---
id: CVE-2026-110310
title: >-
  A remote user who can read encrypted objects in the S3 bucket can force a
  padding downgrade by altering the padding scheme recorded in an object's
  metadata to legacy PKCS#1 v1.5
summary: >-
  A remote user who can read encrypted objects in the S3 bucket can force a
  padding downgrade by altering the padding scheme recorded in an object's
  metadata to legacy PKCS#1 v1.5. Since this padding scheme is susceptible to
  the well-known…
severity: medium
cvss: 5.3
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N'
cwe:
  - CWE-204
  - CWE-757
published: '2026-10-14'
updated: '2026-10-14'
sourceUpdated: '2026-10-14T20:17:30.547'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-110310'
references:
  - url: 'https://aws.amazon.com/security/security-bulletins/2026-135-aws/'
    label: ff89ba41-3aa1-4d27-914a-91399e9639e5
  - url: >-
      https://github.com/aws/amazon-s3-encryption-client-dotnet/security/advisories/GHSA-322w-f6rw-r4fj
    label: ff89ba41-3aa1-4d27-914a-91399e9639e5
  - url: 'https://www.nuget.org/packages/Amazon.Extensions.S3.Encryption/3.2.2'
    label: ff89ba41-3aa1-4d27-914a-91399e9639e5
  - url: 'https://www.nuget.org/packages/Amazon.Extensions.S3.Encryption/4.0.3'
    label: ff89ba41-3aa1-4d27-914a-91399e9639e5
tags:
  - nvd
  - cve.org
ingestedAt: '2026-10-14T20:53:12.375Z'
vendor: Amazon
product: Amazon.Extensions.S3.Encryption
affected:
  - Amazon.Extensions.S3.Encryption >= 2.1.0 <= 2.*
  - Amazon.Extensions.S3.Encryption >= 3.0.0 <= 3.2.1
  - Amazon.Extensions.S3.Encryption >= 4.0.0 <= 4.0.2
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-10-14T19:46:05.003309Z'
---

## Overview

A remote user who can read encrypted objects in the S3 bucket can force a padding downgrade by altering the padding scheme recorded in an object's metadata to legacy PKCS#1 v1.5. Since this padding scheme is susceptible to the well-known Bleichenbacher attack, the user can use a PKCS#1 v1.5 padding oracle to recover the RSA-wrapped envelope key and decrypt the object.



To remediate this issue, we recommend that users upgrade to version 3.2.2 or 4.0.3. The 1.x and 2.x lines will not be patched, users of those lines need to migrate to 3.2.2 or 4.0.3.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.