Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

fixed regexes to avoid ReDoS attacks #10

Merged
merged 2 commits into from
May 25, 2021
Merged

fixed regexes to avoid ReDoS attacks #10

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
09e1086
fixed regexes to avoid ReDoS attacks
jeffrey-pinyan-ithreat May 13, 2021
d8b5e6b
streamlined regexes, simplified parse() returns
jeffrey-pinyan-ithreat May 13, 2021
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
1 change: 1 addition & 0 deletions .npmignore
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,2 +1,3 @@
.travis.yml
redos.js
test.js
52 changes: 17 additions & 35 deletions index.js
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -2,29 +2,14 @@

var isWindows = process.platform === 'win32';

// Regex to split a windows path into three parts: [*, device, slash,
// tail] windows-only
var splitDeviceRe =
/^([a-zA-Z]:|[\\\/]{2}[^\\\/]+[\\\/]+[^\\\/]+)?([\\\/])?([\s\S]*?)$/;

// Regex to split the tail part of the above into [*, dir, basename, ext]
var splitTailRe =
/^([\s\S]*?)((?:\.{1,2}|[^\\\/]+?|)(\.[^.\/\\]*|))(?:[\\\/]*)$/;
// Regex to split a windows path into into [dir, root, basename, name, ext]
var splitWindowsRe =
/^(((?:[a-zA-Z]:|[\\\/]{2}[^\\\/]+[\\\/]+[^\\\/]+)?[\\\/]?)(?:[^\\\/]*[\\\/])*)((\.{1,2}|[^\\\/]+?|)(\.[^.\/\\]*|))[\\\/]*$/;

var win32 = {};

// Function to split a filename into [root, dir, basename, ext]
function win32SplitPath(filename) {
// Separate device+slash from tail
var result = splitDeviceRe.exec(filename),
device = (result[1] || '') + (result[2] || ''),
tail = result[3] || '';
// Split the tail into dir, basename and extension
var result2 = splitTailRe.exec(tail),
dir = result2[1],
basename = result2[2],
ext = result2[3];
return [device, dir, basename, ext];
return splitWindowsRe.exec(filename).slice(1);
}

win32.parse = function(pathString) {
Expand All @@ -34,24 +19,24 @@ win32.parse = function(pathString) {
);
}
var allParts = win32SplitPath(pathString);
if (!allParts || allParts.length !== 4) {
if (!allParts || allParts.length !== 5) {
throw new TypeError("Invalid path '" + pathString + "'");
}
return {
root: allParts[0],
dir: allParts[0] + allParts[1].slice(0, -1),
root: allParts[1],
dir: allParts[0] === allParts[1] ? allParts[0] : allParts[0].slice(0, -1),
base: allParts[2],
ext: allParts[3],
name: allParts[2].slice(0, allParts[2].length - allParts[3].length)
ext: allParts[4],
name: allParts[3]
};
};



// Split a filename into [root, dir, basename, ext], unix version
// Split a filename into [dir, root, basename, name, ext], unix version
// 'root' is just a slash, or nothing.
var splitPathRe =
/^(\/?|)([\s\S]*?)((?:\.{1,2}|[^\/]+?|)(\.[^.\/]*|))(?:[\/]*)$/;
/^((\/?)(?:[^\/]*\/)*)((\.{1,2}|[^\/]+?|)(\.[^.\/]*|))[\/]*$/;
Copy link

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

These look like breaking changes to me, and I am not entirely sure if this fixes the DoS. I did a little work on this issue. It is tempting to fix the groups, the whitespace (\s\S), etc., but I found that the existing unit tests were incomplete (even if some are unrealistic).

I found that these tests needed to be added:

var regexDosFileNameLength = 50000;
var regexDosFileName = Buffer.alloc(regexDosFileNameLength, '/').toString() + 'file.txt';

[{ root: '/', dir: '/home/user/dir', base: 'file.txt', ext: '.txt', name: 'file' }, '/home/user/dir/file.txt/'],
[{ root: '/', dir: '/\n\thome/user/dir', base: 'file.txt', ext: '.txt', name: 'file' }, '/\n\thome/user/dir/file.txt/'],
[{ root: '/', dir: '/////////', base: 'file.txt', ext: '.txt', name: 'file' }, '//////////file.txt'],
[{ root: '/', dir: '/', base: '', ext: '', name: '' }, '//////////'],
[{ root: '/', dir: Buffer.alloc(regexDosFileNameLength - 1, '/').toString(), base: 'file.txt', ext: '.txt', name: 'file' }, regexDosFileName],
 ];

If you want these to be breaking changes, then fine. The regexDosFileNameLength is specifically to test the regex DoS.

Copy link
Contributor Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I can pass those tests with

var splitPathRe =
  /^((\/?)(?:[^\/]*\/)*)((\.{1,2}|[^\/]+?|)(\.[^.\/]*|))(?:(?<=^\/)|(?<!\/))[\/]*$/;`

return {
  // ...
  dir: allParts[0] === '/' ? allparts[0] : allParts[0].slice(0, -1),
  // ...
}

But as thrilling as it is to have a single regex handling the parsing, it'd be much wiser to clean up the parameter (e.g. by stripping trailing slashes, while retaining a leading slash) and keeping the regex simple.

And as for avoiding the ReDoS, my testing shows a significant improvement:

attack_str.length: 1970001: 332 ms
attack_str.length: 1980001: 359 ms
attack_str.length: 1990001: 385 ms
attack_str.length: 2000001: 295 ms

var posix = {};


Expand All @@ -67,19 +52,16 @@ posix.parse = function(pathString) {
);
}
var allParts = posixSplitPath(pathString);
if (!allParts || allParts.length !== 4) {
if (!allParts || allParts.length !== 5) {
throw new TypeError("Invalid path '" + pathString + "'");
}
allParts[1] = allParts[1] || '';
allParts[2] = allParts[2] || '';
allParts[3] = allParts[3] || '';


return {
root: allParts[0],
dir: allParts[0] + allParts[1].slice(0, -1),
root: allParts[1],
dir: allParts[0].slice(0, -1),
base: allParts[2],
ext: allParts[3],
name: allParts[2].slice(0, allParts[2].length - allParts[3].length)
ext: allParts[4],
name: allParts[3],
};
};

Expand Down
20 changes: 20 additions & 0 deletions redos.js
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,20 @@
var pathParse = require('.');

function build_attack(n) {
var ret = ""
for (var i = 0; i < n; i++) {
ret += "/"
}
return ret + "◎";
}

for(var i = 1; i <= 5000000; i++) {
if (i % 10000 == 0) {
var time = Date.now();
var attack_str = build_attack(i)
pathParse.posix(attack_str);
pathParse.win32(attack_str);
var time_cost = Date.now() - time;
console.log("attack_str.length: " + attack_str.length + ": " + time_cost+" ms")
}
}