# CVE-2026-110310: RSA PKCS#1 v1.5 padding oracle via legacy envelope key format downgrade in Amazon S3 Encryption Client for .NET

> CVE-2026-110310: RSA PKCS#1 v1.5 padding oracle via legacy envelope key format downgrade in Amazon S3 Encryption Client for .NET. CVSS 5.3 (CVSS 3.1).

Canonical: https://rewindex.com/cve/CVE-2026-110310
Last updated: 2026-10-16T15:20:39Z

- Published: 2026-10-14 19:37 UTC · Updated: 2026-10-16 15:20 UTC · Assigner: AMZN
- CVSS: 5.3 (CVSS 3.1) · Severity: Medium · Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
- EPSS: 0.51%, 43th percentile (scored 2026-10-25)
- CISA KEV: no
- CWE: CWE-204, CWE-757

## Description

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.

## Affected vendors and products

- Amazon: Amazon.Extensions.S3.Encryption

## Tracked companies

- [Amazon Web Services](https://rewindex.com/company/aws.md)

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2026-110310)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-110310)
- [https://aws.amazon.com/security/security-bulletins/2026-135-aws/](https://aws.amazon.com/security/security-bulletins/2026-135-aws/)
- [https://github.com/aws/amazon-s3-encryption-client-dotnet/security/advisories/GHSA-322w-f6rw-r4fj](https://github.com/aws/amazon-s3-encryption-client-dotnet/security/advisories/GHSA-322w-f6rw-r4fj)
- [https://www.nuget.org/packages/Amazon.Extensions.S3.Encryption/3.2.2](https://www.nuget.org/packages/Amazon.Extensions.S3.Encryption/3.2.2)
- [https://www.nuget.org/packages/Amazon.Extensions.S3.Encryption/4.0.3](https://www.nuget.org/packages/Amazon.Extensions.S3.Encryption/4.0.3)

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_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


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Canonical: https://rewindex.com/cve/CVE-2026-110310 · Markdown: https://rewindex.com/cve/CVE-2026-110310.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-110310 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T03:12:05.109Z