CVE-2026-42765

Analyzed Analyzed - Analysis Complete

NULL Pointer Dereference in OpenSSL with OCSP Partial Chain Verification

Publication date: 2026-06-09

Last updated on: 2026-06-15

Assigner: OpenSSL Software Foundation

Description

Issue summary: When a partial-chain certificate verification is enabled together with OCSP response checking for the whole chain, a NULL dereference will happen if the verified chain does not have a self-signed trusted anchor, crashing the process. Impact summary: A NULL pointer dereference can trigger a crash which leads to a Denial of Service for an application. When performing OCSP response checking for certificates in the verification chain, the code always tries to access the next certificate as the issuer. There is a check for a self-signed certificate. However with the partial chain verification enabled when the chain does not have a self-signed trusted anchor, the issuer will be NULL for the last certificate in the chain. A NULL pointer dereference then happens. This issue affects only applications which enable both OCSP verification of the certificate chain (X509_V_FLAG_OCSP_RESP_CHECK_ALL) and partial chain verification (X509_V_FLAG_PARTIAL_CHAIN) in the certificate verification. Both flags are disabled by default. For that reason, we have assigned Low severity to the issue. No FIPS modules are affected by this issue as the affected code is outside the OpenSSL FIPS module boundary.

CVSS Scores

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Meta Information

Published

2026-06-09

Last Modified

2026-06-15

Generated

2026-06-30

AI Q&A

2026-06-09

EPSS Evaluated

2026-06-28

NVD

CVE-2026-42765

EUVD

EUVD-2026-35482

Affected Vendors & Products

Vendor	Product	Version / Range
openssl	openssl	From 3.6.0 (inc) to 3.6.3 (exc)
openssl	openssl	4.0.0

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-476	The product dereferences a pointer that it expects to be valid but is NULL.

Attack-Flow Graph

Executive Summary

This vulnerability occurs when an application enables both partial-chain certificate verification and OCSP response checking for the entire certificate chain. If the verified chain does not include a self-signed trusted anchor certificate, the process attempts to access a NULL issuer certificate, causing a NULL pointer dereference and crashing the process.

Specifically, during OCSP response checking, the code tries to access the next certificate as the issuer. Although there is a check for a self-signed certificate, with partial chain verification enabled and no self-signed trusted anchor present, the issuer pointer becomes NULL for the last certificate, leading to the crash.

Impact Analysis

The vulnerability can cause a NULL pointer dereference that triggers a crash of the application performing certificate verification. This results in a Denial of Service (DoS), making the application unavailable or unstable.

Mitigation Strategies

To mitigate this vulnerability, ensure that applications do not enable both OCSP verification of the certificate chain (X509_V_FLAG_OCSP_RESP_CHECK_ALL) and partial chain verification (X509_V_FLAG_PARTIAL_CHAIN) simultaneously, as both flags are disabled by default.

If your application requires these features, consider disabling partial chain verification or OCSP response checking until a patch or update addressing this issue is available.

Additionally, monitor for application crashes that may indicate a NULL pointer dereference caused by this issue.

Detection Guidance

This vulnerability occurs only in applications that explicitly enable both OCSP verification of the certificate chain (using the X509_V_FLAG_OCSP_RESP_CHECK_ALL flag) and partial chain verification (using the X509_V_FLAG_PARTIAL_CHAIN flag). Both flags are disabled by default.

Detection involves verifying whether your OpenSSL-based applications or services are configured to enable these two flags simultaneously. Since the issue causes a NULL pointer dereference leading to a crash (Denial of Service), monitoring application logs for crashes related to certificate verification or OCSP checks can help identify the problem.

There are no specific commands provided in the available resources or CVE description to detect this vulnerability directly on your network or system.

Compliance Impact

This vulnerability causes a denial of service by crashing the application due to a NULL pointer dereference when certain certificate verification flags are enabled.

However, there is no information provided about its direct impact on compliance with common standards and regulations such as GDPR or HIPAA.

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