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.

The remote Ubuntu 16.04 LTS host has a package installed that is affected by multiple vulnerabilities as referenced in the USN-3836-2 advisory.

    USN-3836-1 fixed vulnerabilities in the Linux kernel for Ubuntu 18.04 LTS. This update provides the     corresponding updates for the Linux Hardware Enablement (HWE) kernel from Ubuntu 18.04 LTS for Ubuntu     16.04 LTS.

    Jann Horn discovered that the Linux kernel mishandles mapping UID or GID ranges inside nested user     namespaces in some situations. A local attacker could use this to bypass access controls on resources     outside the namespace. (CVE-2018-18955)

    Philipp Wendler discovered that the overlayfs implementation in the Linux kernel did not properly verify     the directory contents permissions from within a unprivileged user namespace. A local attacker could use     this to expose sensitive information (protected file names). (CVE-2018-6559)

Tenable has extracted the preceding description block directly from the Ubuntu security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The remote Ubuntu 18.04 LTS host has a package installed that is affected by multiple vulnerabilities as referenced in the USN-3836-1 advisory.

    Jann Horn discovered that the Linux kernel mishandles mapping UID or GID ranges inside nested user     namespaces in some situations. A local attacker could use this to bypass access controls on resources     outside the namespace. (CVE-2018-18955)

    Philipp Wendler discovered that the overlayfs implementation in the Linux kernel did not properly verify     the directory contents permissions from within a unprivileged user namespace. A local attacker could use     this to expose sensitive information (protected file names). (CVE-2018-6559)

Tenable has extracted the preceding description block directly from the Ubuntu security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

Jann Horn discovered that the procfs file system implementation in the Linux kernel did not properly restrict the ability to inspect the kernel stack of an arbitrary task. A local attacker could use this to expose sensitive information. (CVE-2018-17972)

Jann Horn discovered that the mremap() system call in the Linux kernel did not properly flush the TLB when completing, potentially leaving access to a physical page after it has been released to the page allocator. A local attacker could use this to cause a denial of service (system crash), expose sensitive information, or possibly execute arbitrary code. (CVE-2018-18281)

It was discovered that the BPF verifier in the Linux kernel did not correctly compute numeric bounds in some situations. A local attacker could use this to cause a denial of service (system crash) or possibly execute arbitrary code. (CVE-2018-18445)

Daniel Dadap discovered that the module loading implementation in the Linux kernel did not properly enforce signed module loading when booted with UEFI Secure Boot in some situations. A local privileged attacker could use this to execute untrusted code in the kernel.
(CVE-2018-18653)

Jann Horn discovered that the Linux kernel mishandles mapping UID or GID ranges inside nested user namespaces in some situations. A local attacker could use this to bypass access controls on resources outside the namespace. (CVE-2018-18955)

Philipp Wendler discovered that the overlayfs implementation in the Linux kernel did not properly verify the directory contents permissions from within a unprivileged user namespace. A local attacker could use this to expose sensitive information (protected file names). (CVE-2018-6559).

Note that Tenable Network Security has extracted the preceding description block directly from the Ubuntu security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

The remote Ubuntu 18.04 LTS host has a package installed that is affected by multiple vulnerabilities as referenced in the USN-3833-1 advisory.

    Jann Horn discovered that the Linux kernel mishandles mapping UID or GID ranges inside nested user     namespaces in some situations. A local attacker could use this to bypass access controls on resources     outside the namespace. (CVE-2018-18955)

    Philipp Wendler discovered that the overlayfs implementation in the Linux kernel did not properly verify     the directory contents permissions from within a unprivileged user namespace. A local attacker could use     this to expose sensitive information (protected file names). (CVE-2018-6559)

Tenable has extracted the preceding description block directly from the Ubuntu security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

ID	Name	Product	Family	Severity
119340	Ubuntu 16.04 LTS : Linux kernel (HWE) vulnerabilities (USN-3836-2)	Nessus	Ubuntu Local Security Checks	high
119339	Ubuntu 18.04 LTS : Linux kernel vulnerabilities (USN-3836-1)	Nessus	Ubuntu Local Security Checks	high
119338	Ubuntu 18.10 : linux, linux-gcp, linux-kvm, linux-raspi2 vulnerabilities (USN-3835-1)	Nessus	Ubuntu Local Security Checks	high
119303	Ubuntu 18.04 LTS : Linux kernel (AWS) vulnerabilities (USN-3833-1)	Nessus	Ubuntu Local Security Checks	high
119302	Ubuntu 18.10 : Linux kernel (AWS) vulnerabilities (USN-3832-1)	Nessus	Ubuntu Local Security Checks	high

Detections

Analytics

CVE-2018-18955

high

Tenable Plugins

high

high

high

high

high