# CVE-2026-43820: Memory corruption in swift-nio-ssl

> Out-of-bounds memory access in swift-nio-ssl allows attackers to potentially execute code or cause denial of service via crafted SSL certificates.

- **Severity:** High 7.7 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 23 Jul 2026
- **Updated:** 24 Jul 2026
- **Also known as:** GHSA-xfxg-9975-pc2j

## What is CVE-2026-43820?

CVE-2026-43820 is a high-severity memory corruption vulnerability in Apple swift-nio-ssl, published on 23 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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.

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-43820?

It affects 1 product.


Products: Apple Swiftnio Ssl.

## How do I fix CVE-2026-43820?

No fix has been published for CVE-2026-43820 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-43820 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-43820 exists.

## Other vulnerabilities in Apple swift-nio-ssl

- [CVE-2019-8849](https://insights.sbomify.com/CVE-2019-8849/): SwiftNIO SSL arbitrary code execution vulnerability (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-43820 and fix it if it is affected.

What it is: CVE-2026-43820 is a high-severity memory corruption vulnerability in Apple swift-nio-ssl, published on 23 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-43820 exists.

Affected product: Apple swift-nio-ssl. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-43820/ (Markdown: https://insights.sbomify.com/CVE-2026-43820/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-43820
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-43820
- OSV: https://osv.dev/vulnerability/CVE-2026-43820

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-43820/
Summaries are generated and may contain mistakes; the official description above is the record.