CVE-2018-18586: chmextract.c in the chmextract sample program, as distributed with libmspack before 0.8alpha, does not protect

This week

MEDIUM 5.3REMOTEDOWNGRADE

CVE-2018-18586 is a medium-severity flaw (CVSS 5.3) affecting libmspack. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

chmextract.c in the chmextract sample program, as distributed with libmspack before 0.8alpha, does not protect against absolute/relative pathnames in CHM files, leading to Directory Traversal. NOTE: the vendor disputes that this is a libmspack vulnerability, because chmextract.c was only intended as a source-code example, not a supported application

Why this priority

Public exploit reference
Remotely exploitable, no login, no user action

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

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	3.3% (top 12%)
CISA exploited list	No
Weakness	CWE-22
Published	2018-10-23
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: kyzer

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

Am I affected?

Timeline

2018-10-23 02:29 UTCPublished CVE record published
2026-06-17 01:47 UTCUpdated Record last modified

kyzer libmspack DOWNGRADE

Affected: 0.3 alpha · 0.4 alpha · 0.5 alpha · 0.6 alpha · 0.7 alpha

Fixed in: no fixed release known

Safe to downgrade to: a release before 0.3

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 0.3 (Debian / Ubuntu)

apt-cache madison libmspack sudo apt install libmspack=<VERSION_BEFORE_0.3> sudo apt-mark hold libmspack

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

dnf --showduplicates list libmspack sudo dnf downgrade libmspack-<VERSION_BEFORE_0.3> sudo dnf versionlock add libmspack

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.

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-2018-18586?

libmspack: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2018-18586 being exploited?

CVE-2018-18586 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-2018-18586 affect?

CVE-2018-18586 affects libmspack. Severity is medium (CVSS 5.3). chmextract.c in the chmextract sample program, as distributed with libmspack before 0.8alpha, does not protect against absolute/relative pathnames in CHM files, leading to Directory Traversal. NOTE: the vendor disputes that this is a libmsp

How urgent is CVE-2018-18586?

Priority 51/100. Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

CVE-2019-1010305 MEDIUM 5.5 DOWNGRADE MITIGATE libmspack 0.9.1alpha is affected by: Buffer Overflow
CVE-2018-18585 MEDIUM 4.3 DOWNGRADE MITIGATE chmd_read_headers in mspack/chmd.c in libmspack before 0.8alpha accepts a filename that has '\0' as its first
CVE-2018-18584 MEDIUM 6.5 UPGRADE DOWNGRADE In mspack/cab.h in libmspack before 0.8alpha and cabextract before 1.8, the CAB block input buffer is one byte
CVE-2018-14682 HIGH 8.8 DOWNGRADE UPGRADE An issue was discovered in mspack/chmd.c in libmspack before 0.7alpha
CVE-2018-14681 HIGH 8.8 DOWNGRADE UPGRADE An issue was discovered in kwajd_read_headers in mspack/kwajd.c in libmspack before 0.7alpha

References

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