CVE-2021-1799 in Safari
Summary
by MITRE • 04/03/2021
A port redirection issue was addressed with additional port validation. This issue is fixed in macOS Big Sur 11.2, Security Update 2021-001 Catalina, Security Update 2021-001 Mojave, tvOS 14.4, watchOS 7.3, iOS 14.4 and iPadOS 14.4, Safari 14.0.3. A malicious website may be able to access restricted ports on arbitrary servers.
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Analysis
by VulDB Data Team • 07/09/2025
This vulnerability represents a critical port redirection issue that existed in multiple Apple operating systems including macOS Big Sur, iOS, and related platforms. The flaw stems from insufficient validation of port numbers during network redirection operations, creating a pathway for malicious actors to bypass normal security boundaries. The vulnerability allows an attacker to redirect network traffic to restricted ports on arbitrary servers, effectively circumventing the normal port access controls that typically prevent unauthorized access to system resources. This type of issue falls under the CWE-645 category of "Invalid or Uninitialized State" and can be categorized as a network-level privilege escalation vulnerability within the ATT&CK framework under the T1071.004 technique for application layer protocol: DNS. The affected systems include iOS 14.4, iPadOS 14.4, macOS Big Sur 11.2, tvOS 14.4, watchOS 7.3, and the corresponding security updates for Catalina and Mojave. The security implications extend beyond simple port access as this vulnerability could enable attackers to probe internal networks, access sensitive services, or potentially exploit other vulnerabilities on systems that are normally protected by port restrictions.
The technical implementation of this vulnerability involves the manipulation of network redirection mechanisms within Apple's operating systems. When a web browser or application attempts to redirect network traffic to a specific port, the validation process failed to properly check whether the destination port was within acceptable ranges or if the redirection was being directed to system-protected ports. This validation gap allows attackers to craft malicious web pages that redirect traffic to ports that would normally be restricted or protected by the operating system's network security policies. The attack vector typically involves a malicious website that loads content designed to redirect network connections through the vulnerable redirection mechanism. This type of vulnerability is particularly dangerous because it can be exploited through standard web browsing activities without requiring any special privileges or user interaction beyond visiting a compromised website. The impact is significant as it could allow an attacker to access services that are normally restricted to localhost or other protected network zones, potentially leading to unauthorized access to system administration tools, databases, or other sensitive services that are typically protected by port-level access controls.
The operational impact of this vulnerability extends beyond immediate exploitation as it represents a fundamental flaw in the network security architecture of affected platforms. Organizations using these operating systems face potential exposure to attacks that could compromise internal network resources, especially in environments where network segmentation relies on port-based restrictions. The vulnerability could enable attackers to perform reconnaissance activities by scanning internal ports that would normally be inaccessible, potentially revealing the presence of additional services or vulnerabilities within the network. System administrators should be particularly concerned about the potential for this vulnerability to be used in combination with other attack vectors, as the ability to access restricted ports opens up possibilities for more sophisticated attacks. The vulnerability also affects web-based applications and services that rely on Apple platforms for their operation, potentially creating supply chain risks for organizations that depend on these systems for their network infrastructure. Given that the vulnerability affects widely deployed platforms including mobile operating systems, the potential attack surface is extensive and could be exploited by threat actors targeting various types of organizations.
Mitigation strategies for this vulnerability require immediate application of the security updates provided by Apple, which include the Security Update 2021-001 for macOS Catalina and Mojave, along with the respective system updates for iOS, iPadOS, tvOS, and watchOS. Organizations should prioritize deployment of these updates across all affected systems to ensure protection against exploitation attempts. Network administrators should also consider implementing additional monitoring for unusual network traffic patterns that might indicate exploitation attempts, particularly around port redirection activities. The vulnerability highlights the importance of proper input validation and the need for comprehensive security testing of network redirection mechanisms within operating systems. Security teams should conduct vulnerability assessments to identify systems that may still be running vulnerable versions of the affected platforms. Additional defensive measures include implementing web filtering solutions that can block access to known malicious domains and monitoring for suspicious network behavior that could indicate exploitation attempts. The incident also underscores the importance of maintaining up-to-date security patches and the need for organizations to establish robust patch management processes to protect against similar vulnerabilities in the future. Regular security audits should include verification of port access controls and network segmentation policies to ensure that proper protections remain in place.