Live › vulnerability › GHSA-322w-f6rw-r4fj
Go to dashboardThe Amazon S3 Encryption Client for .NET can be tricked into switching an object's RSA key wrapping to legacy PKCS#1 v1.5 padding, which is open to Bleichenbacher padding-oracle attacks. A remote user who can read encrypted objects in the bucket could recover the envelope key and decrypt the object.
Summary written from the sources below. Check the originals before acting.
First seen by InfraStack 2026-10-24 20:05 UTC. All times on this page are UTC.
Applications using the Amazon S3 Encryption Client for .NET with the affected version ranges that read client-side encrypted objects from S3 buckets. The attacker needs the ability to read or modify the object's metadata, which the sources describe as a remote user who can read encrypted objects in the bucket. Teams not using this client library, or already on the fixed versions, are not affected.
No product ranges from the sources yet.
AWSSDK.S3Encryption or Amazon S3 Encryption Client package version in the project's .csproj or packages.lock.json, and look for versions >= 2.1.0, 3.0.0 to 3.2.1, or 4.0.0 to 4.0.2.dotnet list package in each .NET solution to list the resolved version.3.2.2 or later.4.0.3 or later.3.2.2 or 4.0.3, since those lines will not be patched.Each row is the first time that source carried this signal. The analyst’s rows are its own findings.
CVE-2026-110310 - RSA PKCS#1 v1.5 padding oracle via legacy envelope key format downgrade in Amazon S3 Encryption Client for .NET
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
Resolution:
This issue has been addressed in Amazon S3 Encryption Client for .NET version 3.2.2 for customers on version 3.x and version 4.0.3 for customers on version 4.x. We recommend upgrading to the latest version and ensuring any forked or derivative code is patched to incorporate the new fixes. The 1.x and 2.x lines will not receive patches; users of those versions need to migrate to version 3.2.2 or 4.0.3.
Workarounds:
None.
References:
Please email [email protected] with any security questions or concerns.
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