Finding Samba instances with vulnerable vfs_fruit
A new vulnerability has surfaced in Samba, which has the potential to provide unauthenticated remote code execution to attackers. Popular as Windows-compatible file sharing and print services software via the SMB protocol, Samba typically runs under Linux and other non-Windows OSes. You can usually find Samba on servers, appliances, desktops, and IoT devices. This out-of-bounds heap read write vulnerability (tracked as CVE-2021-44142 with a “critical” CVSS score of 9.9) resides in Samba’s
vfs_fruit module and was discovered-and-disclosed by security researchers Nguyễn Hoàng Thạch and Billy Jheng Bing-Jhong, along with Lucas Leong, and also separately by security researcher Orange Tsai.
For this vulnerability to be successfully exploitable by an attacker, the
vfs_fruit module must be in use with default configuration settings for the
fruit:resource options. The attacker must also have write access to a file share (which could allow guests and unauthenticated users, based on the configuration) that supports extended attributes (i.e.,
ea support = yes, which is the default for Samba).
While the list of potentially vulnerable vendors is lengthy, some formerly-vulnerable major Linux distributions have patches available, including Red Hat, Ubuntu, and SUSE. Samba maintainers have also released patched versions, and they recommened everyone upgrade to Samba version 4.13.17, 4.14.12, or 4.15.5 as soon as possible. In the event that upgrading is not possible, Samba maintainers offer a mitigation path: removing the “fruit” VFS module from the list of configured VFS objects in any “vfs objects” line in the Samba smb.conf configuration file.
protocol:smb and (product:samba or smb.sessionID:="0x00000000%")
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