NIOSSLCertificate._subjectAlternativeNames provides access to the raw bytes for a cert's SANs.

published 2026-07-23 3 mo ago modified 2026-10-24 15 d ago also EUVD-2026-48287

cvss: 7.7; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.1%; EPSS 0.1% chance of exploitation in 30 days, percentile 1%
public exploits: 0; none known

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.

Patch / fix

fixed in 1

Apple swift-nio-ssl 2.37.2

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-43820 updated 2026-08-21 cvss 8.2

swift-nio-ssl: swift-nio-ssl: Out-of-bounds memory access due to improper handling of Subject Alternative Names

Red Hat Hardened Images swift-lang 6.3.3-0.1.hum1
not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation: Proof of concept is public
Automatable: no
Technical impact: partial
Assessed: 3 mo ago (2026-07-24)

Exploit prediction

0.11% chance of exploitation in the next 30 days, higher than 1% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

github.com https://github.com/apple/swift-nio-ssl/security/advisories/GHSA-xfxg-9975-pc2j referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
CISA ADP	3.1	7.7	CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
CNA	3.1	7.7	CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H

Affected products

Apple swift-nio-ssl

Classification

Weakness

CWE-125 Out-of-bounds Read

References

github.com /apple/swift-nio-ssl/security/advisories/GHSA-xfxg-9975-pc2j
exploit, vendor-advisory

Sources

CVE List CVE-2026-43820
NVD CVE-2026-43820

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary