Low exploit reference

CVE-2026-2967 — Cesanta Mongoose TCP Sequence Number net_builtin.c getpeer verification of source

A security vulnerability has been detected in Cesanta Mongoose up to 7.20. This affects the function getpeer of the file /src/net_builtin.c of the component TCP Sequence Number Handler. The manipulation leads to improper verification of source of a communication channel. The attack may be initiated remotely. The attack's complexity is rated as high. The exploitability is reported as difficult. The exploit has been disclosed publicly and may be used. The vendor was contacted early about this disclosure but did not respond in any way.

Published Feb 23, 2026 · Updated Oct 13, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: VulDB

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

EPSS 0.7% (30-day exploitation probability)+8
CISA SSVC: exploitation "poc"+5

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

0.72%

ahead of 53% of scored CVEs · Oct 14, 2026

Affects

Cesanta

Mongoose

CVSS base

3.7

Low · 2 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation

Proof of concept

none · proof-of-concept · active

Automatable

can an attacker script the kill-chain steps

Technical impact

Partial

partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Cesanta Mongoose).
The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
No fix documented in the sources: reduce exposure and monitor the vendor advisory.
Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Cesanta	Mongoose	version 7.10version 7.20version 7.19version 7.18version 7.17version 7.16version 7.15version 7.14 and 13 more version 7.13version 7.12version 7.11version 7.9version 7.8version 7.7version 7.6version 7.5version 7.4version 7.3version 7.2version 7.1version 7.0	Vulnerable	CVE Program (cve.org) e CISA ADP
Cesanta	Mongoose	≤ 7.20	Vulnerable	NIST National Vulnerability Database

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Network

Attack complexity

High

Privileges required

None

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

Low

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Scored by
6.3	CVSS 4.0	Medium	—	—	VulDB via CVE Program (cve.org) e CISA ADP
2.9	CVSS 4.0	Low	—	—	cna@vuldb.com via NIST National Vulnerability Database
3.7	CVSS 3.1	Low	2.2	1.4	cna@vuldb.com via NIST National Vulnerability Database
3.7	CVSS 3.1	Low	—	—	VulDB via CVE Program (cve.org) e CISA ADP
3.7	CVSS 3.0	Low	—	—	VulDB via CVE Program (cve.org) e CISA ADP
2.6	CVSS 2.0	Low	4.9	2.9	cna@vuldb.com via NIST National Vulnerability Database
2.6	CVSS 2.0	Low	—	—	VulDB via CVE Program (cve.org) e CISA ADP

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L (score shown at the top: cna@vuldb.com)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-940

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.72%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).

web/proxy/WAF logsnetwork IDS/IPS

Timeline

What happened to this CVE, newest first.

2026
Affected products added · cesanta/mongoose
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
SSVC assessment updated
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 13, 2026
CVSS changed · 3.7
Oct 13, 2026 · NIST National Vulnerability Database
Source status changed · → Analyzed
Oct 13, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 13, 2026 · NIST National Vulnerability Database
CVE published
Feb 23, 2026 · VulDB

Source activity

Repeated readings are counted rather than listed.

1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

5 on the record

github.com/dwBruijn/CVEs/blob/main/Mongoose/tcp_rst.md
Exploit, Third Party Advisory, related, NIST National Vulnerability Database
vuldb.com/
Third Party Advisory, VDB Entry, third-party-advisory, NIST National Vulnerability Database
vuldb.com/
Third Party Advisory, VDB Entry, vdb-entry, technical-description, NIST National Vulnerability Database
vuldb.com/
Permissions Required, VDB Entry, signature, permissions-required, NIST National Vulnerability Database
github.com/dwBruijn/CVEs/blob/main/Mongoose/tcp_rst.md
Exploit, Third Party Advisory, exploit, NIST National Vulnerability Database

Elsewhere on this site

Cesanta
every CVE for this vendor

CWE-940
other pages naming this weakness

Related CVEs (same products)

High CVE-2026-73252 Mongoose: Unauthenticated remote heap out-of-bounds read in built-in TLS: off-by-one length check in mg_tls_recv_record() underflows recv_len to SIZE_MAX 1d
High CVE-2026-73260 Mongoose: Out-of-bounds Read via length-counter underflow in built-in TLS X.509 DER parser 1d
High CVE-2026-73261 Mongoose: handle_opt() missing opts[1] > len check — 1-byte OOB read corrupts TCP MSS, silences mg_send() per connection 1d
High CVE-2026-63626 Mongoose: ppp_handle_ipv6cp() uses attacker-controlled length without bounds check — OOB read and heap overflow (PPP/PPPoE, MG_ENABLE_IPV6) 1d
High CVE-2026-6985 Cesanta Mongoose TCP Option net_builtin.c handle_opt infinite loop Apr 25, 2026
Low CVE-2026-6986 Cesanta Mongoose GCM Authentication Tag tls_aes128.c mg_aes_gcm_decrypt signature verification Apr 25, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No fixed version, patch or mitigation documented.
No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-2967 is "Cesanta Mongoose TCP Sequence Number net_builtin.c getpeer verification of source", rated Low. It affects Mongoose (Cesanta); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 3.7 describes technical severity. EPSS 0.72% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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