Buffer Overflow in SwiftNIO SSL Certificate SANs Handling

Executive Summary

This vulnerability involves an out-of-bounds memory access in the swift-nio-ssl library. The issue occurs when accessing raw bytes of Subject Alternative Names (SANs) in certificates through the NIOSSLCertificate._subjectAlternativeNames API. The library incorrectly assumes all SANs are backed by ASN1_STRING, but some SAN types use different structures, leading to memory corruption when their buffers are accessed.

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Detection Guidance

To detect this vulnerability, check if your system uses swift-nio-ssl versions 2.18.0 to 2.37.1. Run: swift package show-dependencies --format json | grep swift-nio-ssl. If the version is within the affected range, update to version 2.37.2 or later.

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Impact Analysis

This vulnerability primarily affects users who directly access the byte views of SANs via the underscored API without proper type safety checks. It can lead to out-of-bounds memory reads, potentially causing crashes or undefined behavior in applications using vulnerable versions of swift-nio-ssl (2.18.0 to 2.37.1).

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Mitigation Strategies

Immediately update swift-nio-ssl to version 2.37.2 or later. Avoid using the underscored API NIOSSLCertificate._subjectAlternativeNames directly without type safety checks.

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