---
id: CVE-2026-43820
title: >-
  NIOSSLCertificate._subjectAlternativeNames provides access to the raw bytes
  for a cert's SANs
summary: >-
  NIOSSLCertificate._subjectAlternativeNames provides access to the raw bytes
  for a cert's SANs. NIOSSL provides access to a buffer assumed to be backed by
  an ASN1_STRING, but not all SANs are backed by ASN1_STRING, so accessing the
  buffer…
severity: high
cvss: 7.7
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H'
cwe:
  - CWE-125
vendor: apple
product: swiftnio_ssl
affected:
  - 'swiftnio_ssl >= 2.18.0, < 2.37.2'
patched:
  - swiftnio_ssl 2.37.2
published: '2026-07-23'
updated: '2026-09-04'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-43820'
references:
  - url: >-
      https://github.com/apple/swift-nio-ssl/security/advisories/GHSA-xfxg-9975-pc2j
    label: product-security@apple.com
  - url: >-
      https://github.com/apple/swift-nio-ssl/security/advisories/GHSA-xfxg-9975-pc2j
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
tags:
  - nvd
epss: 0.00109
epssPercentile: 0.01116
ingestedAt: '2026-09-05T13:39:55.855Z'
---

## Overview

NIOSSLCertificate._subjectAlternativeNames provides access to the raw bytes for a cert's SANs. NIOSSL provides access to a buffer assumed to be backed by an ASN1_STRING, but not all SANs are backed by ASN1_STRING, so accessing the buffer for such a type can lead to out-of-bounds memory access. This vulnerability is addressed in swift-nio-ssl version 2.37.2.

## Affected

- `swiftnio_ssl >= 2.18.0, < 2.37.2`

## Remediation

Upgrade past the affected range:

- `swiftnio_ssl 2.37.2`