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Vulnerability of Linux kernel: directory traversal via fs/nfsd/nfs3xdr.c

Synthesis of the vulnerability 

An attacker can traverse directories via fs/nfsd/nfs3xdr.c of the Linux kernel, in order to read a file outside the service root path.
Impacted systems: Debian, Fedora, Linux, Ubuntu.
Severity of this alert: 2/4.
Creation date: 27/01/2021.
Références of this alert: CERTFR-2021-AVI-149, CERTFR-2021-AVI-191, CERTFR-2021-AVI-200, CERTFR-2021-AVI-265, CVE-2021-3178, DLA-2586-1, FEDORA-2021-3bcc7198c8, USN-4753-1, USN-4876-1, USN-4877-1, USN-4878-1, USN-4910-1, USN-4912-1, VIGILANCE-VUL-34415.

Description of the vulnerability 

An attacker can traverse directories via fs/nfsd/nfs3xdr.c of the Linux kernel, in order to read a file outside the service root path.
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This security note impacts software or systems such as Debian, Fedora, Linux, Ubuntu.

Our Vigil@nce team determined that the severity of this threat announce is medium.

The trust level is of type confirmed by the editor, with an origin of internet client.

An attacker with a expert ability can exploit this computer weakness announce.

Solutions for this threat 

Linux kernel: version 5.10.10.
The version 5.10.10 is fixed:
  https://cdn.kernel.org/pub/linux/kernel/v5.x/

Linux kernel: version 5.4.92.
The version 5.4.92 is fixed:
  https://cdn.kernel.org/pub/linux/kernel/v5.x/

Linux kernel: version 4.19.170.
The version 4.19.170 is fixed:
  https://cdn.kernel.org/pub/linux/kernel/v4.x/

Linux kernel: version 4.14.217.
The version 4.14.217 is fixed:
  https://cdn.kernel.org/pub/linux/kernel/v4.x/

Linux kernel: version 4.9.253.
The version 4.9.253 is fixed:
  https://cdn.kernel.org/pub/linux/kernel/v4.x/

Linux kernel: version 4.4.253.
The version 4.4.253 is fixed:
  https://cdn.kernel.org/pub/linux/kernel/v4.x/

Linux kernel: patch for fs/nfsd/nfs3xdr.c.
A patch is indicated in information sources.

Debian 9: new linux packages.
New packages are available:
  Debian 9: linux 4.9.258-1

Fedora 33: new kernel packages.
New packages are available:
  Fedora 33: kernel 5.10.10-200.fc33

Ubuntu 20.04: new linux-image-5.10.0 packages.
New packages are available:
  Ubuntu 20.04 LTS: linux-image-oem-20.04b 5.10.0.1014.15

Ubuntu 20.04: new linux-image-oem-20.04 packages.
New packages are available:
  Ubuntu 20.04 LTS: linux-image-oem-20.04 5.6.0.1053.49

Ubuntu: new linux-image-4.15.0 packages.
New packages are available:
  Ubuntu 14.04 ESM: linux-image-azure 4.15.0.1109.82
  Ubuntu 16.04 LTS: linux-image-generic-hwe-16.04 4.15.0.137.133
  Ubuntu 18.04 LTS: linux-image-generic 4.15.0.137.124

Ubuntu: new linux-image-4.4.0 packages.
New packages are available:
  Ubuntu 14.04 ESM: linux-image-generic-lts-xenial 4.4.0.204.178
  Ubuntu 16.04 LTS: linux-image-generic 4.4.0.204.210

Ubuntu: new linux-image-5.4.0 packages.
New packages are available:
  Ubuntu 18.04 LTS: linux-image-generic-hwe-18.04 5.4.0.67.75~18.04.62
  Ubuntu 20.04 LTS: linux-image-generic 5.4.0.67.70

Ubuntu: new linux-image-5.8.0 packages.
New packages are available:
  Ubuntu 20.04 LTS: linux-image-generic-hwe-20.04 5.8.0.49.55~20.04.33
  Ubuntu 20.10: linux-image-generic 5.8.0.49.54
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