CVE-2026-86881 in iOS
Summary
by MITRE • 09/15/2026
A certificate validation issue was addressed with improved certificate validation. This issue is fixed in iOS 26.7 and iPadOS 26.7, iOS 27 and iPadOS 27, macOS Golden Gate 27, macOS Sequoia 15.8, macOS Tahoe 26.7, tvOS 27, visionOS 27, watchOS 27. An attacker with a compromised intermediate certificate authority may be able to issue certificates with arbitrary extended key usages.
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Analysis
by VulDB Data Team • 09/15/2026
The vulnerability described involves a critical flaw in the certificate validation logic within Apple's operating systems, specifically affecting iOS, iPadOS, macOS, tvOS, visionOS, and watchOS versions prior to the specified updates. This security defect centers on how the system validates X.509 certificates issued by intermediate Certificate Authorities (CAs). In a standard Public Key Infrastructure (PKI) hierarchy, root CAs issue certificates to intermediate CAs, which in turn issue end-entity certificates for servers or applications. A fundamental principle of this chain is that an intermediate CA should only be permitted to sign certificates with specific extended key usages defined by the parent CA and industry standards such as RFC 5280. The flaw allows an attacker who has compromised a legitimate intermediate certificate authority to bypass these restrictions, enabling them to issue certificates with arbitrary extended key usages. This means the maliciously issued certificates can claim capabilities they were never authorized for, such as server authentication when only intended for code signing or client authentication.
From a technical perspective, this failure represents a breakdown in constraint propagation and validation within the certificate chain verification process. When an intermediate CA presents a certificate to be validated by the operating system's security framework, the system must verify that the extended key usage extensions present in the end-entity certificate are permitted by the constraints set on the issuing intermediate CA certificate. The vulnerability indicates that this check was either missing or insufficiently rigorous, allowing certificates with unrestricted or incorrectly assigned permissions to pass validation. This is a severe deviation from secure cryptographic practices because it undermines the trust model established by PKI. If an attacker can obtain control over even one intermediate CA key, they can impersonate any service or application on the network without triggering certificate warnings in browsers or system security dialogs.
The operational impact of this vulnerability is profound and aligns with several known attack vectors documented in industry frameworks. According to the Common Weakness Enumeration (CWE), this issue corresponds closely to CWE-295, Improper Certificate Validation, as well as CWE-780, Use of RSA Key for Operations Not Allowed by its Constraints. The ability to forge certificates with arbitrary extended key usages directly facilitates Man-in-the-Middle (MitM) attacks. An attacker positioned between a user and a legitimate service can present the forged certificate, which will be accepted as valid by the compromised device. This allows the interception of encrypted traffic, including sensitive data like login credentials, financial information, and private communications, without detection. Furthermore, this flaw impacts code signing integrity on macOS and iOS platforms. If an attacker can issue certificates with code-signing extensions, they could potentially sign malicious applications that appear legitimate to the operating system's security checks, facilitating malware distribution or unauthorized software execution.
This vulnerability also maps directly to tactics within the MITRE ATT&CK framework, particularly T1557, Adversary-in-the-Middle, and T1609, Software Deployment Tools, if leveraged for signing malicious binaries. The compromise of an intermediate CA is a high-impact event in cybersecurity because it cascades trust down to all entities relying on that CA. Unlike vulnerabilities requiring local access or user interaction, this flaw can be exploited remotely by any attacker who has successfully compromised the private key of an affected intermediate CA. This scenario highlights the critical importance of securing Certificate Authority infrastructure and ensuring strict adherence to RFC 5280 constraints during certificate issuance.
Mitigation for this vulnerability requires immediate action from both system administrators and end-users. The primary remediation is to apply the software updates provided by Apple, specifically iOS 26.7, iPadOS 26.7, iOS 27, iPadOS 27, macOS Golden Gate 27, macOS Sequoia 15.8, macOS Tahoe 26.7, tvOS 27, visionOS 27, and watchOS 27. These updates contain the necessary patches to enforce stricter validation of certificate extensions and constraints during the chain verification process. For organizations managing large fleets of devices, it is crucial to prioritize patching endpoints that handle sensitive data or connect to critical infrastructure. Additionally, Certificate Authorities must review their issuance policies to ensure that intermediate CAs are strictly limited in scope and that revocation mechanisms such as OCSP or CRLs are robustly implemented to detect compromised keys quickly. Security monitoring should also be enhanced to look for unusual certificate issuance patterns from internal CAs, which could indicate a breach leading up to the exploitation of this flaw.