CVE-2018-15856: An infinite loop when reaching EOL unexpectedly in compose/parser.c (aka the keymap parser) in xkbcommon befor

Q: How do I fix CVE-2018-15856?

xkbcommon: upgrade to 0.8.1; ubuntu linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Q: Is CVE-2018-15856 being exploited?

CVE-2018-15856 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-2018-15856 affect?

CVE-2018-15856 affects xkbcommon, ubuntu linux. Severity is medium (CVSS 5.5). An infinite loop when reaching EOL unexpectedly in compose/parser.c (aka the keymap parser) in xkbcommon before 0.8.1 could be used by local attackers to cause a denial of service during parsing of crafted keymap files.

Q: How urgent is CVE-2018-15856?

Priority 34/100. On your watchlist

Routine

MEDIUM 5.5WATCHLISTUPGRADEMITIGATE

CVE-2018-15856 is a medium-severity flaw (CVSS 5.5) affecting xkbcommon, ubuntu linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

An infinite loop when reaching EOL unexpectedly in compose/parser.c (aka the keymap parser) in xkbcommon before 0.8.1 could be used by local attackers to cause a denial of service during parsing of crafted keymap files.

Why this priority

On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	5.5 (Medium)
Attack vector	Local
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.4% (top 63%)
CISA exploited list	No
Weakness	CWE-835
Published	2018-08-25
Last modified	2026-06-17

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

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

Am I affected?

Timeline

2018-08-25 21:29 UTCPublished CVE record published
2026-06-17 01:43 UTCUpdated Record last modified

xkbcommon xkbcommon UPGRADE

Affected: < 0.8.1

Fixed in: 0.8.1

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 0.8.1 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade xkbcommon

Note

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

canonical ubuntu linux MITIGATE

Affected: 14.04 · 16.04 · 18.04

Fixed in: no fixed release known

Safe to downgrade to: a release before 14.04

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-2018-15856?

xkbcommon: upgrade to 0.8.1; ubuntu linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2018-15856 being exploited?

CVE-2018-15856 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-2018-15856 affect?

CVE-2018-15856 affects xkbcommon, ubuntu linux. Severity is medium (CVSS 5.5). An infinite loop when reaching EOL unexpectedly in compose/parser.c (aka the keymap parser) in xkbcommon before 0.8.1 could be used by local attackers to cause a denial of service during parsing of crafted keymap files.

How urgent is CVE-2018-15856?

Priority 34/100. On your watchlist

Software pages

Ubuntu vulnerabilities

Related CVEs

CVE-2018-15864 MEDIUM 5.5 UPGRADE UPGRADE Unchecked NULL pointer usage in resolve_keysym in xkbcomp/parser.y in xkbcommon before 0.8.2 could be used by
CVE-2018-15863 MEDIUM 5.5 UPGRADE UPGRADE Unchecked NULL pointer usage in ResolveStateAndPredicate in xkbcomp/compat.c in xkbcommon before 0.8.2 could b
CVE-2018-15862 MEDIUM 5.5 UPGRADE UPGRADE Unchecked NULL pointer usage in LookupModMask in xkbcomp/expr.c in xkbcommon before 0.8.2 could be used by loc
CVE-2018-15861 MEDIUM 5.5 UPGRADE UPGRADE Unchecked NULL pointer usage in ExprResolveLhs in xkbcomp/expr.c in xkbcommon before 0.8.2 could be used by lo
CVE-2018-15859 MEDIUM 5.5 UPGRADE UPGRADE Unchecked NULL pointer usage when parsing invalid atoms in ExprResolveLhs in xkbcomp/expr.c in xkbcommon befor

References

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