Date: Thu, 15 Apr 2021 14:31:14 -0700 From: Steve Beattie <steve.beattie@...onical.com> To: oss-security@...ts.openwall.com Subject: [CVE-2021-3493] Ubuntu Linux kernel overlayfs fs caps privilege escalation Hello, An independent security researcher reported via the SSD Secure Disclosure program that the overlayfs stacking file system within the Linux kernel as used within Ubuntu did not properly validate the application of file capabilities against user namespaces. This issue is likely Ubuntu specific, as Ubuntu carries a patch to enable unprivileged overlayfs mounts. The combination of that patch plus allowing unprivileged user namespaces by default in Ubuntu allows an unprivileged attacker to gain elevated privileges. A commit that addresses the issue was applied in the upstream kernel: 7c03e2cda4a5 ("vfs: move cap_convert_nscap() call into vfs_setxattr()") (v5.10) It was added prior to the upstream kernel commit allowing unprivileged overlayfs mounts: 459c7c565ac3 ("ovl: unprivieged mounts") (v5.11) Thus the upstream Linux kernel is not affected. -- Steve Beattie <sbeattie@...ntu.com> Download attachment "signature.asc" of type "application/pgp-signature" (834 bytes)
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