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CVE-2026-73251

Cesanta Mongoose vulnerability

9.1 CRITICALEPSS 0.19%
  1. Published20 Aug 2026

Description

Mongoose is an embedded web server and network library. Prior to 7.23, a network attacker can impersonate a TLS server to a Mongoose client configured with a multi-certificate CA bundle. In src/tls_builtin.c, the mg_tls_init() function stores the bundle in tls->ca_bundle_der while tls->ca_der.len remains zero, and mg_tls_recv_cert() uses tls_bundle_find() to accept a Common Name match without calling mg_tls_verify_cert_signature(). A forged self-signed certificate can therefore satisfy hostname and CertificateVerify checks and enable interception, credential disclosure, traffic modification, and malicious responses. This issue is fixed in version 7.23.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityNone
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Affected products

Cesanta Mongoose< 7.23

Remediation

Fixed in
Cesanta Mongoose≥ 7.23

References

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Frequently asked

Is CVE-2026-73251 being actively exploited?

CVE-2026-73251 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.19%.

How severe is CVE-2026-73251?

CVE-2026-73251 has a CVSS 3.1 base score of 9.1, rated critical. EPSS estimates a 0.19% probability of exploitation.

Which products are affected by CVE-2026-73251?

Affected products include Cesanta Mongoose.

How do I fix CVE-2026-73251?

Upgrade affected software to a fixed version, for example Cesanta Mongoose 7.23 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.