 5.4, symlink expansion had a buffer overflow.

Vulnerability class: Buffer Overflow

Published 2018-02-27 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.031 (87.4th percentile), scored 2026-10-06.

Low probability of exploitation in the next 30 days, but still tracked. 87th percentile — 87.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.031 · newest: 0.031 · change: 0.000

Affected products

Zsh
Canonical Ubuntu Linux — versions 14.04, 16.04, 17.10

Weakness classification (CWE)

CWE-119 — Improper Restriction of Operations within the Bounds of a Memory Buffer

References

usn.ubuntu.com/3593-1/ (vendor-advisory, Third Party Advisory)
security.gentoo.org/glsa/201805-10 (vendor-advisory, Third Party Advisory)
access.redhat.com/errata/RHSA-2018:1932 (vendor-advisory, Third Party Advisory)
sourceforge.net/p/zsh/code/ci/c7a9cf465dd620ef48d586026944d9bd7a0d5d6d (Patch, Third Party Advisory)
access.redhat.com/errata/RHSA-2018:3073 (vendor-advisory, Third Party Advisory)
lists.debian.org/debian-lts-announce/2020/12/msg00000.html (mailing-list)

Frequently asked questions

What is CVE-2017-18206?: CVE-2017-18206 is a critical-severity vulnerability in Zsh, classified under Improper Restriction of Operations within the Bounds of a Memory Buffer. CVSS score: 9.8/10. Published 2018-02-27.
How severe is CVE-2017-18206?: Critical severity. CVSS v3 base score is 9.8 out of 10.