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Fencer Intel
high 7.0

CVE-2018-18955 json

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 mish…

published 7y ago modified 4mo ago also EUVD-2018-10659

cvss
7.0
version 3.0, NVD
cisa kev
Not listed
not in CISA's catalog
epss
7.7%
EPSS 7.7% chance of exploitation in 30 days, percentile 94%
public exploits
7
Metasploit and Exploit-DB

Summary

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.

Patch / fix

  • linux linux_kernel 4.19.2
  • linux Debian 14, Debian 13, Debian 12 4.18.20-1

debian advisories DEBIAN-CVE-2018-18955

  • linux Ubuntu 18.04 LTS 4.15.0-42.45
  • linux-aws Ubuntu 18.04 LTS 4.15.0-1029.30
  • linux-gcp Ubuntu 16.04 LTS 4.15.0-1025.26~16.04.1
  • linux-gcp Ubuntu 18.04 LTS 4.15.0-1025.26
  • linux-hwe Ubuntu 16.04 LTS 4.15.0-42.45~16.04.1
  • linux-kvm Ubuntu 18.04 LTS 4.15.0-1027.27
  • linux-oem Ubuntu 18.04 LTS 4.15.0-1028.33
  • linux-azure Ubuntu 14.04 LTS 4.15.0-1035.36~14.04.2

ubuntu advisories UBUNTU-CVE-2018-18955

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Is CVE-2018-18955 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2018-18955 updated cvss 7.8

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

  • Red Hat Enterprise Linux 5 kernel Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, kernel-alt, python-perf, +9 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat Enterprise MRG 2 kernel-rt, mrg-rt-release, kernel-rt-trace, kernel-rt-vanilla, kernel-rt-firmware
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Timeline

  1. First public exploit (Metasploit exploit/linux/local/nested_namespace_idmap_limit_priv_esc)
  2. Published

Exploit prediction

7.67% chance of exploitation in the next 30 days, higher than 94% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • Metasploit exploit/linux/local/nested_namespace_idmap_limit_priv_esc Linux Nested User Namespace idmap Limit Local Privilege Escalation metasploit exploit, great rank, 2018-11-15
  • EDB-47167 Linux Kernel 4.15.x < 4.19.2 - 'map_write() CAP_SYS_ADMIN' Local Privilege Escalation (polkit Method) local, 2019-01-04
  • EDB-47166 Linux Kernel 4.15.x < 4.19.2 - 'map_write() CAP_SYS_ADMIN' Local Privilege Escalation (ldpreload Method) local, 2018-11-21
  • EDB-47165 Linux Kernel 4.15.x < 4.19.2 - 'map_write() CAP_SYS_ADMIN' Local Privilege Escalation (dbus Method) local, 2019-01-04
  • EDB-47164 Linux Kernel 4.15.x < 4.19.2 - 'map_write() CAP_SYS_ADMIN' Local Privilege Escalation (cron Method) local, 2018-11-21
  • EDB-45915 Linux - Nested User Namespace idmap Limit Local Privilege Escalation (Metasploit) local, 2018-11-29
  • EDB-45886 Linux - Broken uid/gid Mapping for Nested User Namespaces local, 2018-11-16

CVSS scores

assigned by version score vector
NVD 3.0 7.0 CVSS:3.0/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 4.4 AV:L/AC:M/Au:N/C:P/I:P/A:P

Classification

Weakness
Technology feeds

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.