CVE-2026-93493 in Netty
Summary
by MITRE • 09/18/2026
A flaw was found in Netty's `netty-handler-ssl-ocsp` component. A remote attacker can exploit this vulnerability by providing an Online Certificate Status Protocol (OCSP) response that omits the optional `nextUpdate` field. This omission causes the OCSP validation to be silently skipped, leading to applications proceeding with an unvalidated certificate. This can result in a bypass of security controls where certificate validation is expected.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 09/18/2026
The vulnerability identified within Netty's netty-handler-ssl-ocsp component represents a critical failure in cryptographic verification logic during the Online Certificate Status Protocol (OCSP) checking process. OCSP is an internet protocol used for obtaining the revocation status of an X.509 digital certificate, serving as a primary mechanism to ensure that certificates have not been revoked by their issuing authority prior to establishing secure connections. The flaw specifically arises when a remote attacker provides an OCSP response that omits the optional nextUpdate field. According to RFC 6960, which defines the syntax and semantics of OCSP responses, while this field is technically marked as optional in certain contexts, its absence creates ambiguity regarding the freshness and validity period of the revocation status information. In a secure implementation, missing or malformed temporal data should trigger an error state that halts validation to prevent potential misuse. However, due to the specific coding oversight in Netty's handler, the system interprets this omission not as an invalid response requiring rejection, but rather as a signal to skip the OCSP check entirely.
This silent skipping of certificate validation constitutes a severe security control bypass with significant operational implications for any application relying on mutual TLS or strict client authentication mechanisms that utilize OCSP stapling or direct OCSP queries. When the validation is skipped, the application proceeds under the false assumption that the peer's certificate has been verified against current revocation lists. Consequently, if an attacker possesses a valid but revoked certificate, such as one compromised through key theft or issued to a malicious entity before being flagged for revocation, they can successfully authenticate and establish encrypted sessions with vulnerable services. This undermines the fundamental trust model of public key infrastructure by allowing connections from entities that should be explicitly denied based on their current status in the Certificate Authority's records. The impact is particularly acute in environments where compliance frameworks mandate strict certificate validation to prevent unauthorized access or data exfiltration via compromised credentials.
From a classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation and CWE-345 Insufficient Verification of Data Authenticity. The root cause lies in the failure to properly validate the structural integrity and completeness of the OCSP response before proceeding with trust decisions. In terms of offensive security tactics, this flaw facilitates techniques associated with MITMATTACK::SPOOFING or CREDENTIAL_ACCESS if used in conjunction with other exploits to intercept traffic from systems that incorrectly believe they are communicating with a verified peer. The silent nature of the failure is particularly dangerous because it does not generate error logs or alerts that would typically alert administrators to an attempted attack, allowing malicious actors to operate undetected within the network perimeter for extended periods.
Mitigation strategies must focus on enforcing strict adherence to OCSP response standards and ensuring that any deviation from expected protocol behavior results in a failure state rather than a graceful degradation of security. For users of Netty, applying the latest patches provided by the maintainers is the primary remediation step, as these updates correct the logic error that permits the skipping of validation when nextUpdate fields are absent. In environments where immediate patching is not feasible, implementing network-level controls such as Web Application Firewalls or intrusion detection systems configured to monitor for anomalous TLS handshake patterns involving OCSP responses with missing temporal metadata can provide a layer of defense. Additionally, organizations should review their certificate pinning strategies and consider reducing reliance on OCSP by integrating Certificate Transparency logs into their validation pipelines, thereby adding an additional layer of verification that is less susceptible to this specific type of protocol-level ambiguity. Regular auditing of TLS configurations and ensuring that security libraries are kept up-to-date with the latest vulnerability fixes remain essential practices for maintaining robust cryptographic hygiene.