Vulnerability record · CVE-2026-6985 · published 25 April 2026

CVE-2026-6985: Cesanta mongoose improper resource shutdown vulnerability

Cesanta · Mongoose

A weakness has been identified in Cesanta Mongoose up to 7.20. This vulnerability affects the function handle_opt of the file /src/net_builtin.c of the component TCP Option Handler. This manipulation of the argument optlen causes infinite loop. The attack is possible to be carried out remotely. The exploit has been made available to the public and could be used for attacks. Upgrading to version 7.21 is able to resolve this issue. Upgrading the affected component is advised. VulDB has contacted the vendor early and they confirmed quickly, that this issue got fixed already.

5.5 CVSS 4.0 Medium EPSS 0.92% · top 40.8% CWE-404 · Improper resource shutdownCWE-835 · CWE-835

5.5CVSS 4.0 base score, v2 5.0

0.92%EPSS exploitation probability, 30 days

NoNot in CISA KEV

1Affected product versions listed by NVD

5References, 1 tagged exploit

17 Jun 2026Last modified by NVD

Description

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

Affected products

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

Mongoose Cesanta

References

Link	Tags
https://github.com/cesanta/mongoose/releases/tag/7.21	ProductRelease Notes
https://github.com/dwBruijn/CVEs/blob/main/Mongoose/TCP_opt_dos.md	ExploitThird Party Advisory
https://vuldb.com/submit/796230	Third Party AdvisoryVDB Entry
https://vuldb.com/vuln/359528	Third Party AdvisoryVDB Entry
https://vuldb.com/vuln/359528/cti	Permissions RequiredVDB Entry

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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%18 Nov 2024 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%18 Sep 2020 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%26 Nov 2019 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%24 Jun 2019 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%10 Jun 2019 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%10 Jun 2019 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%10 Jun 2019 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%10 Jun 2019

Source: NIST National Vulnerability Database (record CVE-2026-6985), CISA KEV, FIRST EPSS (scores of 2026-10-07). This page is refreshed as NVD updates the record.