CVE-2020-20949

Bleichenbacher's attack on PKCS #1 v1.5 padding for RSA in STM32 cryptographic firmware library software expansion for STM32Cube (UM1924). The vulnerability can allow one to use Bleichenbacher's oracle attack to decrypt an encrypted ciphertext by making successive queries to the server using the vulnerable library, resulting in remote information disclosure.

Published: 2021-01-20 Last update: 2026-07-05 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2020-20949 is rated Moderate Risk (43.3/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 0.92%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2020-20949

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.59% 0.92% +0.33%
2 2026-04-16 0.54% 0.59% +0.05%
3 2025-11-05 — 0.54% —

Full EPSS history (12 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2020-20949

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.9 3.1 MEDIUM
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 2.2 3.6 [email protected]
4.3 2.0 MEDIUM
AV:N/AC:M/Au:N/C:P/I:N/A:N Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:N)
No availability impact.
 8.6 2.9 [email protected]

Weakness enumeration for CVE-2020-20949

GitHub Security Advisory for CVE-2020-20949

GHSA-7p98-xcgc-gwhj · Severity: medium — Bleichenbacher's attack on PKCS #1 v1.5 padding for RSA in STM32 cryptographic firmware library...

Affected software / configurations for CVE-2020-20949

Vendor Product Version Raw CPE
st stm32cubef0 — cpe:2.3:a:st:stm32cubef0:-:*:*:*:*:*:*:*
st stm32cubef1 — cpe:2.3:a:st:stm32cubef1:-:*:*:*:*:*:*:*
st stm32cubef2 — cpe:2.3:a:st:stm32cubef2:-:*:*:*:*:*:*:*
st stm32cubef3 — cpe:2.3:a:st:stm32cubef3:-:*:*:*:*:*:*:*
st stm32cubef4 — cpe:2.3:a:st:stm32cubef4:-:*:*:*:*:*:*:*
st stm32cubef7 — cpe:2.3:a:st:stm32cubef7:-:*:*:*:*:*:*:*
st stm32cubeg0 — cpe:2.3:a:st:stm32cubeg0:-:*:*:*:*:*:*:*
st stm32cubeg4 — cpe:2.3:a:st:stm32cubeg4:-:*:*:*:*:*:*:*
st stm32cubeh7 — cpe:2.3:a:st:stm32cubeh7:-:*:*:*:*:*:*:*
st stm32cubeide — cpe:2.3:a:st:stm32cubeide:-:*:*:*:*:*:*:*
st stm32cubel0 — cpe:2.3:a:st:stm32cubel0:-:*:*:*:*:*:*:*
st stm32cubel1 — cpe:2.3:a:st:stm32cubel1:-:*:*:*:*:*:*:*
st stm32cubel4 — cpe:2.3:a:st:stm32cubel4:-:*:*:*:*:*:*:*
st stm32cubel4\+ — cpe:2.3:a:st:stm32cubel4\+:-:*:*:*:*:*:*:*
st stm32cubel5 — cpe:2.3:a:st:stm32cubel5:-:*:*:*:*:*:*:*
st stm32cubemonitor — cpe:2.3:a:st:stm32cubemonitor:-:*:*:*:*:*:*:*
st stm32cubemp1 — cpe:2.3:a:st:stm32cubemp1:-:*:*:*:*:*:*:*
st stm32cubemx — cpe:2.3:a:st:stm32cubemx:-:*:*:*:*:*:*:*
st stm32cubeprogrammer — cpe:2.3:a:st:stm32cubeprogrammer:-:*:*:*:*:*:*:*
st stm32cubewb — cpe:2.3:a:st:stm32cubewb:-:*:*:*:*:*:*:*
st stm32cubewl — cpe:2.3:a:st:stm32cubewl:-:*:*:*:*:*:*:*
ietf public_key_cryptography_standards_\#1 1.5 cpe:2.3:a:ietf:public_key_cryptography_standards_\#1:1.5:*:*:*:*:*:*:*

References for CVE-2020-20949

cvelogic Threat Intelligence