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Fencer Vulns
medium 5.3

CVE-2026-110310 json

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

published 2026-10-14 25 d ago modified 2026-10-16 23 d ago also EUVD-2026-101618

cvss
5.3
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 43%
public exploits
0
none known

Summary

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.

Patch / fix

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-110310 updated cvss 5.3

Amazon.Extensions.S3.Encryption: Amazon.Extensions.S3.Encryption: Information disclosure via cryptographic padding downgrade

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
25 d ago

Exploit prediction

0.51% chance of exploitation in the next 30 days, higher than 43% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 5.3 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
CNA 4.0 6.0 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
CNA 4.0 6.0 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

Affected products

  • Amazon Amazon.Extensions.S3.Encryption

Classification

Weakness
  • CWE-204 Observable Response Discrepancy
  • CWE-757 Selection of Less-Secure Algorithm During Negotiation

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.