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CVE-2021-3493

Status Candidate

Overview

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.

Related Files

Ubuntu Overlayfs Local Privilege Escalation
Posted Dec 3, 2021
Authored by bwatters-r7, ssd-disclosure | Site metasploit.com

This Metasploit module exploits a vulnerability in Ubuntu's implementation of overlayfs. The vulnerability is the result of failing to verify the ability of a user to set the attributes in a running executable. Specifically, when Overlayfs sends the set attributes data to the underlying file system via vfs_setxattr, it fails to first verify the data by calling cap_convert_nscap. This vulnerability was patched by moving the call to cap_convert_nscap into the vfs_setxattr function that sets the attribute, forcing verification every time the vfs_setxattr is called rather than trusting the data was already verified.

tags | exploit
systems | linux, ubuntu
advisories | CVE-2021-3493
SHA-256 | db2db701a06e20ebab9c0759df9c3b43a3146ecf6b60cce3c13e3d0541420302
Ubuntu OverlayFS Local Privilege Escalation
Posted May 31, 2021
Authored by Chris Wild, Sudhanshu Kumar, Rohit Verma

The document in this archive illustrates using the included proof of concept exploit to achieve root on Ubuntu systems using a flaw in the OverlayFS file system. The exploit itself does not have author attribution as the proof of concept came through SSD Disclosures.

tags | exploit, paper, root, proof of concept
systems | linux, ubuntu
advisories | CVE-2021-3493
SHA-256 | 7380c1055909d23c493abb4f5067d3428e536c6a0041025856be420b9c8732fb
Kernel Live Patch Security Notice LSN-0076-1
Posted May 3, 2021
Authored by Benjamin M. Romer

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. 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.

tags | advisory, denial of service, arbitrary, x86, kernel, local
systems | linux
advisories | CVE-2021-29154, CVE-2021-3493
SHA-256 | 2804a214253fb2c002641f38c8aae9e4023d617f9897b0c5c01ff06e5794df2b
Ubuntu Security Notice USN-4916-2
Posted Apr 22, 2021
Authored by Ubuntu | Site security.ubuntu.com

Ubuntu Security Notice 4916-2 - USN-4916-1 fixed vulnerabilities in the Linux kernel. Unfortunately, the fix for CVE-2021-3493 introduced a memory leak in some situations. This update fixes the problem. 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. Various other issues were also addressed.

tags | advisory, kernel, local, vulnerability, memory leak
systems | linux, ubuntu
advisories | CVE-2021-29154, CVE-2021-3493
SHA-256 | 0109aef37883b59cfde530823abac56b2ccc7f8d9cf5d79c37274335d1792a6c
Ubuntu Security Notice USN-4917-1
Posted Apr 16, 2021
Authored by Ubuntu | Site security.ubuntu.com

Ubuntu Security Notice 4917-1 - 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. 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 or execute arbitrary code. Various other issues were also addressed.

tags | advisory, denial of service, arbitrary, kernel, local
systems | linux, ubuntu
advisories | CVE-2021-29154, CVE-2021-3492, CVE-2021-3493
SHA-256 | 0960410ba7e6e4040775aa7d07813ed851354f20fef02f6247a7d3b53d08796a
Ubuntu Security Notice USN-4916-1
Posted Apr 16, 2021
Authored by Ubuntu | Site security.ubuntu.com

Ubuntu Security Notice 4916-1 - 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. 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 or possibly execute arbitrary code. Various other issues were also addressed.

tags | advisory, denial of service, arbitrary, x86, kernel, local
systems | linux, ubuntu
advisories | CVE-2021-29154, CVE-2021-3493
SHA-256 | 731316af4af43b6a4f4a4888d410c88049b391c7650608ca1fd2ed0566f0f141
Ubuntu Security Notice USN-4915-1
Posted Apr 16, 2021
Authored by Ubuntu | Site security.ubuntu.com

Ubuntu Security Notice 4915-1 - 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. 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 or execute arbitrary code. Various other issues were also addressed.

tags | advisory, denial of service, arbitrary, kernel, local
systems | linux, ubuntu
advisories | CVE-2021-3492, CVE-2021-3493
SHA-256 | 2b1839252b77d24d87a54b70638bd57f0a4ba7b2d54f60cbe703b38834363ae3
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