CWE-295 Base Draft

Improper Certificate Validation

This vulnerability occurs when an application fails to properly verify the authenticity of a digital certificate, or performs the verification incorrectly, allowing untrusted connections to appear…

Definition

What is CWE-295?

This vulnerability occurs when an application fails to properly verify the authenticity of a digital certificate, or performs the verification incorrectly, allowing untrusted connections to appear legitimate.
Digital certificates act like digital passports for servers and services, proving their identity. When an application doesn't rigorously check these certificates—for example, by accepting self-signed certificates, ignoring expiration dates, or not validating the certificate chain back to a trusted root—it can mistakenly connect to a malicious server impersonating a legitimate one. This creates a critical opening for man-in-the-middle (MitM) attacks where attackers can intercept, read, or modify sensitive data in transit. To prevent this, developers must ensure their code enforces strict certificate validation. This means always verifying the certificate's signature chain against a trusted root certificate authority (CA), checking the hostname matches, and ensuring the certificate is valid and not revoked. Relying on default settings is often insufficient; explicit configuration in libraries for TLS/SSL connections is typically required to reject invalid certificates and maintain a secure communication channel.
Vulnerability Diagram CWE-295
Improper Certificate Validation Client verify=false MITM attacker presents fake cert CN: bank.com (not signed) decrypts + relays traffic bank.com real server Disabled or weak cert validation lets an attacker terminate TLS.
Real-world impact

Real-world CVEs caused by CWE-295

  • CVE-2019-12496

    A Go framework for robotics, drones, and IoT devices skips verification of root CA certificates by default.

  • CVE-2014-1266

    chain: incorrect "goto" in Apple SSL product bypasses certificate validation, allowing Adversary-in-the-Middle (AITM) attack (Apple "goto fail" bug). CWE-705 (Incorrect Control Flow Scoping) -> CWE-561 (Dead Code) -> CWE-295 (Improper Certificate Validation) -> CWE-393 (Return of Wrong Status Code) -> CWE-300 (Channel Accessible by Non-Endpoint).

  • CVE-2021-22909

    Chain: router's firmware update procedure uses curl with "-k" (insecure) option that disables certificate validation (CWE-295), allowing adversary-in-the-middle (AITM) compromise with a malicious firmware image (CWE-494).

  • CVE-2008-4989

    Verification function trusts certificate chains in which the last certificate is self-signed.

  • CVE-2012-5821

    Web browser uses a TLS-related function incorrectly, preventing it from verifying that a server's certificate is signed by a trusted certification authority (CA)

  • CVE-2009-3046

    Web browser does not check if any intermediate certificates are revoked.

  • CVE-2011-0199

    Operating system does not check Certificate Revocation List (CRL) in some cases, allowing spoofing using a revoked certificate.

  • CVE-2012-5810

    Mobile banking application does not verify hostname, leading to financial loss.

How attackers exploit it

Step-by-step attacker path

  1. 1

    This code checks the certificate of a connected peer.

  2. 2

    In this case, because the certificate is self-signed, there was no external authority that could prove the identity of the host. The program could be communicating with a different system that is spoofing the host, e.g. by poisoning the DNS cache or using an Adversary-in-the-Middle (AITM) attack to modify the traffic from server to client.

  3. 3

    The following OpenSSL code obtains a certificate and verifies it.

  4. 4

    Even though the "verify" step returns X509_V_OK, this step does not include checking the Common Name against the name of the host. That is, there is no guarantee that the certificate is for the desired host. The SSL connection could have been established with a malicious host that provided a valid certificate.

  5. 5

    The following OpenSSL code ensures that there is a certificate and allows the use of expired certificates.

Vulnerable code example

Vulnerable C

This code checks the certificate of a connected peer.

Vulnerable C 
if ((cert = SSL_get_peer_certificate(ssl)) && host)
  	foo=SSL_get_verify_result(ssl);
  if ((X509_V_OK==foo) || X509_V_ERR_SELF_SIGNED_CERT_IN_CHAIN==foo))
```
// certificate looks good, host can be trusted*
Secure code example

Secure pseudo

Secure pseudo 
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
  const safe = validateAndEscape(input);
  return executeWithGuards(safe);
}
What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Prevention checklist

How to prevent CWE-295

  • Architecture and Design / Implementation Certificates should be carefully managed and checked to assure that data are encrypted with the intended owner's public key.
  • Implementation If certificate pinning is being used, ensure that all relevant properties of the certificate are fully validated before the certificate is pinned, including the hostname.
Detection signals

How to detect CWE-295

Automated Static Analysis - Binary or Bytecode SOAR Partial

According to SOAR [REF-1479], the following detection techniques may be useful: ``` Cost effective for partial coverage: ``` Bytecode Weakness Analysis - including disassembler + source code weakness analysis Binary Weakness Analysis - including disassembler + source code weakness analysis

Manual Static Analysis - Binary or Bytecode SOAR Partial

According to SOAR [REF-1479], the following detection techniques may be useful: ``` Cost effective for partial coverage: ``` Binary / Bytecode disassembler - then use manual analysis for vulnerabilities & anomalies

Dynamic Analysis with Automated Results Interpretation SOAR Partial

According to SOAR [REF-1479], the following detection techniques may be useful: ``` Cost effective for partial coverage: ``` Web Application Scanner

Dynamic Analysis with Manual Results Interpretation High

According to SOAR [REF-1479], the following detection techniques may be useful: ``` Highly cost effective: ``` Man-in-the-middle attack tool

Manual Static Analysis - Source Code High

According to SOAR [REF-1479], the following detection techniques may be useful: ``` Highly cost effective: ``` Focused Manual Spotcheck - Focused manual analysis of source Manual Source Code Review (not inspections)

Automated Static Analysis - Source Code SOAR Partial

According to SOAR [REF-1479], the following detection techniques may be useful: ``` Cost effective for partial coverage: ``` Source code Weakness Analyzer Context-configured Source Code Weakness Analyzer

Plexicus auto-fix

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Frequently asked questions

Frequently asked questions

What is CWE-295?

This vulnerability occurs when an application fails to properly verify the authenticity of a digital certificate, or performs the verification incorrectly, allowing untrusted connections to appear legitimate.

How serious is CWE-295?

MITRE has not published a likelihood-of-exploit rating for this weakness. Treat it as medium-impact until your threat model proves otherwise.

What languages or platforms are affected by CWE-295?

MITRE lists the following affected platforms: Mobile.

How can I prevent CWE-295?

Certificates should be carefully managed and checked to assure that data are encrypted with the intended owner's public key. If certificate pinning is being used, ensure that all relevant properties of the certificate are fully validated before the certificate is pinned, including the hostname.

How does Plexicus detect and fix CWE-295?

Plexicus's SAST engine matches the data-flow signature for CWE-295 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.

Where can I learn more about CWE-295?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/295.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-295

CWE-287 Parent

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Resources

Further reading

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