CVE-2020-20949Public exploitNetwork attack vector

Ciphertext decryption via PKCS#1 padding oracle

Published Jan 20, 2021 · Updated Jul 9, 2026

Padding-oracle exposure in STMicroelectronics X-CUBE-CRYPTOLIB 3.1.0 and 3.1.2 allows remote attackers to decrypt RSA ciphertexts. The published PoC wraps the RSA PKCS#1 v1.5 decryption routine in a service whose responses distinguish padding success from later parsing failure. Exploitation requires a reachable application that preserves this distinction; ST states that library decryption is constant-time and returns no padding-specific error, making exposure dependent on higher-level behavior.

CVSS severity5.9
Medium
EPSS probability0.93%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Padding-oracle exposure in STMicroelectronics X-CUBE-CRYPTOLIB 3.1.0 and 3.1.2 allows remote attackers to decrypt RSA ciphertexts. The published PoC wraps the RSA PKCS#1 v1.5 decryption routine in a service whose responses distinguish padding success from later parsing failure. Exploitation requires a reachable application that preserves this distinction; ST states that library decryption is constant-time and returns no padding-specific error, making exposure dependent on higher-level behavior.

The record

CVE
CVE-2020-20949
Published
Jan 20, 2021
Updated
Jul 9, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-327
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 20, 2021CVE publishedPublication date reported by the CVE source.
  2. Jul 9, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

4.3NIST NVDAV:N/AC:M/Au:N/C:P/I:N/A:N
5.9NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-327Use of a Broken or Risky Cryptographic Algorithm

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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