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CVE-2020-20949

22
FAUCET Score

CVE-2020-20949 describes a Bleichenbacher's oracle attack vulnerability affecting the STM32 cryptographic firmware library (UM1924) used in STM32Cube. This flaw allows an unauthenticated attacker to decrypt RSA-encrypted ciphertext by repeatedly querying a server utilizing the vulnerable library, leading to remote information disclosure. Rated Medium severity (CVSS 5.9), the attack has high complexity but can result in a complete compromise of confidentiality. There is currently no evidence of active exploitation, public exploit code (Metasploit, Nuclei, ExploitDB), or significant community discussion surrounding this vulnerability.

Impacted Technologies

VendorProductVersion(s)CPE
Range not provided by sourceCPE matchmatch criteria
cpe:2.3:a:st:stm32cubef0:-:*:*:*:*:*:*:*
Range not provided by sourceCPE matchmatch criteria
cpe:2.3:a:st:stm32cubef1:-:*:*:*:*:*:*:*
Range not provided by sourceCPE matchmatch criteria
cpe:2.3:a:st:stm32cubef2:-:*:*:*:*:*:*:*
Range not provided by sourceCPE matchmatch criteria
cpe:2.3:a:st:stm32cubef3:-:*:*:*:*:*:*:*
Range not provided by sourceCPE matchmatch criteria
cpe:2.3:a:st:stm32cubef4:-:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

5.9MEDIUM

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
NONE
Availability Impact
NONE
Exploitability Score
2.2
Impact Score
3.6
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.92%
Probability of exploitation in next 30 days
EPSS Percentile
56.6%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0092 is in the 14th percentile among its peer group of 19,955 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.0 Bluesky, 0.0 Mastodon, and 0.2 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.0 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Remediation records are not available for this CVE.

References

archiv.infsec.ethz.ch / education/fs08/secsem/bleichenbacher98.pdf
Technical DescriptionThird Party Advisory
bi-zone.medium.com / silence-will-fall-or-how-it-can-take-2-years-to-get-your-vuln-registered-e6134846f5bb
Technical DescriptionThird Party Advisory
st.com / en/embedded-software/x-cube-cryptolib.html
Third Party Advisory