Skip to main content
Public proof of conceptFix available

CVE-2018-18955

A public proof of concept exists; no exploitation attested.

  • Published2018-11-16
  • WeaknessCWE-863

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

In the Linux kernel 4.15.x through 4.19.x before 4.19.2, map_write() in kernel/user_namespace.c allows privilege escalation because it mishandles nested user namespaces with more than 5 UID or GID ranges. A user who has CAP_SYS_ADMIN in an affected user namespace can bypass access controls on resources outside the namespace, as demonstrated by reading /etc/shadow. This occurs because an ID transformation takes place properly for the namespaced-to-kernel direction but not for the kernel-to-namespaced direction.

Timeline

dates in UTC
  1. 2018-11-16Exploit-DB entryExploit-DB
  2. 2018-11-1620:29CVE publishedNVD

Versions per branch

NVD
Canonical ubuntu linux
BranchAffectedFixed in
16.4= 16.04no fix published
18.4= 18.04no fix published
18.10= 18.10no fix published
Linux linux kernel
BranchAffectedFixed in
4.x≥ 4.15, < 4.19.24.19.2

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • linuxUbuntu:18.04:LTSall versions · fixed in 4.15.0-42.45
  • linuxDebian:14all versions · fixed in 4.18.20-1
  • linuxDebian:13all versions · fixed in 4.18.20-1
  • linuxDebian:12all versions · fixed in 4.18.20-1
  • linux-awsUbuntu:18.04:LTSall versions · fixed in 4.15.0-1029.30
  • linux-azureUbuntu:18.04:LTSall versions · fixed in 4.15.0-1035.36
  • linux-azureUbuntu:16.04:LTSall versions · fixed in 4.15.0-1035.36~16.04.1
  • linux-azureUbuntu:14.04:LTSall versions · fixed in 4.15.0-1035.36~14.04.2

6 more package ranges on OSV.dev

Vendor advisories

  • CVE-2018-18955 Red Hat Product Security

    kernel: Privilege escalation in map_write() in kernel/user_namespace.c

Full record on NVD

Fix

Advisories and patches

Detection

read 2026-11-01 01:02 UTC
Nuclei template
none so far
ProjectDiscovery
Exploit-DB
EDB-45886EDB-45915EDB-47164EDB-47165EDB-47166EDB-47167
Exploit-DB
Proof of concept
Metasploit modules
1 moduleexploit/linux/local/nested_namespace_idmap_limit_priv_escrank: greatModule metadata: Metasploit Framework, © Rapid7, Inc., BSD-3-Clause.
Metasploit Framework

Sources

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.0/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
Published
2018-11-16
Last Modified
2026-06-17
NVD status
Modified

Frequently asked questions

What is CVE-2018-18955?

In the Linux kernel 4.15.x through 4.19.x before 4.19.2, map_write() in kernel/user_namespace.c allows privilege escalation because it mishandles nested user namespaces with more than 5 UID or GID ranges. A user who has CAP_SYS_ADMIN in an affected user namespace can bypass access controls on resources outside the namespace, as demonstrated by reading /etc/shadow. This occurs because an ID transformation takes place properly for the namespaced-to-kernel direction but not for the kernel-to-namespaced direction.

Is CVE-2018-18955 actively exploited?

Active exploitation of CVE-2018-18955 has not been confirmed. Its EPSS score was 7.7% on 2026-11-04, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2018-18955?

CVE-2018-18955 has a CVSS v3 base score of 7 (HIGH severity), with vector string CVSS:3.0/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H.

Running Linux kernel? Hear about its next vulnerability

Surveillance reads the versions in your stack — a domain, a lockfile or a list — checks each CVE against the ranges its sources publish, and alerts you when one you run is exploited or enters CISA KEV. A version it cannot read stays « version not verified ».

Get alerts for this productCISA KEV additions, November 2026Search CVEs

No credit card required · No monthly cap on website lookups · 250 API requests/month

Go further

Related vulnerabilities

Same product first, then the same vendor advisory and the same publication week.

Back to CVE Database

Sources for this record