What is CVE-2020-25756?

CVE-2020-25756 is a critical-severity vulnerability in Cesanta Mongoose, classified under Buffer Copy without Checking Size of Input (Classic Buffer Overflow). CVSS score: 9.8/10. Published 2020-09-18.

How severe is CVE-2020-25756?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Buffer overflow in Cesanta Mongoose

CVE-2020-25756

A 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 header can exploit this bug. NOTE: a committer has stated "this will not happen in practice.

Vulnerability class: Buffer Overflow

Published 2020-09-18 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.016 (75.8th percentile), scored 2026-10-24.

Low probability of exploitation in the next 30 days, but still tracked. 76th percentile — 75.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.016 · newest: 0.016 · change: -0.000

Affected products

Cesanta Mongoose — versions 6.18

Weakness classification (CWE)

CWE-120 — Buffer Copy without Checking Size of Input (Classic Buffer Overflow)

References

github.com/cesanta/mongoose/issues/1135 (Patch, Third Party Advisory, Issue Tracking)

Frequently asked questions

What is CVE-2020-25756?: CVE-2020-25756 is a critical-severity vulnerability in Cesanta Mongoose, classified under Buffer Copy without Checking Size of Input (Classic Buffer Overflow). CVSS score: 9.8/10. Published 2020-09-18.
How severe is CVE-2020-25756?: Critical severity. CVSS v3 base score is 9.8 out of 10.