Originally written by blakkheim on 03/18/2016. Last updated on 07/07/2019.
This page is intended to list the major changes I used to make to a vanilla install of FreeBSD. Some are preferences, but the majority are for security. It only covers some basic high level changes that a sysadmin can easily make to a running system. It does not go in depth about changing FreeBSD's more serious low-level problems that require code changes.
It could also be considered a commentary piece on the state of security in FreeBSD's development ecosystem, highlighting their strong resistance to change and unwillingness to replace old cruft with modern alternatives. Most of that is in the closing section towards the end.
Their security page says the following:
FreeBSD takes security very seriously and its developers are constantly working on making the operating system as secure as possible.
But is that really true? Let's find out.
Table of Contents
It is my belief that quite a few poor decisions have been made in this area. As a primary example, they insisted on maintaining the HPN-SSH patchset and enabling it by default for quite a long time.
You might say "Well OK, but what's actually wrong with those patches?"
A few years ago, OpenSSH increased the channel limits enough to support a cross-country gigabit connection without slowdown. For most users, this means that the HPN patches are an unnecessary complexity with little to no benefit. In addition to that, they would frequently hold FreeBSD back from updating their version of OpenSSH because of HPN backporting and manual refactoring of the patchset.
Support for tcp_wrappers was abandoned long ago in OpenSSH upstream, but FreeBSD still patched it back in and enabled it for everyone.
The same was true for weak DSA host keys, which they switched back on for compatibility with older clients.
FreeBSD also re-enabled insecure encryption ciphers in their build after they've been disabled upstream, with backward compatibility apparently being more important to them than the security of their users.
If we don't deprecate insecure options bit by bit somewhere in the ecosystem, we end up with a situation like OpenSSL. Pressure has to be applied somewhere. One can be part of that team, or one can play against them.
FreeBSD is the team trying to increase the risk.
They've made local changes to their OpenSSH build and its default config files that left their users vulnerable when other platforms were unaffected. Here's a (possibly incomplete) list of examples:
And the PAM issues in these two:
A list of FreeBSD's modifications to both the code and config files can be seen here for the base system (possibly outdated/unmaintained) and here for the ports version.
Thankfully, as hinted above, it's fairly easy to install OpenSSH from ports with all the FreeBSDisms removed. Their often-outdated openssh-portable port has a convenient set of options you can toggle. As of the time I'm writing this, the list is as follows:
[ ] BSM OpenBSM Auditing [X] HPN HPN-SSH patch [ ] KERB_GSSAPI Kerberos/GSSAPI patch (req: GSSAPI) [X] LDNS SSHFP/LDNS support [X] LIBEDIT Command line editing via libedit [ ] NONECIPHER NONE Cipher support [ ] OVERWRITE_BASE EOL, No longer supported [X] PAM Pluggable authentication module support [ ] SCTP SCTP support [X] TCP_WRAPPERS tcp_wrappers support [ ] X509 x509 certificate patch ( ) MIT MIT Kerberos (security/krb5) ( ) HEIMDAL Heimdal Kerberos (security/heimdal) ( ) HEIMDAL_BASE Heimdal Kerberos (base)
An X means it's on by default for users of the project's binary pkg repo and ports/poudriere users that don't explicitly change their build options. (More on all of those later.)
Besides the modifications mentioned above, two other patches in particular have been popular with FreeBSD users:
Threaded AES-CTR, as the name might imply, introduces threads to the code. OpenSSH devs have publicly said threads are too risky and won't be added. What's more, it's largely obsoleted by AES-NI in modern CPUs and the fact that ChaCha20-Poly1305 (the current default cipher) is even faster when taking the Message Authentication Code into consideration.
The NONE cipher is somewhat of a misfeature, removing the encryption bits and only keeping the data integrity. It allows users to accidentally shoot themselves in the foot pretty easily. The trade-off in performance isn't really worth it either, as the bottlenecks one might experience have a lot more to do with the MAC than the actual encryption.
I recommend disabling all of the port options. The majority of users don't need the extra risk that any of these non-standard patches introduce.
As for the /usr/local/etc/ssh/sshd_config file, I would recommend enabling only modern crypto. However, cryptography is a very complicated and important topic, so you would be better served to research each algorithm and come to your own conclusions instead of just taking my word for it. Thankfully upstream OpenSSH cares about security and continues to remove old, broken algorithms. FreeBSD can't keep patching them back in and maintaining their backports - it's simply too much work.
This isn't meant to be an entire SSH tutorial, but consider changing your default port to something other than 22 if you want less spam in your logs, set up public keys and disable password authentication... the usual stuff.
The following config lines are just to revert FreeBSD's local changes that introduce new risks:
ChallengeResponseAuthentication no UsePAM no VersionAddendum none # Prevent some OS information from being # leaked by your sshd, another one of # FreeBSD's "enhancements" in both the # base system and ports version. X11Forwarding no
In addition to improved security, using the port of OpenSSH allows you to upgrade to newer versions much faster than waiting for a new release of the base system. Note that you may need further configuration changes if using the bundled OpenSSH, as its compile-time options aren't as easily fixable.
I'd like to share a quote from one of the earliest security advisories FreeBSD ever published:
The sendmail mail transfer agent has a rather poor reputation for security related problems. FreeBSD ships a version of sendmail that has all known security problems fixed, but this doesn't mean there won't be more found in the future.And it turns out whoever wrote that back in 1996 wasn't wrong.
Even with Sendmail's atrocious reputation, FreeBSD has kept it around and left it on by default for all their users.
I think most users will agree that this program is mostly just a bother, and it shouldn't be in the base system at all if you ask me. I stop all the related services because it makes startup slower and I'd like as few things running in the background as possible. The lines to disable Sendmail will be in the rc.conf section towards the end.
If you actually run a mail server, there are better options like Postfix or OpenSMTPD. If you only need to send mail through a third party provider like Gmail, msmtp is a another lightweight alternative. All three are in ports.
I don't know anything about IPFilter, nor do I know anyone that uses it, so we'll pretend it doesn't exist. IPFW is the native firewall. It was written by FreeBSD for FreeBSD. PF is the OpenBSD firewall. It was ported from OpenBSD to FreeBSD. Both are fine choices, and it ultimately comes down to your preference between the two. Since I'm more familiar with PF, that's what I use. Unfortunately, the version of PF included with FreeBSD hasn't been synced with upstream since 2009. Do you want such a critical component of your OS (or network device) left largely unmaintained? I don't.
Check the documentation for whichever firewall you decide to use for proper configuration instructions.
There are pros and cons to each.
However, more security concerns arise...
Both the ports system and pkg will do a lot of things as root where it's not needed at all. I brought this up to a member of the ports security team and he simply shrugged it off. Just because portsnap checks the snapshots it fetches against a public key, he figured there was nothing to worry about. I have to question their credibility sometimes.
It's true that verifying the files it fetches would indeed be a good countermeasure, if that was done before the more dangerous operations... but it wasn't. The data integrity check was done very late in the process, giving plenty of opportunity for exploits against the other tools called by the shell script, all running as root and taking untrusted input from the internet. Both portsnap and freebsd-update have a serious design flaw here that could be easily fixed. Perhaps they have the utmost confidence in the tools being bug-free, but I try to be a bit more realistic.
And it turns out I was right, detailed extensively here. The short version is basically "anyone using these tools can be remotely compromised at the root level."
Similar issues were brought up on their mailing lists, though nothing ever came of that discussion either.
Despite the issues being brought up on their lists in April 2014, despite public exploits being published in May 2016, and despite multiple big news sites picking up the story, they were all left unfixed until October 2016. The FreeBSD security team left all users vulnerable to these exploits for a very long time. This goes well beyond just insecure default settings.
But back to ports and pkg, where similar design flaws will probably never be fixed.
There's more risk involved than just letting root go out to the internet to download files. Here's a summary of what happens in the process of building ports:
1. Fetch and update the ports tree (a collection of makefiles and patches)
2. Fetch the software's source code
3. Verify the checksum of the file(s)
4. Extract the source tarball
5. Run the configure script, apply local patches, and build the application
6. Create a package from the built files
7. Install the package to your system (if desired)
So how many of these actually need to be done as root? Only the last one. And how many of these are done as root by default in FreeBSD? All of them.
PID USERNAME THR PRI NICE SIZE RES STATE C TIME WCPU COMMAND 84266 root 1 52 0 36272K 8056K wait 0 0:00 0.68% cc 84191 root 1 52 0 9116K 1332K wait 0 0:00 0.29% make 84267 root 1 47 0 36416K 20484K zio->i 1 0:00 0.00% cc
Maybe people don't realize the risk of actually building all these third party tools with root privileges. Have you read every line of those 25,000+ configure scripts? I've seen some configure scripts running ping to phone home and all kinds of weird stuff. Since everything runs as root, all it takes is one malicious command tucked away in a build script somewhere to completely compromise the host if you use ports in its default configuration.
This is made even worse by the negligence of some port maintainers, as was the case in the cryptographic bypass and MITM-based compromise against certain ports.
Surprisingly, FreeBSD does have some support for doing package builds as a non-root user. Though I'm told staging is integrated into all their ports now, the default is still to do everything as root. Why?
To work around this issue, I tried manually introducing some privsep in the build process on my machine with a "_ports" user. You'd need to chown a few directories or make them writable by this user. Many changes were needed in the /etc/make.conf file, and it appears that it's really just not designed to be done this way, so I'd call it more of an experiment than a solution. Why is all this needed? It's like things were designed to be as troublesome to secure as possible so no one ever tries it. Hey, works as intended if so.
The poudriere tool uses FreeBSD's jail system for some filesystem isolation during the process, so it's a little safer than using ports in this regard. However, the distfiles are still fetched as root, the portsnap/svn commands are run as root, etc. That's on the host system, by the way, not jailed. All these tasks are trivial to isolate with different users, but poudriere doesn't do that. The only operation that poudriere does as an unprivileged user is the compiling, and that change took years of pressure to make.
The pkg tool itself also runs everything as root, from fetching and verifying the packages to untarring them and registering their installation.
PID USERNAME THR PRI NICE SIZE RES STATE C TIME WCPU COMMAND 84554 root 1 22 0 42996K 7452K select 1 0:00 0.59% pkg
Just for comparison, look at the security history of Debian's pkg equivalent. Different codebases, sure, but it shows that these types of programs can be difficult to secure properly. Why let a trivial bug turn into a privilege escalation nightmare? Actually, for FreeBSD, I guess there's no "escalation" since it's already running as root the whole time...
FreeBSD's binary packages are also fetched over plaintext HTTP by default, even though the main mirror site supports HTTPS. This is likely because their base system doesn't include any root certificate bundle. They can make room for Sendmail, but not that.
The "but packages are signed!" defense I've gotten from some users really demonstrates a lack of understanding of what's actually going on when you run that pkg command.
A side note: OpenBSD's dpb tool (similar to poudriere) really got all this stuff right, even going as far as to use separate users to download and build the software, and recommending to disallow the build user from accessing the internet at all. It's cool stuff, especially when combined with pledge to restrict the system calls available to each sub-process. It would be nice to see more use of FreeBSD's Capsicum here, wouldn't it?
The code was written mainly by time geeks and scientists instead of people who actually run network-facing services. Obviously I want to keep my clock synced to the correct time, so what do I do here? Luckily, there are a number of alternative NTP daemons to choose from.
One FreeBSD committer is/was working on an NTP implementation called ntimed. I haven't tried it myself. Can't be any worse than what FreeBSD ships now, though.
Another option, the one I use, is called OpenNTPD. Based on the name, see if you can guess where it originates. A simple /usr/local/etc/ntp.conf may look something like this:
constraint from "https://www.freebsd.org" servers pool.ntp.org
Note that the constraints option is not available for FreeBSD's default package. If you want that additional security benefit, you need to use LibreSSL instead of OpenSSL. Details on that later.
Much like the firewall section, this is up to your personal preference. There are trade-offs for both. OpenNTPD has an excellent security track record and a simple config syntax, but ntimed will likely give you better microsecond precision. Whichever you choose, just don't use the base one.
hw.kbd.keymap_restrict_change=4 kern.ipc.shm_use_phys=1 net.inet.ip.check_interface=1 net.inet.ip.process_options=0 # Enable if you need IGMP or multicast. net.inet.ip.random_id=1 net.inet.ip.redirect=0 net.inet.tcp.cc.algorithm=cubic net.inet.icmp.drop_redirect=1 net.inet.tcp.drop_synfin=1 net.inet.sctp.blackhole=2 net.inet.tcp.blackhole=2 net.inet.udp.blackhole=1 # Note the blackhole options can sometimes # make debugging network issues more difficult. net.inet.tcp.icmp_may_rst=0 security.bsd.hardlink_check_gid=1 # These two options will break poudriere's security.bsd.hardlink_check_uid=1 # compiling privsep. security.bsd.see_other_gids=0 security.bsd.see_other_uids=0 security.bsd.stack_guard_page=1 security.bsd.unprivileged_proc_debug=0 security.bsd.unprivileged_read_msgbuf=0
The following descriptions were taken from "sysctl -d" output with some minor grammar fixes.
hw.kbd.keymap_restrict_change - Restrict ability to change keymap
kern.ipc.shm_use_phys - Enable/Disable locking of shared memory pages in core
net.inet.icmp.drop_redirect - Ignore ICMP redirects
net.inet.ip.check_interface - Verify packet arrives on correct interface
net.inet.ip.process_options - Enable IP options processing ([LS]SRR, RR, TS)
net.inet.ip.random_id - Assign random ip_id values (FreeBSD does not randomize IP IDs by default.)
net.inet.ip.redirect - Enable sending IP redirects
net.inet.sctp.blackhole - Enable SCTP blackholing (SCTP being enabled in the kernel is another horrible default. Long history of security problems. Highly recommend removing it from your kernel.)
net.inet.tcp.blackhole - Do not send RST on segments to closed ports
net.inet.tcp.cc.algorithm - Default TCP congestion control algorithm (FreeBSD uses newreno by default, which is severely outdated and often results in poor upload speeds for LFNs.)
net.inet.tcp.drop_synfin - Drop TCP packets with SYN+FIN set
net.inet.tcp.icmp_may_rst - Certain ICMP unreachable messages may abort connections in SYN_SENT
net.inet.udp.blackhole - Do not send port unreachables for refused connects
security.bsd.hardlink_check_gid - Unprivileged processes cannot create hard links to files owned by other groups
security.bsd.hardlink_check_uid - Unprivileged processes cannot create hard links to files owned by other users
security.bsd.see_other_gids - Unprivileged processes may see subjects/objects with different real gid
security.bsd.see_other_uids - Unprivileged processes may see subjects/objects with different real uid
security.bsd.stack_guard_page - Insert stack guard page ahead of the growable segments (Also see The Stack Clash for a report on how poorly this was implemented.)
security.bsd.unprivileged_proc_debug - Unprivileged processes may use process debugging facilities
security.bsd.unprivileged_read_msgbuf - Unprivileged processes may read the kernel message buffer
Have a look at the /etc/defaults/periodic.conf file. It shows which scripts from the base system are run by default when periodic is called from cron. In a standard configuration, all periodic scripts can be seen in either /etc/periodic (for base daemons) or /usr/local/etc/periodic (for ports). When you install a port or package, it may also add new periodic scripts and even enable them by default - something to be aware of.
For reference, this is the /etc/periodic.conf that I use to disable much of the background activity.
daily_backup_aliases_enable="NO" daily_backup_pkg_enable="NO" daily_backup_pkgdb_enable="NO" daily_clean_preserve_enable="NO" daily_clean_rwho_enable="NO" daily_status_pkg_changes_enable="NO" daily_status_security_chkmounts_enable="NO" daily_status_security_chkportsum_enable="NO" daily_status_security_chksetuid_enable="NO" daily_status_security_enable="NO" daily_status_security_ipfdenied_enable="NO" daily_status_security_ipfwdenied_enable="NO" daily_status_security_neggrpperm_enable="NO" daily_status_security_pfdenied_enable="NO" daily_status_security_pkg_checksum_enable="NO" daily_status_security_pkgaudit_enable="NO" monthly_accounting_enable="NO" monthly_statistics_enable="NO" monthly_statistics_report_devices="NO" monthly_status_security_enable="NO" weekly_locate_enable="NO" weekly_noid_enable="NO" weekly_status_pkg_enable="NO" weekly_status_pkg_enable="NO" weekly_status_security_enable="NO" weekly_whatis_enable="NO"
That list may not be what everyone wants, and that's ok. Since your needs will dictate which scripts you want running, I'll only suggest disabling one in particular...
I most certainly don't want pkg (running as root, remember?) going out to the internet every night to fetch a list of vulnerable ports. Who thought this was safe?
Being alerted to vulnerabilities in your installed packages is nice, but there's simply no need to be doing this operation as root. The dangerous combination of laziness and poor software design is quite prevalent here.
Similar to the NTP list, I would expect many more of these to come out. Also note that many of these advisories contain multiple vulnerabilities.
FreeBSD releases have even been delayed due to OpenSSL security bugs on more than one occasion.
And what about when FreeBSD leaves your version vulnerable for months at a time or more?
We're dealing with highly insecure software, maintained by a largely-inactive "security team," and it's an obvious recipe for disaster.
So how can we make things better? In FreeBSD, your SSL library choices essentially come down to these three:
DEFAULT_VERSIONS+=ssl=libressl-devel # or "libressl" for older stable version
Time has shown that switching to LibreSSL will cut down the number of vulnerabilities you have to deal with by a considerable margin, as well as the average severity of them. In contrast to FreeBSD's bundled version of OpenSSL, you'll also actually get the security fixes when a new version is released, assuming your ports are kept up to date.
Am I the only one who sees a problem here?
Here's an example /etc/fstab line for a standard swap partition:
# Device Mountpoint FStype Options Dump Pass# /dev/ada0p3 none swap sw 0 0
Now here's the same thing with the swap automatically encrypted:
# Device Mountpoint FStype Options Dump Pass# /dev/ada0p3.eli none swap sw 0 0
All you need to do is add ".eli" to the device name. A one-time key will be generated and destroyed when swap is unmounted, so the swap contents should be unrecoverable. If you had unencrypted swap previously, consider using dd to write random data over it before encrypting.
These are the relevant lines in my /etc/rc.conf file:
clear_tmp_enable="YES" microcode_update_enable="YES" ntpd_enable="NO" openntpd_enable="YES" openntpd_flags="-s" openssh_enable="YES" pf_enable="YES" sendmail_enable="NO" sendmail_msp_queue_enable="NO" sendmail_outbound_enable="NO" sendmail_submit_enable="NO" sshd_enable="NO" syslogd_flags="-ss"
Make sure you understand the difference between sshd_enable and openssh_enable if you're doing this on a remote machine.
cc_cubic_load="YES" hw.mds_disable=3 kern.randompid=1 kern.random.fortuna.minpoolsize=128 machdep.hyperthreading_allowed="0"
FreeBSD does not randomize process IDs by default, so we enable that. Also increase the minimum entropy pool size necessary to cause a reseed. The default is a bit low for my taste. The CUBIC TCP congestion control algorithm requires a kernel module to be loaded or it won't work. The default "newreno" algorithm is very old and not suitable for modern networks. Intel's hyperthreading technology (also known as SMT, Simultaneous MultiThreading) has proven itself to be insecure, so it should be disabled here. Adding that line is also harmless if your CPU does not have SMT. Finally, FreeBSD thought it would be a good idea to fix the Intel MDS vulnerability but leave the fix turned off by default, so it must be enabled if you are using an affected CPU.
The resistance from the security team to phase out legacy options makes me wonder if they should be called The Backwards Compatibility Team instead.
The FreeBSD Security Officer's mission is to protect the FreeBSD user community by keeping the community informed of bugs, exploits, popular attacks, and other risks; by acting as a liaison on behalf of the FreeBSD Project with external organizations regarding sensitive, non-public security issues; and by promoting the distribution of information needed to safely run FreeBSD systems, such as system administration and programming tips.(From their security charter page.)
In my view, the security team of today seems to be doing the exact opposite of a number of those tasks. I'd really like to see some things re-evaluated for the safety of their userbase. Fix the problems; don't ship poor defaults and expect the users to clean them up.
That said, FreeBSD's history of security problems goes far beyond just poor default settings in the OS. There's a severe lack of transparency in the security team's disclosure policy too, which leaves their users vulnerable to attack for long periods of time. Many known vulnerabilities are left unpatched in FreeBSD for months on end.
Oh, did I say months? I meant years.
It seems FreeBSD's own developers are realizing how much of a circus it is.
That's curious to me, considering how few of their developers actually run the -CURRENT branch. Did a big compiler update leave a lot of ports broken? Yes, sometimes for over three months, but the port maintainers just delete the reports since they don't use it.
The extra legwork of maintaining so many supported branches means that none of them ever get the developers' full attention, and you're bound to run into problems in one branch that were fixed (or never happened) in another.
On a similar note, it's increasingly common for security fixes to go in without any mention of security at all. No advisory published. Nothing. If you use -RELEASE, you simply do not get the fix. You're not even told it exists.
This problem is much worse in ports, where a simple "update to version xyz" commit log often hides substantial security fixes... which then don't get merged back to the quarterly branch... which is the default on new installs. Great.
But maybe that's less of an issue when the security fixes never get committed in the first place.
FreeBSD lacks any sort of modern exploit mitigation techniques, only getting basic ASLR (technically more along the lines of ASR, without stack/shared page randomization, making it nearly useless from a security perspective) in their development branch in 2019. It's disabled by default, of course.
For comparison, OpenBSD introduced ASLR in 2003, Linux in 2005, and Windows in 2007.
A FreeBSD developer posted an experimental early version of the ASLR patch in 2016, but explains that it is to be intentionally weak (sorry, I meant "non-aggressive") by default.
Other basic mitigation techniques like W^X don't seem to be planned as far as I can tell. This means that, as far as exploit mitigations go, FreeBSD is still absolutely stuck in the stone ages.
Network-facing services running on FreeBSD are particularly vulnerable to attack as a result of this.
Even local systems are comparatively vulnerable, thanks to the ever-present "performance first, security last" mindset.
Log Message: Add a new "untrusted" option to the mount command. Its purpose is to notify the kernel that the file system is untrusted and it should use more extensive checks on the file-system's metadata before using it. This option is intended to be used when mounting file systems from untrusted media such as USB memory sticks or other externally-provided media.
I see an obvious logic error in that commit... and it's not in the code.
FreeBSD's malloc (jemalloc) is very forgiving of buggy/hostile code compared to something like otto malloc.
FreeBSD's net installer fetches the unsigned OS files as root over plaintext (FTP/HTTP) protocols.
It took FreeBSD four years to switch their arc4random algorithm from RC4 (known to be broken) to ChaCha20, even when multiple patches were presented to fix it.
There's often very little review (or none at all) of the crypto code and security fixes in general.
This has even resulted in catastrophic failures like the RNG being broken for months without anyone noticing.
Or the time when all high quality entropy sources were accidentally disabled.
Or the time when kernel code preventing shell injection was removed without any review or approval of the change.
It seems that anyone with SVN access can commit whatever they want (or, more often, what their parent company wants) without any communication with other FreeBSD developers or any code review. This "commit-then-discuss" culture usually leads to long arguments on the mailing lists and glaring security problems, all of which could be prevented if some review had taken place.
Remember that line from the beginning of this page?
FreeBSD takes security very seriously and its developers are constantly working on making the operating system as secure as possible.I think it's safe to say that's a big lie.
The FreeBSD Foundation gets over a million dollars in donations every year, so you might be wondering why the project can't get any of this stuff right. Well, it seems they've got other plans for how to use your money.
In conclusion, I can't recommend FreeBSD for any task where security matters. The OS is about as secure as a Linux box from the 1990s, and the developers are more interested in keeping corporate donors happy than making a good operating system.
Five months after this document was published, FreeBSD introduced minimal privilege separation into their pkg tool. Though reverted just one day after being committed, pkg privsep was then revisited two months later and once again reverted in December. If you're keeping track of all the flip-flops, that means it's still going out to the internet as root.
Ten months after this document was published, FreeBSD disabled the HPN patchset in their bundled version of OpenSSH.
One year after this document was published, FreeBSD enabled some of the sysctl recommendations by default in their development branch's installer. It was reverted just one month later. Due to FreeBSD's release schedule, it wouldn't have reached the majority of their users for quite some time anyway. Users who upgrade between releases (rather than reinstalling) wouldn't have seen those options at all. When it was introduced, multiple developers on the mailing list were in favor of reverting the change. With a development community like that, it's not hard to see why little progress is ever made.
Nearly two years after this document was published, FreeBSD disabled the HPN patchset in the ports version of OpenSSH. Removal of HPN from both base and ports appears to be due to build failures rather than security considerations.
Nearly two years after this document was published, FreeBSD switched the poudriere tool's default build user from root to an unprivileged one, but left the distfile fetching operation (and others) running as root.
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