AWS Security Bulletins: CVE-2026-110310 - RSA PKCS#1 v1.5 padding oracle via legacy envelope key format downgrade in Amazon S3 Encryption Cl
AWS Security Bulletins has published a new security advisory. Here is a summary and what to do.
Key points
- New advisory from AWS Security Bulletins.
- Review affected versions in the advisory.
- Apply updates promptly.
AWS Security Bulletins published a security advisory titled “CVE-2026-110310 - RSA PKCS#1 v1.5 padding oracle via legacy envelope key format downgrade in Amazon S3 Encryption Client for .NET”.
At a glance
- Publisher
- AWS Security Bulletins
- CVEs
- CVE-2026-110310
What the advisory says
Bulletin ID: 2026-135-AWS Scope: AWS Content Type: Important (requires attention) Publication Date: 10/14/2026 12:30 PM PDT Description: We identified CVE-2026-110310, an issue in Amazon S3 encryption client for .NET that could allow 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 Bleichenbacher attack, the user can use a PKCS#1 v1.5 padding oracle to recover the RSA-wrapped envelope key and decrypt the object. Impacted versions: >= 2.1.0; 3.0.0 to 3.2.1; 4.0.0 to 4.0.2 Please refer to the article below for the most up-to-date and complete information related to this AWS Security Bulletin.
What should you do?
- Read the full vendor advisory linked below and confirm whether you run affected versions.
- Schedule the recommended update, prioritising internet-facing systems.
- Watch for exploitation reports; unpatched edge devices are frequent targets.
What to do and how to stay safe: CVE-2026-110310
- Vulnerability severity scores ignore your specific architecture and context.
- Exploitability depends on network exposure and user behavior, not just code flaws.
- Prioritization requires continuous asset inventory and threat intelligence alignment.
Risk-based vulnerability management focuses your limited resources on the flaws that actually threaten your business. Start by mapping your critical assets and checking for active exploits to prioritize your backlog.
Step-by-step guide: Risk-Based Vulnerability Management: Prioritize Fixes by Actual Danger
General security guidance from the Threat Times newsroom. It is not confirmed advice from the organisations named in this story.
