All the vulnerabilities related to the version 5.32.0 of the package
express vulnerable to XSS via response.redirect()
In express <4.20.0, passing untrusted user input - even after sanitizing it - to response.redirect() may execute untrusted code
this issue is patched in express 4.20.0
users are encouraged to upgrade to the patched version of express, but otherwise can workaround this issue by making sure any untrusted inputs are safe, ideally by validating them against an explicit allowlist
successful exploitation of this vector requires the following:
send vulnerable to template injection that can lead to XSS
passing untrusted user input - even after sanitizing it - to SendStream.redirect() may execute untrusted code
this issue is patched in send 0.19.0
users are encouraged to upgrade to the patched version of express, but otherwise can workaround this issue by making sure any untrusted inputs are safe, ideally by validating them against an explicit allowlist
successful exploitation of this vector requires the following:
cookie accepts cookie name, path, and domain with out of bounds characters
The cookie name could be used to set other fields of the cookie, resulting in an unexpected cookie value. For example, serialize("userName=<script>alert('XSS3')</script>; Max-Age=2592000; a", value) would result in "userName=<script>alert('XSS3')</script>; Max-Age=2592000; a=test", setting userName cookie to <script> and ignoring value.
A similar escape can be used for path and domain, which could be abused to alter other fields of the cookie.
Upgrade to 0.7.0, which updates the validation for name, path, and domain.
Avoid passing untrusted or arbitrary values for these fields, ensure they are set by the application instead of user input.
body-parser vulnerable to denial of service when url encoding is enabled
body-parser <1.20.3 is vulnerable to denial of service when url encoding is enabled. A malicious actor using a specially crafted payload could flood the server with a large number of requests, resulting in denial of service.
this issue is patched in 1.20.3
serve-static vulnerable to template injection that can lead to XSS
passing untrusted user input - even after sanitizing it - to redirect() may execute untrusted code
this issue is patched in serve-static 1.16.0
users are encouraged to upgrade to the patched version of express, but otherwise can workaround this issue by making sure any untrusted inputs are safe, ideally by validating them against an explicit allowlist
successful exploitation of this vector requires the following:
path-to-regexp outputs backtracking regular expressions
A bad regular expression is generated any time you have two parameters within a single segment, separated by something that is not a period (.). For example, /:a-:b.
For users of 0.1, upgrade to 0.1.10. All other users should upgrade to 8.0.0.
These versions add backtrack protection when a custom regex pattern is not provided:
They do not protect against vulnerable user supplied capture groups. Protecting against explicit user patterns is out of scope for old versions and not considered a vulnerability.
Version 7.1.0 can enable strict: true and get an error when the regular expression might be bad.
Version 8.0.0 removes the features that can cause a ReDoS.
All versions can be patched by providing a custom regular expression for parameters after the first in a single segment. As long as the custom regular expression does not match the text before the parameter, you will be safe. For example, change /:a-:b to /:a-:b([^-/]+).
If paths cannot be rewritten and versions cannot be upgraded, another alternative is to limit the URL length. For example, halving the attack string improves performance by 4x faster.
Using /:a-:b will produce the regular expression /^\/([^\/]+?)-([^\/]+?)\/?$/. This can be exploited by a path such as /a${'-a'.repeat(8_000)}/a. OWASP has a good example of why this occurs, but the TL;DR is the /a at the end ensures this route would never match but due to naive backtracking it will still attempt every combination of the :a-:b on the repeated 8,000 -a.
Because JavaScript is single threaded and regex matching runs on the main thread, poor performance will block the event loop and can lead to a DoS. In local benchmarks, exploiting the unsafe regex will result in performance that is over 1000x worse than the safe regex. In a more realistic environment using Express v4 and 10 concurrent connections, this translated to average latency of ~600ms vs 1ms.
path-to-regexp contains a ReDoS
The regular expression that is vulnerable to backtracking can be generated in versions before 0.1.12 of path-to-regexp, originally reported in CVE-2024-45296
Upgrade to 0.1.12.
Avoid using two parameters within a single path segment, when the separator is not . (e.g. no /:a-:b). Alternatively, you can define the regex used for both parameters and ensure they do not overlap to allow backtracking.
on-headers is vulnerable to http response header manipulation
A bug in on-headers versions < 1.1.0 may result in response headers being inadvertently modified when an array is passed to response.writeHead()
Users should upgrade to 1.1.0
Uses are encouraged to upgrade to 1.1.0, but this issue can be worked around by passing an object to response.writeHead() rather than an array.
form-data uses unsafe random function in form-data for choosing boundary
form-data uses Math.random() to select a boundary value for multipart form-encoded data. This can lead to a security issue if an attacker:
Because the values of Math.random() are pseudo-random and predictable (see: https://blog.securityevaluators.com/hacking-the-javascript-lottery-80cc437e3b7f), an attacker who can observe a few sequential values can determine the state of the PRNG and predict future values, includes those used to generate form-data's boundary value. The allows the attacker to craft a value that contains a boundary value, allowing them to inject additional parameters into the request.
This is largely the same vulnerability as was recently found in undici by parrot409 -- I'm not affiliated with that researcher but want to give credit where credit is due! My PoC is largely based on their work.
The culprit is this line here: https://github.com/form-data/form-data/blob/426ba9ac440f95d1998dac9a5cd8d738043b048f/lib/form_data.js#L347
An attacker who is able to predict the output of Math.random() can predict this boundary value, and craft a payload that contains the boundary value, followed by another, fully attacker-controlled field. This is roughly equivalent to any sort of improper escaping vulnerability, with the caveat that the attacker must find a way to observe other Math.random() values generated by the application to solve for the state of the PRNG. However, Math.random() is used in all sorts of places that might be visible to an attacker (including by form-data itself, if the attacker can arrange for the vulnerable application to make a request to an attacker-controlled server using form-data, such as a user-controlled webhook -- the attacker could observe the boundary values from those requests to observe the Math.random() outputs). A common example would be a x-request-id header added by the server. These sorts of headers are often used for distributed tracing, to correlate errors across the frontend and backend. Math.random() is a fine place to get these sorts of IDs (in fact, opentelemetry uses Math.random for this purpose)
PoC here: https://github.com/benweissmann/CVE-2025-7783-poc
Instructions are in that repo. It's based on the PoC from https://hackerone.com/reports/2913312 but simplified somewhat; the vulnerable application has a more direct side-channel from which to observe Math.random() values (a separate endpoint that happens to include a randomly-generated request ID).
For an application to be vulnerable, it must:
form-data to send data including user-controlled data to some other system. The attacker must be able to do something malicious by adding extra parameters (that were not intended to be user-controlled) to this request. Depending on the target system's handling of repeated parameters, the attacker might be able to overwrite values in addition to appending values (some multipart form handlers deal with repeats by overwriting values instead of representing them as an array)If an application is vulnerable, this allows an attacker to make arbitrary requests to internal systems.