CVE-2026-110310
RSA PKCS#1 v1.5 padding oracle via legacy envelope key format downgrade in Amazon S3 Encryption Client for .NET
CVSS Score
5.3
EPSS Score
0.0%
EPSS Percentile
0th
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.
| CWE | CWE-204 CWE-757 |
| Vendor | amazon |
| Product | amazon.extensions.s3.encryption |
| Published | Oct 14, 2026 |
| Last Updated | Oct 14, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N Attack Vector
Network
Attack Complexity
High
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None
Affected Versions
Amazon / Amazon.Extensions.S3.Encryption
2.1.0 ≤ 2.* 3.0.0 ≤ 3.2.1 4.0.0 ≤ 4.0.2
References
nuget.org: https://www.nuget.org/packages/Amazon.Extensions.S3.Encryption/3.2.2 nuget.org: https://www.nuget.org/packages/Amazon.Extensions.S3.Encryption/4.0.3 aws.amazon.com: https://aws.amazon.com/security/security-bulletins/2026-135-aws/ github.com: https://github.com/aws/amazon-s3-encryption-client-dotnet/security/advisories/GHSA-322w-f6rw-r4fj