A proof-of-concept WordPress plugin fuzzer used in the research described in https://kazet.cc/2022/02/03/fuzzing-wordpress-plugins.html that helped to discover more than 120 vulnerablities in WordPress plugins installed on more than 10 million sites.
If you want to continue the research, start with less popular plugins - if a plugin achieved at least 10k active installs between October 2021 and January 2022, I have most probably looked at the fuzzer reports (and most focus has been put on plugins having at least 20k active installs). Because there is a lot of randomness in how fuzzer works, some vulnerabilities in these plugins remain undiscovered - but fewer ones.
Fuzzer reports contain a lot of false positives - most of them don't indicate a vulnerability. After seeing a report, first analyze whether the behavior you're observing is indeed a vulnerability or a false positive. Don't spam WPScan/vendors with raw fuzzer reports - provide a PoC exploit instead.
For obvious reasons, the examples will contain only vulnerabilities that have already been fixed.
Let's assume you are fuzzing responsive-vector-maps
in version 6.4.0:
./bin/fuzz_plugin responsive-vector-maps --version 6.4.0
(to fuzz the latest version, just skip --version
).
After the fuzzing finishes (which would take 10-30 minutes for this plugin) you can call:
./bin/print_findings data/plugin_fuzz_results/
You will see, among others:
That means that the fuzzer detected executing fopen()
on a known payload.
Most of the payloads contain the word GARLIC
in them to facilitate automatic
detection in output. You may see or configure them in docker_image/magic_payloads.php
.
Then, you may browse the source code and see that indeed the wp_ajax_rvm_import_markers
endpoint uses the file content to render output, thus allowing you to read arbitrary files
on the server: CVE-2021-24947.
What you see in white is a crash considered interesting (you may modify them or add new ones
in crash_detectors.py
). Green is the context. In blue you see the report file name
(with plugin name), plugin popularity and endpoint name (here: the ajax action name).
The data in yellow are what payloads were injected into what variables.
Let's assume you are fuzzing page-builder-add
in version 1.4.9.4:
./bin/fuzz_plugin page-builder-add --version 1.4.9.4
After printing the results, you will see known payload echoed back:
You can then manually test whether indeed this place (remember: in blue you have the endpoint name, here: the menu page name) is vulnerable to XSS. In this case, it is: CVE-2021-25067.
./bin/fuzz_plugin duplicate-page-or-post --version 1.4.6
After printing the results, you will see update_option
being called:
Analysis of the endpoint's code will tell you that this indeed leads to a stored XSS vulnerability: CVE-2021-25075.
Unfortunately, for most of the plugins the fuzzer doesn't find any interesting crashes, and for the rest, most of the reports are false positives. For example, if you see:
Call: wp_mail arguments={'to': 'plugin@pluginvendor.com', 'subject': '[Plugin contact] - http://GARLICGARLICGARLIC.example.com'}
This can mean, that wp_mail
is indeed called, but you don't control the recipient
and most of the subject. If you want to be sure, look at the plugin source.
- If you see the message; May as well be equal: ... and ... - that means that the mechanism to pretend that a known payload is equal to any other string (described in https://kazet.cc/2022/02/03/fuzzing-wordpress-plugins.html#patched-equality) was triggered.
- If you see
__GARLIC_ACCESSED__ _FILES[files] __ENDGARLIC__
- that means that an uploaded file access was detected. No further checks are currently made - to check whether this is a vulnerability, look at the code. - Sometimes what the fuzzer injects into GET, POST etc. parameters is not reproducible in the real world:
for example, you can't inject anything into
$_GET['page']
if you want a particular menu page to be displayed.
The first run of fuzzing or of the tests may take about an hour, because we need to build the Docker image with instrumented PHP and WordPress.
./bin/fuzz_plugin PLUGIN_SLUG
To print what the fuzzer found, use:
./bin/print_findings data/plugin_fuzz_results/
To run the tests, use:
./bin/test
Warning: the tests take long (more than an hour) and because they check whether the fuzzer would find vulnerabilities, they fail with some probability.
To reformat and check the code, use:
./bin/reformat
You may start a test environment with only one plugin installed using:
./bin/manual_testing PLUGIN_SLUG
It will listen on http://127.0.0.1:8001/
There will be two test users in the database:
- username: admin, password: admin, privileges: administrator
- username: subscriber, password: subscriber, privileges: subscriber
This tool is a proof of concept - this section contains places where it can be improved to find more vulnerabilities.
You may want to edit filtering.py
-- it contains the rules that deem a particular crash
important or not. If you change them, you may have more false positives, but find more vulnerabilities
as well. For example, the only header that I consider interesting when emitted is the Location
header, to detect Open Redirect vulnerabilities. That is just one idea and you may have others.
Another file that may be worth extending is docker_image/patch_wordpress.sh
. It describes
calls to which functions will be logged as interesting.
If you want to inject other payloads (or change the probabilities with which they are injected)
edit docker_image/magic_payloads.php
and docker_image/fuzz/config.py
.
crash_detector.py
contans regular expressions that find interesting crashes or interesting
information (e.g. e-mails) being exposed.
Fuzzing files (i.e. executing each PHP file with injected payloads) has been disabled
because it didn't lead to many findings. Uncomment files
in config.DEFAULT_ENABLED_FEATURES
to change that.
Maybe. Install the plugin in a local test environment (for example you may use the one described in the Manual testing environment section) and analyze the bug.
Don't assume that. The fuzzer finds some classes of vulnerabilities, but has its limitations.
Fuzzer founds nothing for most of the plugins - the purpose of the tool is rather to massively scan a large number of Wordpress plugins, not to perform comprehensive tests of a single plugin.
File a Github ticket or e-mail me: kazet@p4.team.