XSS in Cesanta Mongoose
CVE-2026-73259
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.
Vulnerability class: XSS (Cross-Site Scripting)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N.
EPSS exploit prediction
EPSS: 0.004 (32.7th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 33rd percentile — 32.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.004 · change: +0.002
Affected products
- Cesanta Mongoose — versions < 7.22
Weakness classification (CWE)
References
- github.com/cesanta/mongoose/security/advisories/GHSA-9cwm-487w-h25w (Exploit, Vendor Advisory)
- github.com/cesanta/mongoose/pull/3611 (Patch, Issue Tracking)
- github.com/cesanta/mongoose/commit/a9df523f76f43a38bd53b4232b9cfd4c16869e71 (Patch)
- github.com/cesanta/mongoose/releases/tag/7.22 (Release Notes)
Frequently asked questions
- What is CVE-2026-73259?
- CVE-2026-73259 is a medium-severity vulnerability in Cesanta Mongoose, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2026-08-20.
- How severe is CVE-2026-73259?
- Medium severity. CVSS v3 base score is 5.4 out of 10.