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.
Does this matter?
6 public exploits are published in Exploit-DB (verified) and the impact is high, while EPSS rates exploitation at 7.6%. Anyone can run this; patch or mitigate before the next change window and check exposed instances for signs of use.
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.
- CVSS 3.0
- 7.0 HIGHCVSS:3.0/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
- EPSS
- 7.61% probability · 95th percentile
- Public exploits
- 6 in Exploit-DB · verified · first 16 November 2018
- CISA KEV
- Not listed
- Weakness
- CWE-863
- Affected
- linux/linux kernel · canonical/ubuntu linux
- Source
- cve@mitre.org
EPSS moved from 17.3% on 21 September 2026 to 7.6% on 27 October 2026. The dashed line is the ten per cent mark our analysts treat as “patch before the next change window”.
Public exploits (6)
Entries in Exploit-DB that cite this CVE. Links go to the Exploit-DB page and to the file in the public repository; nothing is hosted here. A verified tick means the Exploit-DB team confirmed the exploit works against the stated version.
| EDB-ID | Title | Type | Published | Verified |
|---|---|---|---|---|
| EDB-47167source ↗ | Linux Kernel 4.15.x < 4.19.2 - 'map_write() CAP_SYS_ADMIN' Local Privilege Escalation (polkit Method)linux · bcoles | local | 4 January 2019 | no |
| EDB-47165source ↗ | Linux Kernel 4.15.x < 4.19.2 - 'map_write() CAP_SYS_ADMIN' Local Privilege Escalation (dbus Method)linux · bcoles | local | 4 January 2019 | no |
| EDB-45915source ↗ | Linux - Nested User Namespace idmap Limit Local Privilege Escalation (Metasploit)linux · Metasploit | local | 29 November 2018 | yes |
| EDB-47166source ↗ | Linux Kernel 4.15.x < 4.19.2 - 'map_write() CAP_SYS_ADMIN' Local Privilege Escalation (ldpreload Method)linux · bcoles | local | 21 November 2018 | no |
| EDB-47164source ↗ | Linux Kernel 4.15.x < 4.19.2 - 'map_write() CAP_SYS_ADMIN' Local Privilege Escalation (cron Method)linux · bcoles | local | 21 November 2018 | no |
| EDB-45886source ↗ | Linux - Broken uid/gid Mapping for Nested User Namespaceslinux · Google Security Research | local | 16 November 2018 | yes |
References
- http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=d2f007dbe7e4c9583eea6eb04d60001e85c6f1bdPatch, Vendor Advisory
- http://www.securityfocus.com/bid/105941Third Party Advisory, VDB Entry
- https://bugs.chromium.org/p/project-zero/issues/detail?id=1712Patch, Third Party Advisory
- https://cdn.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.18.19Patch, Vendor Advisory
- https://cdn.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.19.2Patch, Vendor Advisory
- https://github.com/torvalds/linux/commit/d2f007dbe7e4c9583eea6eb04d60001e85c6f1bdPatch, Vendor Advisory
- https://security.netapp.com/advisory/ntap-20190416-0003/
- https://support.f5.com/csp/article/K39103040
- https://usn.ubuntu.com/3832-1/Third Party Advisory
- https://usn.ubuntu.com/3833-1/Third Party Advisory
- https://usn.ubuntu.com/3835-1/Third Party Advisory
- https://usn.ubuntu.com/3836-1/Third Party Advisory
- https://usn.ubuntu.com/3836-2/Third Party Advisory
- https://www.exploit-db.com/exploits/45886/Exploit, Patch, Third Party Advisory, VDB Entry
- https://www.exploit-db.com/exploits/45915/Exploit, Third Party Advisory, VDB Entry
- http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=d2f007dbe7e4c9583eea6eb04d60001e85c6f1bdPatch, Vendor Advisory
- http://www.securityfocus.com/bid/105941Third Party Advisory, VDB Entry
- https://bugs.chromium.org/p/project-zero/issues/detail?id=1712Patch, Third Party Advisory
- https://cdn.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.18.19Patch, Vendor Advisory
- https://cdn.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.19.2Patch, Vendor Advisory
- https://github.com/torvalds/linux/commit/d2f007dbe7e4c9583eea6eb04d60001e85c6f1bdPatch, Vendor Advisory
- https://security.netapp.com/advisory/ntap-20190416-0003/
- https://support.f5.com/csp/article/K39103040
- https://usn.ubuntu.com/3832-1/Third Party Advisory
- https://usn.ubuntu.com/3833-1/Third Party Advisory
- https://usn.ubuntu.com/3835-1/Third Party Advisory
- https://usn.ubuntu.com/3836-1/Third Party Advisory
- https://usn.ubuntu.com/3836-2/Third Party Advisory
- https://www.exploit-db.com/exploits/45886/Exploit, Patch, Third Party Advisory, VDB Entry
- https://www.exploit-db.com/exploits/45915/Exploit, Third Party Advisory, VDB Entry
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.