A flaw was found in the Linux kernel where map_write() in kernel/user_namespace.c allows privilege escalation as it mishandles nested user namespaces with more than 5 UID or GID ranges. An unprivileged user with CAP_SYS_ADMIN in an affected user namespace can bypass access controls on resources outside the namespace. This is possible because a user/group id transformation takes place properly for the namespaced-to-kernel direction but not for the kernel-to-namespaced direction.
Find out more about CVE-2018-18955 from the MITRE CVE dictionary dictionary and NIST NVD.
NOTE: The following CVSS v3 metrics and score provided are preliminary and subject to review.
| CVSS3 Base Score | 7.8 |
|---|---|
| CVSS3 Base Metrics | CVSS:3.0/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H |
| Attack Vector | Local |
| Attack Complexity | High |
| Privileges Required | Low |
| User Interaction | None |
| Scope | Changed |
| Confidentiality | High |
| Integrity Impact | High |
| Availability Impact | High |
| Platform | Package | State |
|---|---|---|
| Red Hat Enterprise MRG 2 | kernel-rt | Not affected |
| Red Hat Enterprise Linux 7 | kernel-alt | Not affected |
| Red Hat Enterprise Linux 7 | kernel | Not affected |
| Red Hat Enterprise Linux 7 | kernel-rt | Not affected |
| Red Hat Enterprise Linux 6 | kernel | Not affected |
| Red Hat Enterprise Linux 5 | kernel | Not affected |
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