Overview
CVE-2025-11933 describes a vulnerability in wolfSSL version 5.8.2 and earlier, affecting multiple platforms. This vulnerability arises from improper input validation during the parsing of the TLS 1.3 CKS (Certificate Key Share) extension. A remote, unauthenticated attacker can exploit this flaw to potentially cause a denial-of-service (DoS) condition by sending a specially crafted ClientHello message containing duplicate CKS extensions.
Technical Details
The vulnerability resides in the way wolfSSL handles the CKS extension during the TLS 1.3 handshake. Specifically, the code fails to adequately check for and handle duplicate instances of the CKS extension within the ClientHello message. When an attacker sends a ClientHello with multiple CKS extensions, the parsing logic can enter a state where excessive resource consumption occurs, ultimately leading to a denial of service. The exact mechanism of resource exhaustion is implementation-specific but typically involves either excessive memory allocation, infinite loops, or repeated processing of the same data.
CVSS Analysis
Currently, the CVSS score and severity for CVE-2025-11933 are listed as N/A. This likely indicates that the vulnerability assessment is still pending or that the impact and exploitability have not been fully quantified. However, given the potential for remote, unauthenticated denial of service, it’s prudent to consider this vulnerability as having at least a moderate severity until a formal CVSS score is assigned.
Possible Impact
The successful exploitation of CVE-2025-11933 can result in a denial-of-service condition, rendering affected systems or services unavailable. This can impact applications relying on wolfSSL for secure communication, potentially disrupting critical functionalities. The lack of authentication requirement for exploitation increases the risk, as any attacker on the network can potentially trigger the vulnerability. The severity of the impact will depend on the specific application and the resources available to the attacker.
Mitigation or Patch Steps
The primary mitigation for CVE-2025-11933 is to upgrade to a patched version of wolfSSL. According to the provided information, a fix has been implemented in a pull request. Follow these steps:
- Upgrade wolfSSL: Update your wolfSSL library to the latest version, or a version that includes the fix from the pull request referenced below. Check the wolfSSL release notes for specific versions that address this vulnerability.
- Monitor Network Traffic: Implement network monitoring to detect suspicious ClientHello messages with excessive or malformed CKS extensions.
- Web Application Firewalls (WAFs): Consider using a WAF to filter out malicious TLS traffic. Configure rules to identify and block ClientHello messages with suspicious characteristics.
