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Date: Fri, 16 Nov 2018 00:38:18 +0100
From: Jann Horn <>
Subject: Linux kernel: broken uid/gid mapping for nested user namespaces with
 >5 ranges (CVE-2018-18955; since 4.15; fixed in 4.18.19 and 4.19.2)

NOTE: I have requested a CVE identifier, and I'm sending this message,
to make tracking of the fix easier; however, to avoid missing security
fixes without CVE identifiers, you should *NOT* be cherry-picking a
specific patch in response to a notification about a kernel security

In Linux kernel versions since 4.15, map_write() in
kernel/user_namespace.c handles nested user namespaces with more than
5 UID or GID ranges incorrectly. This can allow a user who has
CAP_SYS_ADMIN in a user namespace which maps at least 6 UIDs or GIDs
to bypass access controls on resources outside the namespace.

This is CVE-2018-18955.

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