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CVE Record

CVE-2020-36477: An issue was discovered in Mbed TLS before 2.24.0.

An issue was discovered in Mbed TLS before 2.24.0. The verification of X.509 certificates when matching the expected common name (the cn argument of mbedtls_x509_crt_verify) with the actual certificate name is mishandled: when the subjecAltName extension is present, the expected name is compared to any name in that extension regardless of its type. This means that an attacker could impersonate a 4-byte or 16-byte domain by getting a certificate for the corresponding IPv4 or IPv6 address (this would require the attacker to control that IP address, though).

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

Mbed TLS could accept the wrong kind of certificate identity when checking a peer name. In narrow cases, an attacker controlling an IP address could obtain a certificate for that address and impersonate a matching 4-byte or 16-byte domain name.

Executive priority

Treat this as a targeted TLS trust issue, not a broad remote-code-execution emergency. Prioritize systems that use older Mbed TLS in exposed clients, gateways, embedded devices, or security-sensitive communications.

Technical view

Before Mbed TLS 2.24.0, mbedtls_x509_crt_verify mishandled expected common-name matching when subjectAltName was present, comparing the expected name against any SAN entry regardless of type. The source describes possible impersonation of 4-byte or 16-byte domains via IPv4 or IPv6 SANs.

Likely exposure

Exposure is most likely in products, services, or firmware using Mbed TLS before 2.24.0 for X.509 certificate verification. Risk depends on whether the application validates peer names through mbedtls_x509_crt_verify and could encounter the described short-domain edge case.

Exploitation context

The CVE record does not report active exploitation, and it is not listed as KEV in the supplied bundle. Exploitation is conditional because the attacker would need control of the corresponding IPv4 or IPv6 address and a certificate for it.

Researcher notes

The key condition is SAN type confusion during expected-name comparison. The public description is specific but limited: it names the affected API behavior and version boundary, but provides no CVSS, CWE, exploit evidence, or broad product list.

Mitigation direction

  • Upgrade Mbed TLS to 2.24.0 or a later vendor-supported release.
  • Apply distribution or product vendor security updates where Mbed TLS is packaged downstream.
  • Inventory statically linked or bundled Mbed TLS copies in applications and firmware.
  • Check vendor guidance before relying on configuration-only mitigations.

Validation and detection

  • Confirm deployed Mbed TLS versions are not earlier than 2.24.0.
  • Review SBOMs and build manifests for bundled Mbed TLS dependencies.
  • Identify code paths using mbedtls_x509_crt_verify for peer-name validation.
  • Run approved regression tests for certificate name and SAN type handling.
Prepared
Confidence
medium
Sources
5

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
0Timeline events
0ADP providers
4Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

No CWE listed

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