Out-of-bounds Read in Cesanta Mongoose
CVE-2026-73261
Mongoose is an embedded web server and network library. Prior to 7.23, the built-in TCP/IP stack enabled by MG_ENABLE_TCPIP in src/net_builtin.c does not reject a TCP option whose declared opts[1] length exceeds the remaining option bytes. In handle_opt(), a NOP followed by a truncated MSS option causes opts[3] to be read outside the declared options area and used as the low byte of dmss. An unauthenticated remote peer can corrupt the per-connection MSS value so later mg_send() calls transmit truncated or zero-length application payloads while the TCP connection otherwise appears healthy. This issue is fixed in version 7.23.
Vulnerability class: Drupalgeddon 2 (CVE-2018-7600)
Published .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
- Cesanta Mongoose — versions < 7.23
Weakness classification (CWE)
References
Frequently asked questions
- What is CVE-2026-73261?
- CVE-2026-73261 is a high-severity vulnerability in Cesanta Mongoose, classified under Improper Input Validation. CVSS score: 7.5/10. Published 2026-10-14.
- How severe is CVE-2026-73261?
- High severity. CVSS v3 base score is 7.5 out of 10.