Path traversal and files overwrite with unsquashfs

Singularity (an open source container platform) from version 3.1.1 through 3.6.3 has a vulnerability. Due to insecure handling of path traversal and the lack of path sanitization within `unsquashfs`, it is possible to overwrite/create any files on the host filesystem during the extraction with a crafted squashfs filesystem. The extraction occurs automatically for unprivileged (either installation or with `allow setuid = no`) run of Singularity when a user attempt to run an image which is a local SIF image or a single file containing a squashfs filesystem and is coming from remote sources `library://` or `shub://`. Image build is also impacted in a more serious way as it can be used by a root user, allowing an attacker to overwrite/create files leading to a system compromise, so far bootstrap methods `library`, `shub` and `localimage` are triggering the squashfs extraction. This issue is addressed in Singularity 3.6.4. All users are advised to upgrade to 3.6.4 especially if they use Singularity mainly for building image as root user. There is no solid workaround except to temporary avoid to use unprivileged mode with single file images in favor of sandbox images instead. Regarding image build, temporary avoid to build from `library` and `shub` sources and as much as possible use `--fakeroot` or a VM for that.

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:N

对路径名的限制不恰当(路径遍历)

Singularity 路径遍历漏洞

Singularity是Singularity 团队（Singularity）的一个开源的容器管理平台。该软件支持在其桌面上构建应用程序，并在任何公共云上或在计算边缘运行数百或数千个实例。 Singularity 3.1.1版本至3.6.3版本存在安全漏洞，该漏洞源于对路径遍历的处理不安全，并且在unsquashfs中缺少路径清理。攻击者可利用该漏洞squashfs文件系统覆盖/创建主机文件系统上的任何文件。

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