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Vulnerability record · CVE-2026-73259 · published 20 August 2026

CVE-2026-73259: Cesanta mongoose cross-site scripting vulnerability

Cesanta · Mongoose

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.

5.4 CVSS 3.1 Medium EPSS 0.41% · top 67.1% CWE-79 · Cross-site scripting
5.4CVSS 3.1 base score
0.41%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
5References, 2 tagged exploit
29 Sep 2026Last modified by NVD

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.

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/cesanta/mongoose/commit/a9df523f76f43a38bd53b4232b9cfd4c16869e71 Patch
https://github.com/cesanta/mongoose/pull/3611 Issue TrackingPatch
https://github.com/cesanta/mongoose/releases/tag/7.22 Release Notes
https://github.com/cesanta/mongoose/security/advisories/GHSA-9cwm-487w-h25w ExploitVendor Advisory
https://github.com/cesanta/mongoose/security/advisories/GHSA-9cwm-487w-h25w ExploitVendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.8CVE-2024-42383Cesanta mongoose vulnerabilityUse of Out-of-range Pointer Offset vulnerability in Cesanta Mongoose Web Server v7.14 allows to write a NULL byte value beyond the memory space dedic…EPSS 0.27%9.8CVE-2020-25756Cesanta mongoose classic buffer overflow vulnerabilityA buffer overflow vulnerability exists in the mg_get_http_header function in Cesanta Mongoose 6.18 due to a lack of bounds checking. A crafted HTTP h…EPSS 1.6%9.8CVE-2019-19307Cesanta mongoose out-of-bounds read vulnerabilityAn integer overflow in parse_mqtt in mongoose.c in Cesanta Mongoose 6.16 allows an attacker to achieve remote DoS (infinite loop), or possibly cause …EPSS 42%9.8CVE-2019-12951Cesanta mongoose out-of-bounds write vulnerabilityAn issue was discovered in Mongoose before 6.15. The parse_mqtt() function in mg_mqtt.c has a critical heap-based buffer overflow.EPSS 2.0%9.8CVE-2018-20355Cesanta mongoose use after free vulnerabilityAn invalid write of 8 bytes due to a use-after-free vulnerability in the mg_http_free_proto_data_cgi function call in mongoose.c in Cesanta Mongoose …EPSS 3.6%9.8CVE-2018-20353Cesanta mongoose use after free vulnerabilityAn invalid read of 8 bytes due to a use-after-free vulnerability during a "NULL test" in the mg_http_get_proto_data function in mongoose.c in Cesanta…EPSS 3.6%9.8CVE-2018-20356Cesanta mongoose use after free vulnerabilityAn invalid read of 8 bytes due to a use-after-free vulnerability in the mg_http_free_proto_data_cgi function call in mongoose.c in Cesanta Mongoose E…EPSS 3.6%9.8CVE-2018-20354Cesanta mongoose use after free vulnerabilityAn invalid read of 8 bytes due to a use-after-free vulnerability during a "return" in the mg_http_get_proto_data function in mongoose.c in Cesanta Mo…EPSS 3.6%

Source: NIST National Vulnerability Database (record CVE-2026-73259), CISA KEV, FIRST EPSS (scores of 2026-10-06). This page is refreshed as NVD updates the record.