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Code Issues Releases Wiki Activity

Better fix to insecure password check (fixes #501)

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This commit is contained in:
Jay Berkenbilt 2021-02-04 20:32:00 -05:00
parent 63158cf546
commit 3de67173de
5 changed files with 63 additions and 63 deletions
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10
ChangeLog
View File

@ -5,11 +5,11 @@
Fixes #499.
* By default, give an error if a user attempts to encrypt a file
with an empty owner password or an owner password that is the same
as the user password. Such files are insecure. Most viewers either
won't open such files or will not enforce security settings. To
allow explicit creation of files like this, pass the new
--allow-insecure option. Fixes #501.
with a 256-bit key, a non-empty user password, and an empty owner
password. Such files are insecure since they can be opened with no
password. To allow explicit creation of files like this, pass the
new --allow-insecure option. Thanks to github user RobK88 for a
detailed analysis and for reporting this issue. Fixes #501.
2021-02-02 Jay Berkenbilt <ejb@ql.org>

62
manual/qpdf-manual.xml
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@ -1239,10 +1239,11 @@ make
<para>
Either or both of the user password and the owner password may be
empty strings. Starting in qpdf 10.2, qpdf defaults to not
allowing creation of PDF files with an empty owner password or an
owner password that matches the user password. If you want to
create such files, specify the encryption option
<option>--allow-insecure</option>, as described below.
allowing creation of PDF files with a non-empty user password, an
empty owner password, and a 256-bit key since such files can be
opened with no password. If you want to create such files, specify
the encryption option <option>--allow-insecure</option>, as
described below.
</para>
<para>
The value for
@ -1251,25 +1252,6 @@ make
When no additional restrictions are given, the default is to be
fully permissive.
</para>
<para>
For all key lengths, the following options are available:
<variablelist>
<varlistentry>
<term><option>--allow-insecure</option></term>
<listitem>
<para>
From qpdf 10.2, qpdf defaults to not allowing creation of PDF
files where the owner password is blank or matches the user
password. Files created in this way are insecure and can't be
opened by some viewers. Users would ordinarily never want to
create such files. If you are using qpdf to intentionally
created strange files for testing (a definite valid use of
qpdf!), this option allows you to create such insecure files.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
If <option><replaceable>key-length</replaceable></option> is 40,
the following restriction options are available:
@ -1465,6 +1447,21 @@ make
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--allow-insecure</option></term>
<listitem>
<para>
From qpdf 10.2, qpdf defaults to not allowing creation of PDF
files where the user password is non-empty, the owner password
is empty, and a 256-bit key is in use. Files created in this
way are insecure since they can be opened without a password.
Users would ordinarily never want to create such files. If you
are using qpdf to intentionally created strange files for
testing (a definite valid use of qpdf!), this option allows
you to create such insecure files.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--force-V4</option></term>
<listitem>
@ -4877,15 +4874,16 @@ print "\n";
<listitem>
<para>
By default, <command>qpdf</command> no longer allows
creation of encrypted PDF files whose owner password is
empty or matches the user password. The
<option>--allow-insecure</option>, specified inside the
<option>--encrypt</option> options, allows creation of such
files. Behavior changes in the CLI are avoided when
possible, but an exception was made here because this is
security-related. qpdf must always allow creation of weird
files for testing purposes, but it should not default to
letting users unknowingly create insecure files.
creation of encrypted PDF files whose user password is
non-empty and owner password is empty when a 256-bit key is
in use. The <option>--allow-insecure</option> option,
specified inside the <option>--encrypt</option> options,
allows creation of such files. Behavior changes in the CLI
are avoided when possible, but an exception was made here
because this is security-related. qpdf must always allow
creation of weird files for testing purposes, but it should
not default to letting users unknowingly create insecure
files.
</para>
</listitem>
</itemizedlist>

31
qpdf/qpdf.cc
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@ -1082,7 +1082,6 @@ ArgParser::initOptionTable()
t = &this->encrypt40_option_table;
(*t)["--"] = oe_bare(&ArgParser::argEndEncrypt);
(*t)["allow-insecure"] = oe_bare(&ArgParser::argAllowInsecure);
// The above 40-bit options are also 128-bit and 256-bit options,
// so copy what we have so far to 128. Then continue separately
// with 128. We later copy 128 to 256.
@ -1117,6 +1116,7 @@ ArgParser::initOptionTable()
t = &this->encrypt256_option_table;
(*t)["force-R5"] = oe_bare(&ArgParser::arg256ForceR5);
(*t)["allow-insecure"] = oe_bare(&ArgParser::argAllowInsecure);
t = &this->under_overlay_option_table;
(*t)[""] = oe_positional(&ArgParser::argUOpositional);
@ -1333,10 +1333,6 @@ ArgParser::argHelp()
<< "\n"
<< "Additional flags are dependent upon key length.\n"
<< "\n"
<< " For all key lengths:\n"
<< " --allow-insecure allow the owner password to be empty or the\n"
<< " same as the user password\n"
<< "\n"
<< " If 40:\n"
<< "\n"
<< " --print=[yn] allow printing\n"
@ -1362,6 +1358,9 @@ ArgParser::argHelp()
<< " --force-V4 this option is not available with 256-bit keys\n"
<< " --use-aes this option is always on with 256-bit keys\n"
<< " --force-R5 forces use of deprecated R=5 encryption\n"
<< " --allow-insecure allow the owner password to be empty when the\n"
<< " user password is not empty\n"
<< "\n"
<< "\n"
<< " print-opt may be:\n"
<< "\n"
@ -3394,15 +3393,21 @@ ArgParser::doFinalChecks()
}
if (o.encrypt && (! o.allow_insecure) &&
(o.owner_password.empty() ||
(o.owner_password == o.user_password)))
(o.owner_password.empty() &&
(! o.user_password.empty()) &&
(o.keylen == 256)))
{
usage("An encrypted PDF with an empty owner password or an"
" owner password that is the same as a user password"
" is insecure and can't be opened by some viewers. If you"
" really want to do this, you must also give the"
" --allow-insecure option before the -- that follows"
" --encrypt.");
// Note that empty owner passwords for R < 5 are copied from
// the user password, so this lack of security is not an issue
// for those files. Also we are consider only the ability to
// open the file without a password to be insecure. We are not
// concerned about whether the viwer enforces security
// settings when the user and owner password match.
usage("A PDF with a non-empty user password and an empty owner"
" password encrypted with a 256-bit key is insecure as it"
" can be opened without a password. If you really want to"
" do this, you must also give the --allow-insecure option"
" before the -- that follows --encrypt.");
}
if (o.require_outfile && o.outfilename &&

15
qpdf/qtest/qpdf.test
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@ -3464,7 +3464,7 @@ my @encrypted_files =
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1],
);
$n_tests += 9 + (2 * (@encrypted_files)) + (7 * (@encrypted_files - 6)) + 9;
$n_tests += 8 + (2 * (@encrypted_files)) + (7 * (@encrypted_files - 6)) + 9;
$td->runtest("encrypted file",
{$td->COMMAND => "test_driver 2 encrypted-with-images.pdf"},
@ -3482,17 +3482,12 @@ $td->runtest("recheck encrypted file",
$td->NORMALIZE_NEWLINES);
$td->runtest("empty owner password",
{$td->COMMAND => "qpdf --encrypt '' '' 128 -- minimal.pdf a.pdf"},
{$td->REGEXP => ".*is insecure.*--allow-insecure.*",
$td->EXIT_STATUS => 2},
$td->NORMALIZE_NEWLINES);
$td->runtest("matching user/owner password",
{$td->COMMAND => "qpdf --encrypt q q 128 -- minimal.pdf a.pdf"},
{$td->COMMAND => "qpdf --encrypt u '' 256 -- minimal.pdf a.pdf"},
{$td->REGEXP => ".*is insecure.*--allow-insecure.*",
$td->EXIT_STATUS => 2},
$td->NORMALIZE_NEWLINES);
$td->runtest("allow insecure",
{$td->COMMAND => "qpdf --encrypt '' '' 128 --allow-insecure --" .
{$td->COMMAND => "qpdf --encrypt u '' 256 --allow-insecure --" .
" minimal.pdf a.pdf"},
{$td->STRING => "", $td->EXIT_STATUS => 0},
$td->NORMALIZE_NEWLINES);
@ -3630,7 +3625,7 @@ foreach my $d (@encrypted_files)
$enc_json =~ s/---upm---/$upm/;
my $eflags = "-encrypt \"$upass\" \"$opass\" $bits $xeflags --";
if (($opass eq "") || ($opass eq $upass))
if (($opass eq "") && ($bits == 256))
{
$eflags =~ s/--$/--allow-insecure --/;
}
@ -3892,7 +3887,7 @@ foreach my $d (['--force-V4', 'V4'],
my ($args, $out) = @$d;
$td->runtest("encrypt $args",
{$td->COMMAND => "qpdf --static-aes-iv --static-id" .
" --encrypt '' '' 128 $args --allow-insecure --" .
" --encrypt '' '' 128 $args --" .
" enc-base.pdf a.pdf"},
{$td->STRING => "", $td->EXIT_STATUS => 0});
$td->runtest("check output",

8
qpdf/qtest/qpdf/insecure-passwords.out
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@ -1,10 +1,9 @@
checking a.pdf
PDF Version: 1.4
R = 3
PDF Version: 1.7 extension level 8
R = 6
P = -4
User password =
Supplied password is owner password
Supplied password is user password
extract for accessibility: allowed
extract for any purpose: allowed
print low resolution: allowed
@ -14,6 +13,9 @@ modify forms: allowed
modify annotations: allowed
modify other: allowed
modify anything: allowed
stream encryption method: AESv3
string encryption method: AESv3
file encryption method: AESv3
File is not linearized
No syntax or stream encoding errors found; the file may still contain
errors that qpdf cannot detect