---
id: CVE-2026-28386
title: |-
  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…
summary: |-
  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…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-125
vendor: openssl
product: openssl
affected:
  - 'openssl >= 3.6.0, < 3.6.2'
patched:
  - openssl 3.6.2
published: '2026-04-07'
updated: '2026-07-24'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-28386'
references:
  - url: >-
      https://github.com/openssl/openssl/commit/61f428a2fc6671ede184a19f71e6e495f0689621
    label: openssl-security@openssl.org
  - url: 'https://openssl-library.org/news/secadv/20260407.txt'
    label: openssl-security@openssl.org
tags:
  - nvd
epss: 0.00326
epssPercentile: 0.22958
ingestedAt: '2026-07-25T23:05:58.078Z'
---

## Overview

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.

## Affected

- `openssl >= 3.6.0, < 3.6.2`

## Remediation

Upgrade past the affected range:

- `openssl 3.6.2`