OpenSSL OCSP Stapling Vulnerability Allows Remote Code Execution
A double free vulnerability in OpenSSL's OCSP Stapling verification (CVE-2026-35188) enables remote attackers to execute arbitrary code, though user interaction is required.
A critical vulnerability has been identified in OpenSSL's implementation of OCSP Stapling, a feature used to efficiently verify digital certificates. The flaw, tracked as CVE-2026-35188, is a double free vulnerability that could allow remote attackers to execute arbitrary code on affected systems.
The vulnerability arises from an issue within the processing of malformed OCSP responses. Specifically, the code fails to validate the existence of an object before attempting to free it multiple times. This double freeing of memory can lead to a corrupted state, which an attacker can then exploit to gain control of the program's execution flow.
Exploitation of this vulnerability is not straightforward and requires a degree of user interaction. An attacker must trick a user into making a request to a malicious server. Upon receiving a specially crafted OCSP response from this server, the vulnerability can be triggered, potentially leading to arbitrary code execution within the context of the vulnerable OpenSSL process.
Zero Day Initiative, which disclosed the vulnerability, has assigned it a CVSS score of 7.5, classifying it as high severity. While the requirement for user interaction and a malicious server limits its immediate widespread exploitability, the potential impact of remote code execution remains significant for any application or service relying on the vulnerable OpenSSL component.
OpenSSL has acknowledged the vulnerability and has released an update to address it. Users and administrators are strongly advised to update their OpenSSL installations to the patched version as soon as possible to mitigate the risk. The advisory from OpenSSL provides further details on the fix and the specific versions affected.
This vulnerability highlights the ongoing challenges in securing complex cryptographic libraries like OpenSSL. Even well-established and widely used software can harbor subtle memory management bugs that, when combined with specific attack vectors, can lead to severe security consequences. The disclosure timeline indicates a coordinated effort between the vulnerability researcher and OpenSSL to ensure a timely patch.
As OCSP Stapling is a common feature for improving TLS handshake performance and security, many web servers, clients, and other network-facing applications utilize it. Therefore, the impact of this vulnerability could be widespread across various internet infrastructure components. Prompt patching is crucial to prevent potential exploitation by malicious actors.