# CVE-2026-28386: Out-of-bounds Read in AES-CFB-128 on X86-64 with AVX-512 Support

> An out-of-bounds read in OpenSSL's AES-CFB128 implementation on AVX-512 systems can cause a denial of service when processing partial blocks at page boundaries.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/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:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 7 Apr 2026
- **Updated:** 10 Apr 2026
- **Also known as:** DEBIAN-CVE-2026-28386, GHSA-q457-vx59-3fqg

## What is CVE-2026-28386?

CVE-2026-28386 is a critical memory corruption vulnerability in Openssl Openssl, published on 7 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Issue summary: Applications using AES-CFB128 encryption or decryption on
systems with AVX-512 and VAES support can trigger an out-of-bounds read
of up to 15 bytes when processing partial cipher blocks.

Impact summary: This out-of-bounds read may trigger a crash which leads to
Denial of Service for an application if the input buffer ends at a memory
page boundary and the following page is unmapped. There is no information
disclosure as the over-read bytes are not written to output.

The vulnerable code path is only reached when processing partial blocks
(when a previous call left an incomplete block and the current call provides
fewer bytes than needed to complete it). Additionally, the input buffer
must be positioned at a page boundary with the following page unmapped.
CFB mode is not used in TLS/DTLS protocols, which use CBC, GCM, CCM, or
ChaCha20-Poly1305 instead. For these reasons the issue was assessed as
Low severity according to our Security Policy.

Only x86-64 systems with AVX-512 and VAES instruction support are affected.
Other architectures and systems without VAES support use different code
paths that are not affected.

OpenSSL FIPS module in 3.6 version is affected by this issue.

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

## Which versions are affected by CVE-2026-28386?

It affects 1 product.


Products: Openssl Openssl.

## How do I fix CVE-2026-28386?

Apply the vendor's patch.

## Is CVE-2026-28386 being exploited?

There is no known exploitation of CVE-2026-28386 in the wild and no public exploit code.

## Other vulnerabilities in Openssl Openssl

- [CVE-2009-3245](https://insights.sbomify.com/CVE-2009-3245/): Null dereference in n/a (critical 10.0)
- [CVE-2006-3738](https://insights.sbomify.com/CVE-2006-3738/): Memory corruption in n/a (critical 10.0)
- [CVE-2026-63073](https://insights.sbomify.com/CVE-2026-63073/): Untrusted Sender DN Used as Format String in CMP Response Validation (critical 9.8)
- [CVE-2016-6309](https://insights.sbomify.com/CVE-2016-6309/): Use after free in n/a (critical 9.8)
- [CVE-2016-0799](https://insights.sbomify.com/CVE-2016-0799/): Integer overflow in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-28386 and fix it if it is affected.

What it is: CVE-2026-28386 is a critical memory corruption vulnerability in Openssl Openssl, published on 7 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-28386 in the wild and no public exploit code.

Affected product: Openssl Openssl. 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-2026-28386/ (Markdown: https://insights.sbomify.com/CVE-2026-28386/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-28386
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-28386
- OSV: https://osv.dev/vulnerability/CVE-2026-28386

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-28386/
Summaries are generated and may contain mistakes; the official description above is the record.