CVE-2026-43820: NIOSSLCertificate._subjectAlternativeNames provides access to the raw bytes for a cert's SANs

Routine

HIGH 7.7UPGRADE

CVE-2026-43820 is a high-severity flaw (CVSS 7.7) affecting swiftnio ssl. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

High severity
Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	7.7 (High)
Attack vector	Local
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.1% (top 99%)
CISA exploited list	No
Weakness	CWE-125
Published	2026-07-23
Last modified	2026-10-24

Publisher (CNA): Apple Inc. · Vendor: apple

Last updated 2026-10-24 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-23 15:17 UTCPublished CVE record published
2026-10-24 13:10 UTCUpdated Record last modified

apple swiftnio ssl UPGRADE

Affected: >= 2.18.0 and < 2.37.2

Fixed in: 2.37.2

Safe to downgrade to: a release before 2.18.0

1. Check installed version

apt-cache policy swiftnio-ssl || rpm -q swiftnio-ssl || swiftnio-ssl --version

2. UPGRADE to 2.37.2 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade swiftnio-ssl

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade swiftnio-ssl

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 2.18.0 (Debian / Ubuntu)

apt-cache madison swiftnio-ssl sudo apt install swiftnio-ssl=<VERSION_BEFORE_2.18.0> sudo apt-mark hold swiftnio-ssl

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list swiftnio-ssl sudo dnf downgrade swiftnio-ssl-<VERSION_BEFORE_2.18.0> sudo dnf versionlock add swiftnio-ssl

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Exact fixes by distribution

Fedora 46 · sugar-clock · FIXED · 22.1-17.fc46 · FEDORA-2026-57948849df · source

sudo dnf upgrade --advisory=FEDORA-2026-57948849df

Fedora ELN · selinux-policy · FIXED · 45.23-1.eln159 · FEDORA-2026-3668c969a2 · source

sudo dnf upgrade --advisory=FEDORA-2026-3668c969a2

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Write-up: github.com/apple/swift-nio-ssl/security/advisories/GHSA-xfxg-9975-pc2j

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-43820?

swiftnio ssl: upgrade to 2.37.2. Exact commands for each OS are on this page.

Is CVE-2026-43820 being exploited?

CVE-2026-43820 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-43820 affect?

CVE-2026-43820 affects swiftnio ssl. Severity is high (CVSS 7.7). 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 fo

How urgent is CVE-2026-43820?

Priority 32/100. High severity; Public exploit reference

Software pages

Swift vulnerabilities

References

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