We used the VNC API $ticket as password for VNC, but QEMU limits the
password to the first 8 chars and ignores the rest[0].
As our tickets start with a static string (e.g., "PVE") the entropy
was a bit limited.
For Proxmox VE this does not matters much as the noVNC viewer
provided by has to go always over the API call, and so a valid
ticket and correct permissions for the requested VM are enforced
anyway.
This patch helps external users, which often use NoVNC-Websockify,
circumventing the API and relying solely on the VNC password to avoid
snooping on VNC sessions.
A 'generate-password' parameter is added, if set a password from good
entropy (using libopenssl) is generated.
For simplicity of mapping random bits to ranges we extract 6 bit of
entropy per character and add the integer value of '!' (first
printable ASCII char) to that. This way we get 64^8 possibilities,
which even with millions of guesses per second one would need years
of guessing and mostly just DDOS the server with websocket upgrade
requests.
Signed-off-by: Thomas Lamprecht <t.lampre...@proxmox.com>
---
We could also extract the last 8 chars of the ticket, but as that ticket is
only secure as a whole, as seen with this issue, I'd like to avoid that
Initially I had a variant with using perls core rand and all 95 printable ascii
chars, but that wasn't crypthographical secure
PVE/API2/Qemu.pm | 39 ++++++++++++++++++++++++++++++++++++---
1 file changed, 36 insertions(+), 3 deletions(-)
diff --git a/PVE/API2/Qemu.pm b/PVE/API2/Qemu.pm
index 3e0d59f..dcb364d 100644
--- a/PVE/API2/Qemu.pm
+++ b/PVE/API2/Qemu.pm
@@ -7,6 +7,7 @@ use Net::SSLeay;
use POSIX;
use IO::Socket::IP;
use URI::Escape;
+use Crypt::OpenSSL::Random;
use PVE::Cluster qw (cfs_read_file cfs_write_file);;
use PVE::RRD;
@@ -1589,6 +1590,19 @@ __PACKAGE__->register_method({
return undef;
}});
+# uses good entropy, each char is limited to 6 bit to get printable chars simply
+my $gen_rand_chars = sub {
+ my ($length) = @_;
+
+ die "invalid length $length" if $length < 1;
+
+ my $min = ord('!'); # first printable ascii
+ my @rand_bytes = split '', Crypt::OpenSSL::Random::random_bytes($length);
+ my $str = join('', map { chr((ord($_) & 0x3F) + $min) } @rand_bytes);
+
+ return $str;
+};
+
my $sslcert;
__PACKAGE__->register_method({
@@ -1610,6 +1624,12 @@ __PACKAGE__->register_method({
type => 'boolean',
description => "starts websockify instead of vncproxy",
},
+ 'generate-password' => {
+ optional => 1,
+ type => 'boolean',
+ default => 0,
+ description => "Generates a random password to be used as ticket
instead of the API ticket.",
+ },
},
},
returns => {
@@ -1617,6 +1637,12 @@ __PACKAGE__->register_method({
properties => {
user => { type => 'string' },
ticket => { type => 'string' },
+ password => {
+ optional => 1,
+ description => "Returned if requested with 'generate-password'
param."
+ ." Consists of printable ASCII characters ('!' .. '~').",
+ type => 'string',
+ },
cert => { type => 'string' },
port => { type => 'integer' },
upid => { type => 'string' },
@@ -1644,6 +1670,10 @@ __PACKAGE__->register_method({
my $authpath = "/vms/$vmid";
my $ticket = PVE::AccessControl::assemble_vnc_ticket($authuser, $authpath);
+ my $password = $ticket;
+ if ($param->{'generate-password'}) {
+ $password = $gen_rand_chars->(8);
+ }
$sslcert = PVE::Tools::file_get_contents("/etc/pve/pve-root-ca.pem", 8192)
if !$sslcert;
@@ -1680,7 +1710,7 @@ __PACKAGE__->register_method({
'-perm', 'Sys.Console'];
if ($param->{websocket}) {
- $ENV{PVE_VNC_TICKET} = $ticket; # pass ticket to vncterm
+ $ENV{PVE_VNC_TICKET} = $password; # pass ticket to vncterm
push @$cmd, '-notls', '-listen', 'localhost';
}
@@ -1690,7 +1720,7 @@ __PACKAGE__->register_method({
} else {
- $ENV{LC_PVE_TICKET} = $ticket if $websocket; # set ticket with "qm vncproxy"
+ $ENV{LC_PVE_TICKET} = $password if $websocket; # set ticket with "qm
vncproxy"
$cmd = [@$remcmd, "/usr/sbin/qm", 'vncproxy', $vmid];
@@ -1725,13 +1755,16 @@ __PACKAGE__->register_method({
PVE::Tools::wait_for_vnc_port($port);
- return {
+ my $res = {
user => $authuser,
ticket => $ticket,
port => $port,
upid => $upid,
cert => $sslcert,
};
+ $res->{password} = $password if $param->{'generate-password'};
+
+ return $res;
}});
__PACKAGE__->register_method({
