CVE-2026-110310: amazon amazon.extensions.s3.encryption Observable Response Discrepancy

Vulnerability summary

CVE-2026-110310 is a medium (CVSS 6.0) Observable Response Discrepancy vulnerability in amazon amazon.extensions.s3.encryption. EPSS estimates a 0.51% chance of exploitation in the next 30 days, higher than 42.1% of scored vulnerabilities.

Timeline

1. 14-10-2026
   PublishedVulnerability first disclosed.
2. 14-10-2026
   Last modifiedVulnerability information updated.

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.

• CWE-204Observable Response DiscrepancyThe product provides different responses to incoming requests in a way that reveals internal state information to an unauthorized actor outside of the intended control sphere.
• CWE-757Selection of Less-Secure Algorithm During Negotiation ('Algorithm Downgrade')A protocol or its implementation supports interaction between multiple actors and allows those actors to negotiate which algorithm should be used as a protection mechanism such as encryption or authentication, but it does not select the strongest algorithm that is available to both parties.