post: phishing-filter

source/_posts/phishing-filter.md

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+---
+title: Block phishing websites with phishing-filter
+excerpt: Many formats available
+date: 2020-07-07
+tags:
+- security
+---
+
+> Skip to [phishing-filter](#phishing-filter) section
+
+Recently I switched Firefox's Android app from Preview Nightly to Nightly after the former has been [deprecated](https://old.reddit.com/r/Android/comments/hk37jl/firefox_preview_has_been_merged_into_firefox/). The switch entailed migrating the configurations; a config I need to migrate over is DNS-over-HTTPS (DoH). I verified the Quad9's DoH address through its [instruction page](https://www.quad9.net/doh-quad9-dns-servers/) (tips: you can use "https://9.9.9.9/dns-query" instead of "https://dns.quad9.net/dns-query" so that a browser doesn't need to query the IP behind dns.quad9.net). I also checked out its [recent article](https://quad9.net/dns-blocking-effectiveness-recent-independent-tests/) that talks about how effective it blocks malicious and phishing websites (via DNS-blocking) compared to other well-known DNS service, like Cloudflare and OpenDNS. According to this [replication test](https://www.andryou.com/2020/05/31/comparing-malware-blocking-dns-resolvers-redux/), the effectiveness was measured based on the [DShield.org Suspicious Domain List](https://isc.sans.edu/suspicious_domains.html), which in turn was based on [PhishTank](https://www.phishtank.com/) and [URLhaus](https://urlhaus.abuse.ch/) lists.
+
+I was intrigued by the DShield list as I created a blocklist ([urlhaus-filter](https://gitlab.com/curben/urlhaus-filter)) that is also based on URLhaus. I then checked out its another source, the PhishTank list. PhishTank operates similarly to URLhaus, the links are user-submitted. User can vote on submitted links (of other users') are indeed phishing websites. The database is available in [various formats](https://www.phishtank.com/developer_info.php) including CSV. This seemed ideal to be processed into a blocklist, just like what I did in urlhaus-filter. To avoid duplicate effort, I did a search on FilterLists and there is a domain-based blocklist ("[Phishing Bad Sites](https://filterlists.com/lists/phishing-bad-sites)") that is based on PhishTank.
+
+Domain-based blocklist is created by stripping out the path of the original links, leaving the domain only (e.g. `www.example.com`~~`/foo-page`~~). This blocks the whole website, instead of specific webpages; it also significantly reduces the file size, not just from the path stripping, but also de-duplication of domains. However, one thing I learned from urlhaus-filter is that many malicious links are also hosted on popular domains, like Google Docs and Dropbox; such is the fate of file-hosting service, it will inadvertently be abused to host malicious content. To avoid blocking those popular services, I utilise [Umbrella Popularity List](https://s3-us-west-1.amazonaws.com/umbrella-static/index.html) and [Tranco List](https://tranco-list.eu/) to remove popular domains from urlhaus-filter. Since uBlock Origin (uBO) supports blocking webpages via static filter (e.g. `||example.com/foo-page$all`), malicious webpages (of popular domains) are still blocked in the [uBO-specific filter](https://gitlab.com/curben/urlhaus-filter#url-based).
+
+I ran a quick check on "Phishing Bad Sites" filter:
+
+```
+$ grep -F 'google' 2020-07-07-phishing.bad.sites.conf
+```
+
+The search result included Google Drive and Google Play.
+
+## phishing-filter
+
+I presents [phishing-filter](https://gitlab.com/curben/phishing-filter), a blocklist to restrict >14K phishing websites. [uBlock Origin](https://github.com/gorhill/uBlock) (uBO) users can import [phishing-filter.txt](https://gitlab.com/curben/phishing-filter/raw/master/dist/phishing-filter.txt) to install the filter. Other formats includes domain-based, hosts-based, dnsmasq, bind and unbound, refer to the repository for installation guide. The blocklist utilises similar approach as urlhaus-filter to exclude popular domains. Phishing links found in popular domains are still included in the "phishing-filter.txt", hence I recommend to use uBO for best result.
+
+The workflow is largely similar to what I did in urlhaus-filter, so I don't have to reinvent the wheel here. I did take the opportunity to improve the repository's folder structure, which I find a bit messy in urlhaus-filter. urlhaus-filter's folder structure is still retained as is because changing it would induce breaking change. In phishing-filter, all generated filters are put in `dist/` folder, taking a page from Javascript/NPM libraries. All scripts are in `src/` folder and `utils` folder contains [csvquote](https://github.com/dbro/csvquote) binaries.
+
+csvquote is a workaround for the use of _optional_ quote in PhishTank database. A URL is quoted only when there is a comma.
+
+```
+1,http://example-phishing.com/lorem,...
+2,"http://example-phishing.net/ipsum,dolor",...
+```
+
+This makes `cut` having incorrect result, the comma in the link is trimmed off,
+
+```
+$ cat phishtank.csv | cut -f 2 -d ","
+http://example-phishing.com/lorem
+"https://example.phishing.net/ipsum
+```
+
+csvquote works by escaping the comma(s) in the column and then un-escape back.
+
+```
+$ cat phishtank.csv | csvquote | cut -f 2 -d "," | csvquote -u
+http://example-phishing.com/lorem
+"https://example.phishing.net/ipsum,ipsum"
+```
+
+I then remove the quotes with `sed 's/"//g'`. It will be more convenient if _all_ URLs are quoted--just like URLhaus.csv--I can simply use `cut -f 2 -d '"'`. I know I'm not supposed to use `cut` to process csv, but there is no csv-processing command line tools available in Alpine Linux official packages.