Auth bypass in Linux Kernel

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.

Vulnerability class: Broken Access Control

EPSS: 0.076 (93.9th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 7.0 (High). Vector: CVSS:3.0/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H.

Affected products

Weakness classification (CWE)

Public proof-of-concept exploits

References

  • cve@mitre.org (Patch, x_refsource_MISC, Vendor Advisory)
  • cve@mitre.org (Patch, x_refsource_MISC, Vendor Advisory)
  • cve@mitre.org (x_refsource_UBUNTU, vendor-advisory, Third Party Advisory)
  • cve@mitre.org (x_refsource_UBUNTU, vendor-advisory, Third Party Advisory)
  • cve@mitre.org (Patch, Third Party Advisory, x_refsource_MISC)
  • cve@mitre.org (Patch, x_refsource_MISC, Vendor Advisory)
  • cve@mitre.org (x_refsource_UBUNTU, vendor-advisory, Third Party Advisory)
  • cve@mitre.org (x_refsource_UBUNTU, vendor-advisory, Third Party Advisory)
  • cve@mitre.org (Exploit, VDB Entry, Third Party Advisory, exploit, x_refsource_EXPLOIT-DB)
  • cve@mitre.org (Patch, x_refsource_MISC, Vendor Advisory)

Frequently asked questions

What is CVE-2018-18955?
CVE-2018-18955 is a high-severity vulnerability in Linux Kernel, classified under Incorrect Authorization. CVSS score: 7.0/10. Published 2018-11-16.
How severe is CVE-2018-18955?
High severity. CVSS v3 base score is 7.0 out of 10.
Is CVE-2018-18955 known to be exploited?
42 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.