CVE-2026-73259 Mongoose: Reflected XSS via decoded URI in directory listing render
Attackers can execute scripts in victim browsers via crafted URLs in Mongoose directory listings, potentially stealing session data or performing actions.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-73259?
CVE-2026-73259 is a medium-severity cross-site scripting vulnerability in Cesanta Mongoose, published on 20 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
Mongoose is an embedded web server and network library. Prior to 7.22, a remote attacker can send a crafted percent-encoded request path to a deployment using MG_ENABLE_DIRLIST and persuade a user to visit it. The mg_http_serve_dir() and listdir() path in src/http.c places the decoded request URI into the title and h1 elements without HTML entity encoding. The resulting reflected cross-site scripting executes in the Mongoose origin and can expose session data or perform actions as the victim. This issue is fixed in version 7.22.
Weakness: CWE-79
Which versions are affected by CVE-2026-73259?
It affects 1 product.
Products include Cesanta Mongoose.
How do I fix CVE-2026-73259?
Upgrade to a fixed version.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-73259 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-73259 exists.
Other vulnerabilities in Cesanta Mongoose
Sources
Also known as DEBIAN-CVE-2026-73259, GHSA-9cwm-487w-h25w, JLSEC-2026-1383, UBUNTU-CVE-2026-73259.