Vulnerability · Published Aug 20, 2026 · Assigned by GitHub_M

CVE-2026-73259Mongoose: Reflected XSS via decoded URI in directory listing render

Medium 5.4

In plain English

A medium-severity cross-site scripting in mongoose from cesanta. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 35% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.4Medium

Exploit odds (30 days)0.4%top 64.7% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:14	mongoose	7.22+ds-1	DEBIAN-CVE-2026-73259
Ubuntu:26.10	mongoose	no fix listed	UBUNTU-CVE-2026-73259

Affected products (as reported)

Vendor	Product	Versions
cesanta	mongoose	< 7.22

Weakness: CWE-79 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N

References

https://github.com/cesanta/mongoose/security/advisories/GHSA-9cwm-487w-h25w x_refsource_CONFIRM
https://github.com/cesanta/mongoose/pull/3611 x_refsource_MISC
https://github.com/cesanta/mongoose/commit/a9df523f76f43a38bd53b4232b9cfd4c16869e71 x_refsource_MISC
https://github.com/cesanta/mongoose/releases/tag/7.22 x_refsource_MISC