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"value": "The SFTP subsystem must be configured with the <tt>root</tt> option in <tt>ssh_sftpd:subsystem_spec/1</tt>. The <tt>root</tt> option is not set by default."
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}
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],
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"value": "The SFTP subsystem must be configured with the root option in ssh_sftpd:subsystem_spec/1. The root option is not set by default."
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}
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],
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"credits": [
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{
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"lang": "en",
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"type": "finder",
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"value": "John Downey"
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},
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{
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"lang": "en",
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"type": "remediation developer",
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"value": "Michał Wąsowski"
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},
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{
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"lang": "en",
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"type": "remediation reviewer",
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"value": "Jakub Witczak"
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}
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],
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"descriptions": [
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{
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"lang": "en",
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"supportingMedia": [
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{
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"base64": false,
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"type": "text/html",
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"value": "Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') vulnerability in Erlang OTP <tt>ssh</tt> (<tt>ssh_sftpd</tt> module) allows an authenticated SFTP user to modify file attributes outside the configured chroot directory.<p>The SFTP daemon (<tt>ssh_sftpd</tt>) stores the raw, user-supplied path in file handles instead of the chroot-resolved path. When <tt>SSH_FXP_FSETSTAT</tt> is issued on such a handle, file attributes (permissions, ownership, timestamps) are modified on the real filesystem path, bypassing the root directory boundary entirely.</p><p>Any authenticated SFTP user on a server configured with the <tt>root</tt> option can modify file attributes of files outside the intended chroot boundary. The prerequisite is that a target file must exist on the real filesystem at the same relative path. Note that this vulnerability only allows modification of file attributes; file contents cannot be read or altered through this attack vector.</p><p>If the SSH daemon runs as <tt>root</tt>, this enables direct privilege escalation: an attacker can set the setuid bit on any binary, change ownership of sensitive files, or make system configuration world-writable.</p><p>This vulnerability is associated with program files <tt>lib/ssh/src/ssh_sftpd.erl</tt> and program routines <tt>ssh_sftpd:do_open/4</tt> and <tt>ssh_sftpd:handle_op/4</tt>.</p><p>This issue affects OTP from OTP 17.0 until OTP 28.4.3, 27.3.4.11, and 26.2.5.20 corresponding to <tt>ssh</tt> from 3.01 until 5.5.3, 5.2.11.7, and 5.1.4.15.</p>"
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}
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],
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"value": "Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') vulnerability in Erlang OTP ssh (ssh_sftpd module) allows an authenticated SFTP user to modify file attributes outside the configured chroot directory.\n\nThe SFTP daemon (ssh_sftpd) stores the raw, user-supplied path in file handles instead of the chroot-resolved path. When SSH_FXP_FSETSTAT is issued on such a handle, file attributes (permissions, ownership, timestamps) are modified on the real filesystem path, bypassing the root directory boundary entirely.\n\nAny authenticated SFTP user on a server configured with the root option can modify file attributes of files outside the intended chroot boundary. The prerequisite is that a target file must exist on the real filesystem at the same relative path. Note that this vulnerability only allows modification of file attributes; file contents cannot be read or altered through this attack vector.\n\nIf the SSH daemon runs as root, this enables direct privilege escalation: an attacker can set the setuid bit on any binary, change ownership of sensitive files, or make system configuration world-writable.\n\nThis vulnerability is associated with program files lib/ssh/src/ssh_sftpd.erl and program routines ssh_sftpd:do_open/4 and ssh_sftpd:handle_op/4.\n\nThis issue affects OTP from OTP 17.0 until OTP 28.4.3, 27.3.4.11, and 26.2.5.20 corresponding to ssh from 3.01 until 5.5.3, 5.2.11.7, and 5.1.4.15."
"title": "SFTP chroot bypass via path traversal in SSH_FXP_FSETSTAT",
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"workarounds": [
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{
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"lang": "en",
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"supportingMedia": [
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{
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"base64": false,
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"type": "text/html",
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"value": "<ul><li>Do not use the <tt>root</tt> option in <tt>ssh_sftpd:subsystem_spec/1</tt>, and instead rely on OS-level chroot or container isolation to confine SFTP users.</li><li>Ensure the Erlang VM is not running as a privileged OS user. Running the VM as an unprivileged user limits the impact of this vulnerability, since attribute modifications are constrained by that user's OS-level permissions.</li></ul>"
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}
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],
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"value": "* Do not use the root option in ssh_sftpd:subsystem_spec/1, and instead rely on OS-level chroot or container isolation to confine SFTP users.\n* Ensure the Erlang VM is not running as a privileged OS user. Running the VM as an unprivileged user limits the impact of this vulnerability, since attribute modifications are constrained by that user's OS-level permissions."
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