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[nse]: ssh2-enum-algos: Add dropbear server support #1460

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@scottellis scottellis commented Feb 5, 2019

Dropbear servers send key exchange algorithms as part of the first
transfer along with the banner.

There is no need to send a separate kex-init request and the server
ignores the request anyway resulting in no output from the script.

Dropbear servers send key exchange algorithms as part of the first
transfer along with the banner.

There is no need to send a separate kex-init request and the server
ignores the request anyway resulting in no output from the script.
@scottellis
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@scottellis scottellis commented Feb 5, 2019

Tested with several Dropbear versions

  • dropbear-2014.63
  • dropbear-2015.68
  • dropbear-2016.74
  • dropbear-2017-75
  • dropbear-2018.76

Some sample runs

A wifi AP running asuswrt-merlin

# nmap -p22 -n -sV --script ssh2-enum-algos 192.168.10.13
Starting Nmap 7.70 ( https://nmap.org ) at 2019-02-05 10:06 EST
Nmap scan report for 192.168.10.13
Host is up (0.00076s latency).

PORT   STATE SERVICE VERSION
22/tcp open  ssh     Dropbear sshd 2018.76 (protocol 2.0)
| ssh2-enum-algos:
|   kex_algorithms: (8)
|       curve25519-sha256
|       curve25519-sha256@libssh.org
|       ecdh-sha2-nistp521
|       ecdh-sha2-nistp384
|       ecdh-sha2-nistp256
|       diffie-hellman-group14-sha256
|       diffie-hellman-group14-sha1
|       kexguess2@matt.ucc.asn.au
|   server_host_key_algorithms: (3)
|       ecdsa-sha2-nistp256
|       ssh-rsa
|       ssh-dss
|   encryption_algorithms: (6)
|       aes128-ctr
|       aes256-ctr
|       aes128-cbc
|       aes256-cbc
|       3des-ctr
|       3des-cbc
|   mac_algorithms: (2)
|       hmac-sha1
|       hmac-sha2-256
|   compression_algorithms: (1)
|_      none
MAC Address: E4:F4:C6:0D:91:F2 (Netgear)
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 2.26 seconds

Current Yocto 2.6

# nmap -p22 -n -sV --script ssh2-enum-algos 192.168.10.203
Starting Nmap 7.70 ( https://nmap.org ) at 2019-02-05 10:07 EST
Nmap scan report for 192.168.10.203
Host is up (0.00095s latency).

PORT   STATE SERVICE VERSION
22/tcp open  ssh     Dropbear sshd 2018.76 (protocol 2.0)
| ssh2-enum-algos:
|   kex_algorithms: (8)
|       curve25519-sha256
|       curve25519-sha256@libssh.org
|       ecdh-sha2-nistp521
|       ecdh-sha2-nistp384
|       ecdh-sha2-nistp256
|       diffie-hellman-group14-sha256
|       diffie-hellman-group14-sha1
|       kexguess2@matt.ucc.asn.au
|   server_host_key_algorithms: (1)
|       ssh-rsa
|   encryption_algorithms: (6)
|       aes128-ctr
|       aes256-ctr
|       aes128-cbc
|       aes256-cbc
|       3des-ctr
|       3des-cbc
|   mac_algorithms: (3)
|       hmac-sha1-96
|       hmac-sha1
|       hmac-sha2-256
|   compression_algorithms: (2)
|       zlib@openssh.com
|_      none
MAC Address: B8:27:EB:7B:E8:32 (Raspberry Pi Foundation)
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 2.19 seconds

Current Buildroot with BR2_PACKAGE_DROPBEAR_LEGACY_CRYPTO enabled (unsafe)

# nmap -p22 -n -sV --script ssh2-enum-algos 192.168.10.203
Starting Nmap 7.70 ( https://nmap.org ) at 2019-02-05 10:23 EST
Nmap scan report for 192.168.10.203
Host is up (0.00088s latency).

PORT   STATE SERVICE VERSION
22/tcp open  ssh     Dropbear sshd 2018.76 (protocol 2.0)
| ssh2-enum-algos:
|   kex_algorithms: (8)
|       curve25519-sha256
|       curve25519-sha256@libssh.org
|       ecdh-sha2-nistp521
|       ecdh-sha2-nistp384
|       ecdh-sha2-nistp256
|       diffie-hellman-group14-sha256
|       diffie-hellman-group14-sha1
|       kexguess2@matt.ucc.asn.au
|   server_host_key_algorithms: (3)
|       ecdsa-sha2-nistp256
|       ssh-rsa
|       ssh-dss
|   encryption_algorithms: (9)
|       aes128-ctr
|       aes256-ctr
|       aes128-cbc
|       aes256-cbc
|       twofish256-cbc
|       twofish-cbc
|       twofish128-cbc
|       3des-ctr
|       3des-cbc
|   mac_algorithms: (3)
|       hmac-sha1-96
|       hmac-sha1
|       hmac-sha2-256
|   compression_algorithms: (2)
|       zlib@openssh.com
|_      none
MAC Address: B8:27:EB:7B:E8:32 (Raspberry Pi Foundation)
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 2.21 seconds

And old version of Dropbear (2014.63)

# nmap -p2222 -n -sV --script ssh2-enum-algos 192.168.10.12
Starting Nmap 7.70 ( https://nmap.org ) at 2019-02-05 10:43 EST
Nmap scan report for 192.168.10.12
Host is up (0.00078s latency).

PORT     STATE SERVICE VERSION
2222/tcp open  ssh     Dropbear sshd 2014.63 (protocol 2.0)
| ssh2-enum-algos:
|   kex_algorithms: (7)
|       curve25519-sha256@libssh.org
|       ecdh-sha2-nistp521
|       ecdh-sha2-nistp384
|       ecdh-sha2-nistp256
|       diffie-hellman-group1-sha1
|       diffie-hellman-group14-sha1
|       kexguess2@matt.ucc.asn.au
|   server_host_key_algorithms: (3)
|       ecdsa-sha2-nistp521
|       ssh-rsa
|       ssh-dss
|   encryption_algorithms: (9)
|       aes128-ctr
|       3des-ctr
|       aes256-ctr
|       aes128-cbc
|       3des-cbc
|       aes256-cbc
|       twofish256-cbc
|       twofish-cbc
|       twofish128-cbc
|   mac_algorithms: (3)
|       hmac-sha1-96
|       hmac-sha1
|       hmac-md5
|   compression_algorithms: (3)
|       zlib
|       zlib@openssh.com
|_      none
MAC Address: 08:62:66:4C:29:91 (Asustek Computer)
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 2.20 seconds

Some results showing OpenSSH detection is not impacted

OpenBSD 6.4

# nmap -p22 -n -sV --script ssh2-enum-algos 192.168.10.2
Starting Nmap 7.70 ( https://nmap.org ) at 2019-02-05 10:37 EST
Nmap scan report for 192.168.10.2
Host is up (0.00051s latency).

PORT   STATE SERVICE VERSION
22/tcp open  ssh     OpenSSH 7.9 (protocol 2.0)
| ssh2-enum-algos:
|   kex_algorithms: (10)
|       curve25519-sha256
|       curve25519-sha256@libssh.org
|       ecdh-sha2-nistp256
|       ecdh-sha2-nistp384
|       ecdh-sha2-nistp521
|       diffie-hellman-group-exchange-sha256
|       diffie-hellman-group16-sha512
|       diffie-hellman-group18-sha512
|       diffie-hellman-group14-sha256
|       diffie-hellman-group14-sha1
|   server_host_key_algorithms: (5)
|       rsa-sha2-512
|       rsa-sha2-256
|       ssh-rsa
|       ecdsa-sha2-nistp256
|       ssh-ed25519
|   encryption_algorithms: (6)
|       chacha20-poly1305@openssh.com
|       aes128-ctr
|       aes192-ctr
|       aes256-ctr
|       aes128-gcm@openssh.com
|       aes256-gcm@openssh.com
|   mac_algorithms: (10)
|       umac-64-etm@openssh.com
|       umac-128-etm@openssh.com
|       hmac-sha2-256-etm@openssh.com
|       hmac-sha2-512-etm@openssh.com
|       hmac-sha1-etm@openssh.com
|       umac-64@openssh.com
|       umac-128@openssh.com
|       hmac-sha2-256
|       hmac-sha2-512
|       hmac-sha1
|   compression_algorithms: (2)
|       none
|_      zlib@openssh.com
MAC Address: 00:1D:7D:9D:3E:54 (Giga-byte Technology)

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 2.24 seconds

Ubuntu 16.04

# nmap -p22 -n -sV --script ssh2-enum-algos 192.168.10.12
Starting Nmap 7.70 ( https://nmap.org ) at 2019-02-05 10:39 EST
Nmap scan report for 192.168.10.12
Host is up (0.00076s latency).

PORT   STATE SERVICE VERSION
22/tcp open  ssh     OpenSSH 7.2p2 Ubuntu 4ubuntu2.6 (Ubuntu Linux; protocol 2.0)
| ssh2-enum-algos:
|   kex_algorithms: (6)
|       curve25519-sha256@libssh.org
|       ecdh-sha2-nistp256
|       ecdh-sha2-nistp384
|       ecdh-sha2-nistp521
|       diffie-hellman-group-exchange-sha256
|       diffie-hellman-group14-sha1
|   server_host_key_algorithms: (5)
|       ssh-rsa
|       rsa-sha2-512
|       rsa-sha2-256
|       ecdsa-sha2-nistp256
|       ssh-ed25519
|   encryption_algorithms: (6)
|       chacha20-poly1305@openssh.com
|       aes128-ctr
|       aes192-ctr
|       aes256-ctr
|       aes128-gcm@openssh.com
|       aes256-gcm@openssh.com
|   mac_algorithms: (10)
|       umac-64-etm@openssh.com
|       umac-128-etm@openssh.com
|       hmac-sha2-256-etm@openssh.com
|       hmac-sha2-512-etm@openssh.com
|       hmac-sha1-etm@openssh.com
|       umac-64@openssh.com
|       umac-128@openssh.com
|       hmac-sha2-256
|       hmac-sha2-512
|       hmac-sha1
|   compression_algorithms: (2)
|       none
|_      zlib@openssh.com
MAC Address: 08:62:66:4C:29:91 (Asustek Computer)
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 2.21 seconds
@aaronnad
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@aaronnad aaronnad commented Sep 11, 2020

+1 for this to be merged. Manually pulled the commit in to the file to scan some AP's using DropBear and this now returns with the information as expected

@nnposter
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@nnposter nnposter commented Sep 13, 2020

Thank you for identifying the issue and proposing a remediation.

A different, more general fix has been committed as r38025. Please give it a try and report back if it does not address the problem.

@nmap-bot nmap-bot closed this in fa6bd3f Sep 13, 2020
@nnposter nnposter self-assigned this Sep 14, 2020
@res0nat0r res0nat0r mentioned this pull request Oct 7, 2020
res0nat0r added a commit to res0nat0r/nmap that referenced this pull request Oct 7, 2020
* Implement Ncat proxy creds via environment variable. Fixes nmap#2060, closes nmap#2073

* Fix --resume from IPv6 scans

* Use correct default buffer position. Closes nmap#2084

* Clarify upper boundary for variable-length numerical fields

* Make maximize_fdlimit return rlim_t on appropriate platforms. Closes nmap#2085. Fixes nmap#2079

* Credential object is creds.Account, not brute.Account. See nmap#2086

* Clarify location of the Error object

* Use correct default buffer position. Closes nmap#2086

* Minor optimization of url.parse_query()

* Output of matched fingerprints in http-default-accounts. Fixes nmap#2077

* Document that --open implies --defeat-rst-ratelimit since 7.40

* SNMP scripts are enabled on non-standard ports. See nmap#1473

* Increases SQL Server version resolution

* Eliminate reflection false positives in http-shellshock. Closes nmap#2089

* Unify AFP pathname serialization

* Correct AFP name extraction from responses. Closes nmap#2091
FPGetFileDirParms and FPEnumerateExt2 could crash due to unpacking from
out-of-bounds positions. This latent issue got exposed by converting from
bin.unpack to more stringent string.unpack

* Clarified parsing of the volume list in AFP FPGetSrvrParms

* Add cross references between the 2 whois scripts

* Streamline Boolean expressions

* Centralize AFP timestamp conversion to string

* Fix a word-wrapping issue

* Prevent SSH2 KEX confusion. Fixes nmap#2105

* Add ssh2.fetch_host_key() support for group 16

* Handle case of corrupted TCP options with length 0. Fixes nmap#2104

* Add iDRAC9 fingerprint to http-default-accounts. Closes nmap#2096

* fix license url: http -> https

* Implementation of TLS SNI override in Ncat
Closes nmap#2087, closes nmap#1928, fixes nmap#1927, fixes nmap#1974

* Fix off-by-one issue in last change. Fixes nmap#2107

* Be more strict with TCP options parsing, avoid reading off the end of TCP options. See nmap#2107

* Remove nmap-update

This feature was never publicly released, and has not been distributed
in our binary builds for a couple versions now. It needed to be removed
in order to reduce the number of places Nmap looks for data files. See nmap#2051

* If fetchfile didn't find the XSL, use a relative path on all platforms.

* Do not search NMAPDATADIR on Windows as it is not defined. See nmap#2051

* Remove an unused variable

* Require trailing '/' to match a directory name with --script. See nmap#2051

* Stop using Shellshock in header name. Fixes nmap#1983

* Fix line wrapping

* Speed improvement for script afp-ls. Closes nmap#2098

* New option --discovery-ignore-rst. Closes nmap#1616

* Nbase is needed for __attribute__ on Windows

* include string_pool in Windows build

* Use larger buffer size for socket errors (WSAETIMEDOUT was longer).

* Allow multiple UDP payloads per port. Closes nmap#1859 (payloads to be committed later)

* New UDP payloads. Closes nmap#1860

* Use ASCII chars for some payload data where it makes sense

* Pass error along instead of printing (link error)

* OpenSSL 1.1.X renamed libs: libeay32->libcrypto ssleay32->libssl

* More OpenSSL DLL name changes

* One last libeay32->libcrypto name change

* Fix loopback detection on Windows with new Npcap

* Add some popular favicon hashes

* Update nmap-mac-prefixes

* Update nmap-services from IANA

* Handle too-short response in s7-info. See nmap#2117

* Remove a todo item that is done (--resolve-all)

* Update dated 'class' network terms to CIDR. Closes nmap#2054

* Call superclass's init method from derived class

* Use signed value for tcp header offset and option lengths to detect underflow

* Correctly check for unsigned subtraction underflow.

* Add some missing changelog entries

* Tell LGTM to use the correct version of Python (2)

* Process new Linux and OpenBSD fingerprints

* Only get SSL options if we use them, currently for NO_SSLv2

* Process a few service fingerprint submissions

* Add a requested feature

* Try to make sure enough data is present before parsing. See nmap#2117

* Replace hyphens in the client SSH banner
Hyphen is not allowed in the software version string (RFC 4253, section 4.2)

* Update the SSH protocol flow. Closes nmap#1460
Allows the server to start the key exchange before the protocol version
exchange (banner exchange) is completed

* Silence static analysis warning

LGTM points out that since comparison with sizeof(buf) coerces n to
unsigned, all negative values become very large values, which are
necessarily larger than sizeof(buf), so the test is redundant. We still
want the test in our code to be explicit that we are checking for it, so
reordering the comparisons should silence the warning. A good optimizing
compiler should be able to combine the two conditions anyway.

See github/codeql#4249

* Be explicit about truncating division (timeout is in whole milliseconds)

* Improve docs on -Pn and host discovery

"Host discovery" is the preferred term over "ping scan" because of
confusion with ICMP Echo Request, a.k.a. "ping" as used by the "ping"
utility. Warn when users use -Pn because it has negative impact on scan
times since ultrascan timing parameters fall back to slow initial
defaults.

* Fix a config issue with LGTM (libverbs not linked in libpcap)

* Update IPv6 classifier based on new submissions through 2020-09-14

* Fix a meaningless error message when parsing IPv6 extension headers.

* Allow %F date format to mean YYYY-mm-dd like GNU date

* Remove duplicate test conditionals already tested in enclosing block

* Properly handle pcap reads in iocp engine. Fixes nmap#2126

Still has an odd code smell, but this fixes my test case with Nping.

* Add missing prototype

* Make IOCP the default Nsock engine on Windows. See nmap#2126

* Update macosx build to OpenSSL 1.1.1h, use jhbuild for all build steps

* Default rule base for script mysql-audit. See nmap#2125

* Avoid masked use of date before 1/1/1970 UTC. Fixes nmap#2136, closes nmap#2137

* Fix a CHANGELOG typo

* Reintegrate Nmap 7.90 release branch

* Bump version and regen docs for 7.90SVN post-release

* Only warn about protocol specs in port list with -p. Fixes nmap#2135

* Handle a weird IOCP error for UDP sockets. Fixes nmap#2140

Co-authored-by: nnposter <nnposter@e0a8ed71-7df4-0310-8962-fdc924857419>
Co-authored-by: dmiller <dmiller@e0a8ed71-7df4-0310-8962-fdc924857419>
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