CWE-297 Variant Incomplete High likelihood

Improper Validation of Certificate with Host Mismatch

This vulnerability occurs when an application accepts a valid SSL/TLS certificate without properly verifying that it actually belongs to the specific host it's connecting to. Even a correctly signed…

Definition

What is CWE-297?

This vulnerability occurs when an application accepts a valid SSL/TLS certificate without properly verifying that it actually belongs to the specific host it's connecting to. Even a correctly signed certificate from a trusted authority can be misused if the hostname check is missing or flawed.
When your application connects to a server, it must verify that the certificate presented matches the intended hostname. This is done by checking the Common Name (CN) or, more reliably, the Subject Alternative Name (SAN) fields in the certificate. If this validation is skipped or implemented incorrectly, an attacker with a valid certificate for a different domain can impersonate your trusted service, leading to man-in-the-middle attacks and data interception. Common validation pitfalls include incomplete string comparisons that can be tricked by special characters, or failing to perform hostname checks when using certificate pinning. Always validate the hostname at the time of pinning and use established library functions for hostname verification instead of custom string matching, as these functions correctly handle edge cases like null bytes and wildcards.
Real-world impact

Real-world CVEs caused by CWE-297

  • CVE-2012-5810

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

  • CVE-2012-5811

    Mobile application for printing documents does not verify hostname, allowing attackers to read sensitive documents.

  • CVE-2012-5807

    Software for electronic checking does not verify hostname, leading to financial loss.

  • CVE-2012-3446

    Cloud-support library written in Python uses incorrect regular expression when matching hostname.

  • CVE-2009-2408

    Web browser does not correctly handle '\0' character (NUL) in Common Name, allowing spoofing of https sites.

  • CVE-2012-0867

    Database program truncates the Common Name during hostname verification, allowing spoofing.

  • CVE-2010-2074

    Incorrect handling of '\0' character (NUL) in hostname verification allows spoofing.

  • CVE-2009-4565

    Mail server's incorrect handling of '\0' character (NUL) in hostname verification allows spoofing.

How attackers exploit it

Step-by-step attacker path

  1. 1

    Identify a code path that handles untrusted input without validation.

  2. 2

    Craft a payload that exercises the unsafe behavior — injection, traversal, overflow, or logic abuse.

  3. 3

    Deliver the payload through a normal request and observe the application's reaction.

  4. 4

    Iterate until the response leaks data, executes attacker code, or escalates privileges.

Vulnerable code example

Vulnerable C

The following OpenSSL code obtains a certificate and verifies it.

Vulnerable C 
cert = SSL_get_peer_certificate(ssl);
  if (cert && (SSL_get_verify_result(ssl)==X509_V_OK)) {
```
// do secret things* 
  		}
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-297

  • Architecture and Design Fully check the hostname of the certificate and provide the user with adequate information about the nature of the problem and how to proceed.
  • 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-297

Automated Static Analysis High

Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

Dynamic Analysis with Manual Results Interpretation

Set up an untrusted endpoint (e.g. a server) with which the product will connect. Create a test certificate that uses an invalid hostname but is signed by a trusted CA and provide this certificate from the untrusted endpoint. If the product performs any operations instead of disconnecting and reporting an error, then this indicates that the hostname is not being checked and the test certificate has been accepted.

Black Box

When Certificate Pinning is being used in a mobile application, consider using a tool such as Spinner [REF-955]. This methodology might be extensible to other technologies.

Plexicus auto-fix

Plexicus auto-detects CWE-297 and opens a fix PR in under 60 seconds.

Codex Remedium scans every commit, identifies this exact weakness, and ships a reviewer-ready pull request with the patch. No tickets. No hand-offs.

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Frequently asked questions

Frequently asked questions

What is CWE-297?

This vulnerability occurs when an application accepts a valid SSL/TLS certificate without properly verifying that it actually belongs to the specific host it's connecting to. Even a correctly signed certificate from a trusted authority can be misused if the hostname check is missing or flawed.

How serious is CWE-297?

MITRE rates the likelihood of exploit as High — this weakness is actively exploited in the wild and should be prioritized for remediation.

What languages or platforms are affected by CWE-297?

MITRE lists the following affected platforms: Mobile, Not Technology-Specific.

How can I prevent CWE-297?

Fully check the hostname of the certificate and provide the user with adequate information about the nature of the problem and how to proceed. 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-297?

Plexicus's SAST engine matches the data-flow signature for CWE-297 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-297?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/297.html. You can also reference OWASP and NIST documentation for adjacent guidance.

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Weaknesses related to CWE-297

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Further reading

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