The overlayfs implementation in the linux kernel did not properly validate with respect to user namespaces the setting of file capabilities on files in an underlying file system. Due to the combination of unprivileged user namespaces along with a patch carried in the Ubuntu kernel to allow unprivileged overlay mounts, an attacker could use this to gain elevated privileges.

The remote Ubuntu 16.04 LTS / 18.04 LTS host has a package installed that is affected by multiple vulnerabilities as referenced in the USN-4916-1 advisory.

    It was discovered that the overlayfs implementation in the Linux kernel did not properly validate the     application of file system capabilities with respect to user namespaces. A local attacker could use this     to gain elevated privileges. (CVE-2021-3493)

    Piotr Krysiuk discovered that the BPF JIT compiler for x86 in the Linux kernel did not properly validate     computation of branch displacements in some situations. A local attacker could use this to cause a denial     of service (system crash) or possibly execute arbitrary code. (CVE-2021-29154)

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 / 20.04 LTS host has a package installed that is affected by multiple vulnerabilities as referenced in the USN-4917-1 advisory.

    It was discovered that the overlayfs implementation in the Linux kernel did not properly validate the     application of file system capabilities with respect to user namespaces. A local attacker could use this     to gain elevated privileges. (CVE-2021-3493)

    Vincent Dehors discovered that the shiftfs file system in the Ubuntu Linux kernel did not properly handle     faults in copy_from_user() when passing through ioctls to an underlying file system. A local attacker     could use this to cause a denial of service (memory exhaustion) or execute arbitrary code. (CVE-2021-3492)

    Piotr Krysiuk discovered that the BPF JIT compiler for x86 in the Linux kernel did not properly validate     computation of branch displacements in some situations. A local attacker could use this to cause a denial     of service (system crash) or possibly execute arbitrary code. (CVE-2021-29154)

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 20.04 LTS host has a package installed that is affected by multiple vulnerabilities as referenced in the USN-4915-1 advisory.

    It was discovered that the overlayfs implementation in the Linux kernel did not properly validate the     application of file system capabilities with respect to user namespaces. A local attacker could use this     to gain elevated privileges. (CVE-2021-3493)

    Vincent Dehors discovered that the shiftfs file system in the Ubuntu Linux kernel did not properly handle     faults in copy_from_user() when passing through ioctls to an underlying file system. A local attacker     could use this to cause a denial of service (memory exhaustion) or execute arbitrary code. (CVE-2021-3492)

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
148691	Ubuntu 16.04 LTS / 18.04 LTS : Linux kernel vulnerabilities (USN-4916-1)	Nessus	Ubuntu Local Security Checks	high
148690	Ubuntu 18.04 LTS / 20.04 LTS : Linux kernel vulnerabilities (USN-4917-1)	Nessus	Ubuntu Local Security Checks	high
148689	Ubuntu 20.04 LTS : Linux kernel (OEM) vulnerabilities (USN-4915-1)	Nessus	Ubuntu Local Security Checks	high

Detections

Analytics

CVE-2021-3493

high

Tenable Plugins

high

high

high