RSA PKCS#1 v1.5 padding oracle via legacy envelope key format downgrade in Amazon S3 Encryption Client for .NET
Summary
| CVE | CVE-2026-110310 |
|---|---|
| State | PUBLISHED |
| Assigner | AMZN |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-10-14 20:17:30 UTC |
| Updated | 2026-10-16 15:20:39 UTC |
| 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. |
Risk And Classification
Primary CVSS: v4.0 6 MEDIUM from ff89ba41-3aa1-4d27-914a-91399e9639e5
CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Problem Types: CWE-204 | CWE-757 | CWE-204 CWE-204 Observable response discrepancy | CWE-757 CWE-757 Selection of Less-Secure algorithm during negotiation ('algorithm downgrade')
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 4.0 | ff89ba41-3aa1-4d27-914a-91399e9639e5 | Secondary | 6 | MEDIUM | CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/C... |
| 4.0 | CNA | CVSS | 6 | MEDIUM | CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N |
| 3.1 | ff89ba41-3aa1-4d27-914a-91399e9639e5 | Secondary | 5.3 | MEDIUM | CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N |
| 3.1 | CNA | CVSS | 5.3 | MEDIUM | CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N |
CVSS v4.0 Breakdown
Attack Vector
NetworkAttack Complexity
LowAttack Requirements
PresentPrivileges Required
LowUser Interaction
NoneConfidentiality
HighIntegrity
NoneAvailability
NoneSub Conf.
NoneSub Integrity
NoneSub Availability
NoneCVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CVSS v3.1 Breakdown
Attack Vector
NetworkAttack Complexity
HighPrivileges Required
LowUser Interaction
NoneScope
UnchangedConfidentiality
HighIntegrity
NoneAvailability
NoneCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Amazon | Amazon.Extensions.S3.Encryption | affected 2.1.0 2.* custom | Not specified |
| CNA | Amazon | Amazon.Extensions.S3.Encryption | affected 3.0.0 3.2.1 custom | Not specified |
| CNA | Amazon | Amazon.Extensions.S3.Encryption | affected 4.0.0 4.0.2 custom | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| github.com/aws/amazon-s3-encryption-client-dotnet/security/advisories/GH... | ff89ba41-3aa1-4d27-914a-91399e9639e5 | github.com | |
| aws.amazon.com/security/security-bulletins/2026-135-aws | ff89ba41-3aa1-4d27-914a-91399e9639e5 | aws.amazon.com | |
| www.nuget.org/packages/Amazon.Extensions.S3.Encryption/3.2.2 | ff89ba41-3aa1-4d27-914a-91399e9639e5 | www.nuget.org | |
| www.nuget.org/packages/Amazon.Extensions.S3.Encryption/4.0.3 | ff89ba41-3aa1-4d27-914a-91399e9639e5 | www.nuget.org | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
No vendor comments have been submitted for this CVE.
There are currently no legacy QID mappings associated with this CVE.