CVE-2026-11404Network attack vector

Remote service crash via ClientHello session ID

Published Jul 9, 2026 · Updated Jul 9, 2026

Out-of-bounds read in Cesanta Mongoose before 7.22 allows remote attackers to crash built-in TLS services with a crafted ClientHello. The mg_tls_server_recv_hello() parser uses the untrusted session_id_len byte to index cipher-suite and extension fields before confirming those offsets remain inside the received ClientHello. Exposure requires a server built with MG_TLS_BUILTIN; one oversized session ID length can terminate HTTPS, MQTTS, or WSS service availability without authentication.

CVSS severity8.7
High
EPSS probability0.61%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds read in Cesanta Mongoose before 7.22 allows remote attackers to crash built-in TLS services with a crafted ClientHello. The mg_tls_server_recv_hello() parser uses the untrusted session_id_len byte to index cipher-suite and extension fields before confirming those offsets remain inside the received ClientHello. Exposure requires a server built with MG_TLS_BUILTIN; one oversized session ID length can terminate HTTPS, MQTTS, or WSS service availability without authentication.

The record

CVE
CVE-2026-11404
Published
Jul 9, 2026
Updated
Jul 9, 2026
Vendor
Cesanta
Product
Mongoose
Classifications
CWE-125, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 9, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 9, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <7.22

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Cesanta · Mongooseversion=0 <7.22

Published CVSS scores

8.7VulnCheckCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
7.5VulnCheckCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-125Out-of-bounds Read
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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