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13 <H2 align="center">Rsync Security Advisories</H2>
15 <p><a name="s3_1_3"></a><hr>
16 <h3>File-list validation in 3.1.3</h3>
17 <i class=date>January 28st, 2018</i>
19 <p>If you are using a version of rsync older than 3.1.3 as a client and
20 receiving xattrs from an rsync server that you might not fully trust, a
21 malicious (modified) server could send a non-null-terminated xattr name to
22 overflow the xattr read buffer.
24 <p>If you are running a writable rsync daemon older than 3.1.3, you should add
25 a rule "refuse options = protect-args" if you don't fully trust the users who
26 are sending you files.
28 <p><a name="s3_1_2"></a><hr>
29 <h3>File-list validation in 3.1.2</h3>
30 <i class=date>December 21st, 2015</i>
32 <p>If you're using a version of rsync older than 3.1.2 as a client and
33 receiving files from an rsync server that you might not fully trust, this
34 version adds extra checking to the file list to prevent the sender from
35 tweaking the paths and/or the transfer requests in a way that could cause
36 a file to be received outside the transfer destination.
38 <p><a name="s3_0_2"></a><hr>
39 <h3>Xattr security fix in 3.0.2</h3>
40 <i class=date>April 8th, 2008</i>
42 <p>If you're using a version of rsync from 2.6.9 to 3.0.1 that has extended
43 attribute (xattr) support enabled, you should upgrade to 3.0.2 to avoid a
44 potential buffer overflow problem. All 3.x versions have the potential to
45 support xattrs (depending on OS availability and the configure options used),
46 but version 2.6.9 had to be patched for this support. You can run the command
47 "rsync --version" and look for the string "xattrs" (as long as it is not
48 "no xattrs") to see if your rsync is affected.
50 <p>For those running affected versions, there is
51 <a href="https://download.samba.org/pub/rsync/security/rsync-3.0.1-xattr-alloc.diff">a
52 patch with the fix available</a>.
54 <p>Those running a writable rsync daemon can opt to refuse the "xattrs" option
55 as a way to avoid the problem without an upgrade:
57 <blockquote><pre>refuse options = xattrs</pre></blockquote>
59 <p>(If you already refuse options, be sure to append "xattrs" to your existing
60 config parameter rather than adding another refuse directive.)
62 <p><a name="s3_0_0"></a><hr>
63 <h3>Daemon security fixes in 3.0.0 (with patches for 2.6.9)</h3>
64 <i class=date>First published on November 28th, 2007;<br>
65 Updated on December 16th, 2007;<br>
66 Item 3 added on February 15th, 2008</i>
68 <p>Three security advisories affect people who run a <b>writable</b> rsync
69 daemon: The first affects only those with "use chroot = no" (which is not a
70 very safe combination in general), the second affects a daemon that has
71 daemon-excluded files that are being hidden in a module's hierarchy, and
72 the third affects only those with "use chroot = yes".
73 Included are simple config-change suggestions that should help you to
74 avoid the security issues and patches that make things safer.
75 These advisories affect all rsync versions.
77 <h4>1. Daemon advisory for "use chroot = no"</h4>
79 <p>If you are running a writable rsync daemon with "use chroot = no", there
80 is at least one way for someone to trick rsync into creating a symlink
81 that points outside of the module's hierarchy.
83 <p>This means that if you are allowing access from users who you don't
84 trust, that you should either figure out a way to turn on "use chroot",
85 or configure the daemon to refuse the "links" option (see "refuse
86 options" in the rsyncd.conf manpage) which will disable the ability of
87 the rsync module to receive symlinks. After doing so, you should also
88 check that any existing symlinks in the daemon hierarchy are safe.
90 <p>Starting with the 3.0.0-pre6 release, there is a new daemon parameter
91 available: "munge symlinks". This allows an rsync daemon to accept
92 symlinks and return them intact (with even a leading slash still there,
93 which is new for a non-chroot daemon), but will not allow the symlinks
94 to be used while they are in the daemon's hierarchy.
98 <a href="https://download.samba.org/pub/rsync/security/rsync-2.6.9-munge-symlinks.diff">a
99 patch for 2.6.9 to implement this parameter</a>.
101 <p>Any admin applying that patch should read the "munge symlinks" section
102 of the modified rsyncd.conf manpage for more information. You can also
103 read about this parameter in the
104 <a href="https://download.samba.org/pub/rsync/rsyncd.conf.html">rsyncd.conf
105 manpage from a 3.x version</a>.
107 <h4>2. Daemon advisory for daemon excludes</h4>
109 <p>If you are running a writable rsync daemon that is using one of the
110 "exclude", "exclude from", or "filter" parameters in the rsyncd.conf file
111 to hide data from your users, you should be aware that there are tricks
112 that a user can play with symlinks and/or certain options that can allow
113 a user that knows the name of a hidden file to access it or overwrite it
114 (if file permissions allow that).
116 <p>You can avoid the symlink problem using the suggestions in the advisory
119 <p>When a daemon has "use chroot = no" set , there was some buggy
120 exclude-checking for these options: <code>--compare-dest</code>,
121 <code>--link-dest</code>, <code>--copy-dest</code>, <code>--partial-dir</code>,
122 <code>--backup-dir</code>, <code>--temp-dir</code>, and
123 <code>--files-from</code>. These are fixed in the 3.0.0pre7 release. For
124 those running 2.6.9, there is <a
125 href="https://download.samba.org/pub/rsync/security/rsync-2.6.9-daemon-exclude.diff">a patch for
126 2.6.9</a> to fix these checks.
128 <p>Some of the above options can still cause problems if an excluded
129 sub-directory or filename is inside the option's directory hierarchy and the
130 names of a transferred file clashes with it. The affected options are the
131 various <code>--*-dest</code> options (of which only <code>--link-dest</code>
132 is particularly worrisome),
133 <code>--backup-dir</code>, and <code>--partial-dir</code>.
135 <p>You can avoid these sub-path problems by putting the following "refuse
136 options" setting into your rsyncd.conf file:
138 <blockquote><pre>refuse options = link-dest backup-dir partial-dir</pre></blockquote>
140 <p>Those who aren't using an rsync with the latest exclude fixes may want to add
141 some of the other affected options as well.
143 <h4>3. Daemon advisory for "use chroot = yes"</h4>
145 <p>If you are running a writable rsync daemon with "use chroot = yes", you
146 should take care that users cannot upload their own library files and attempt
149 <p>Beginning with rsync 3.0.0pre10, you can specify an inside-chroot path that
150 makes the top of the transfer a subdirectory inside the chroot area, and that
151 automatically makes library loading occur outside the transfer area (assuming
152 you didn't pick an unwise subdirectory name for the transfer area and you
153 don't have symlinks that point outside the transfer area).
155 <p>If that solution is not good for you, the easiest way to protect your daemon
156 is to create some appropriate directories in the top of your module's path
157 hierarchy, such as "/etc", "/lib", and "/usr" (and any other top-level dirs
158 that might be in the load path), chown those directories to some other user
159 than the one that the module runs as (so that rsync will not be able to write
160 files there, assuming that it is not run as root), and then hide the dirs using
161 an exclude directive (either add a new one or extend your existing one):
163 <blockquote><pre>exclude = /etc /lib /usr</pre></blockquote>
165 <p>Doing all that will assure you that no user will be able to use rsync to
166 upload a library that can be potentially loaded while rsync is attempting to
167 perform an action, such as translating a username. You can feel free to put
168 trusted libraries that you want rsync to access in the protected hierarchies,
171 <p>Also available in rsync 3.0.0pre10 is a new daemon parameter that allows you
172 to avoid the accessing of user/group-name translation libraries by a chrooted
173 rsync: the "numeric ids" daemon parameter lets you turn on a forced
174 numeric-only mode. The default for a chroot module is to enable this
175 parameter, while the default for a non-chroot module is to disable it.
177 <p>For those running 2.6.9, there is <a
178 href="https://download.samba.org/pub/rsync/security/rsync-2.6.9-daemon-ids.diff">a patch for
179 2.6.9</a> to add the "numeric ids" daemon config parameter. (The patch will
180 only apply cleanly if you've already applied the munge-symlinks diff mentioned
183 <p><a name="s2_6_8"></a><hr>
184 <h3>Xattr security fix in 2.6.8</h3>
185 <i class=date>April 22th, 2006</i>
187 <p>If you're using a version of rsync prior to 2.6.8 that was patched to
188 include extended attribute (xattr) support, you should upgrade to 2.6.8 or
189 later to avoid a potential buffer overflow problem.
191 <p><a name="s2_6_6"></a><hr>
192 <h3>Zlib security fix in 2.6.6</h3>
193 <i class=date>July 28th, 2005</i>
195 <p>If you're using a version of rsync prior to 2.6.6, there is a potential
196 null-pointer security bug in the zlib code. You can avoid its affect in an
197 rsync daemon situation by configuring rsync to refuse the "compress" option.
199 <p><a name="s2_6_3"></a><hr>
200 <h3>Daemon path-sanitizing fix in 2.6.3</h3>
201 <i class=date>August 12th, 2004</i>
203 <p>There is a path-sanitizing bug that affects daemon-mode in
204 rsync versions prior to 2.6.3, but only if "use chroot" is disabled. It
205 does <b>not</b> affect the normal send/receive filenames that specify what
206 files should be transferred (this is because these names happen to get
207 sanitized twice, and thus the second call removes any lingering leading
208 slash(es) that the first call left behind). It does affect certain
209 option paths that cause auxiliary files to be read or written.
211 <p>One potential fix that doesn't require recompiling rsync is to set
212 "use chroot = true" for all the modules in the rsyncd.conf file.
214 <p><a name="s2_6_1"></a><hr>
215 <h3>Daemon security fix in 2.6.1</h3>
216 <i class=date>April 26th, 2004</i>
218 <p>There is a security problem in all versions prior to 2.6.1 that affects only
219 people running a read/write daemon with "use chroot" disabled. If the user privs
220 of a module in the daemon config is anything above "nobody", you are at risk
221 of someone crafting an attack that could write a file outside of the module's
222 "path" setting (where all its files should be stored). Please either enable
223 chroot or upgrade to 2.6.1. People not running a daemon, running a read-only
224 daemon, or running a chrooted daemon are totally unaffected.
226 <p><a name="s2_5_7"></a><hr>
227 <h3>Memory overflow fix in 2.5.7</h3>
228 <i class=date>December 4th, 2003</i>
230 <p>Rsync versions prior to 2.5.7 contain a heap overflow vulnerability that
231 could be used to remotely run arbitrary code, but this only affects the use of
232 rsync as an "rsync daemon" (where rsync handles incoming socket connections,
233 typically on port 873).
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