All vulnerabilities
CVE-2026-110310GHSA-322w-f6rw-r4fj

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

Amazon Amazon.Extensions.S3.Encryption
Open in ThreatlineRecord JSON
CVSS
5.3Medium
ExploitationNo known exploitationNot in CISA KEV, which does not prove it is unexploitedCISA KEV
Exploit odds (EPSS)0.51%Chance of exploitation activity in the next 30 days, higher than 42% of CVEs. Scored 23 Oct 2026FIRST EPSS
Fixed inNone listedNo source names a fixed version. Check the vendor advisory below
Published14 Oct 2026Updated 14 Oct 2026CVE List

What fixes it

No source in this snapshot names a fixed version. The vendor advisories under References are the place to check.

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.

Text from CVE List

Affected versions 3

  • Amazon.Extensions.S3.Encryptionaffected: 2.1.0 through 2.*CVE List
  • Amazon.Extensions.S3.Encryptionaffected: 3.0.0 through 3.2.1CVE List
  • Amazon.Extensions.S3.Encryptionaffected: 4.0.0 through 4.0.2CVE List

References 4